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git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux
Pull btrfs updates from David Sterba:
"New features:
- raid-stripe-tree
New tree for logical file extent mapping where the physical mapping
may not match on multiple devices. This is now used in zoned mode
to implement RAID0/RAID1* profiles, but can be used in non-zoned
mode as well. The support for RAID56 is in development and will
eventually fix the problems with the current implementation. This
is a backward incompatible feature and has to be enabled at mkfs
time.
- simple quota accounting (squota)
A simplified mode of qgroup that accounts all space on the initial
extent owners (a subvolume), the snapshots are then cheap to create
and delete. The deletion of snapshots in fully accounting qgroups
is a known CPU/IO performance bottleneck.
The squota is not suitable for the general use case but works well
for containers where the original subvolume exists for the whole
time. This is a backward incompatible feature as it needs extending
some structures, but can be enabled on an existing filesystem.
- temporary filesystem fsid (temp_fsid)
The fsid identifies a filesystem and is hard coded in the
structures, which disallows mounting the same fsid found on
different devices.
For a single device filesystem this is not strictly necessary, a
new temporary fsid can be generated on mount e.g. after a device is
cloned. This will be used by Steam Deck for root partition A/B
testing, or can be used for VM root images.
Other user visible changes:
- filesystems with partially finished metadata_uuid conversion cannot
be mounted anymore and the uuid fixup has to be done by btrfs-progs
(btrfstune).
Performance improvements:
- reduce reservations for checksum deletions (with enabled free space
tree by factor of 4), on a sample workload on file with many
extents the deletion time decreased by 12%
- make extent state merges more efficient during insertions, reduce
rb-tree iterations (run time of critical functions reduced by 5%)
Core changes:
- the integrity check functionality has been removed, this was a
debugging feature and removal does not affect other integrity
checks like checksums or tree-checker
- space reservation changes:
- more efficient delayed ref reservations, this avoids building up
too much work or overusing or exhausting the global block
reserve in some situations
- move delayed refs reservation to the transaction start time,
this prevents some ENOSPC corner cases related to exhaustion of
global reserve
- improvements in reducing excessive reservations for block group
items
- adjust overcommit logic in near full situations, account for one
more chunk to eventually allocate metadata chunk, this is mostly
relevant for small filesystems (<10GiB)
- single device filesystems are scanned but not registered (except
seed devices), this allows temp_fsid to work
- qgroup iterations do not need GFP_ATOMIC allocations anymore
- cleanups, refactoring, reduced data structure size, function
parameter simplifications, error handling fixes"
* tag 'for-6.7-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux: (156 commits)
btrfs: open code timespec64 in struct btrfs_inode
btrfs: remove redundant log root tree index assignment during log sync
btrfs: remove redundant initialization of variable dirty in btrfs_update_time()
btrfs: sysfs: show temp_fsid feature
btrfs: disable the device add feature for temp-fsid
btrfs: disable the seed feature for temp-fsid
btrfs: update comment for temp-fsid, fsid, and metadata_uuid
btrfs: remove pointless empty log context list check when syncing log
btrfs: update comment for struct btrfs_inode::lock
btrfs: remove pointless barrier from btrfs_sync_file()
btrfs: add and use helpers for reading and writing last_trans_committed
btrfs: add and use helpers for reading and writing fs_info->generation
btrfs: add and use helpers for reading and writing log_transid
btrfs: add and use helpers for reading and writing last_log_commit
btrfs: support cloned-device mount capability
btrfs: add helper function find_fsid_by_disk
btrfs: stop reserving excessive space for block group item insertions
btrfs: stop reserving excessive space for block group item updates
btrfs: reorder btrfs_inode to fill gaps
btrfs: open code btrfs_ordered_inode_tree in btrfs_inode
...
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When creating a snapshot of a subvolume that was created in the current
transaction, we can end up not persisting a dirty extent buffer that is
referenced by the snapshot, resulting in IO errors due to checksum failures
when trying to read the extent buffer later from disk. A sequence of steps
that leads to this is the following:
1) At ioctl.c:create_subvol() we allocate an extent buffer, with logical
address 36007936, for the leaf/root of a new subvolume that has an ID
of 291. We mark the extent buffer as dirty, and at this point the
subvolume tree has a single node/leaf which is also its root (level 0);
2) We no longer commit the transaction used to create the subvolume at
create_subvol(). We used to, but that was recently removed in
commit 1b53e51a4a8f ("btrfs: don't commit transaction for every subvol
create");
3) The transaction used to create the subvolume has an ID of 33, so the
extent buffer 36007936 has a generation of 33;
4) Several updates happen to subvolume 291 during transaction 33, several
files created and its tree height changes from 0 to 1, so we end up with
a new root at level 1 and the extent buffer 36007936 is now a leaf of
that new root node, which is extent buffer 36048896.
The commit root remains as 36007936, since we are still at transaction
33;
5) Creation of a snapshot of subvolume 291, with an ID of 292, starts at
ioctl.c:create_snapshot(). This triggers a commit of transaction 33 and
we end up at transaction.c:create_pending_snapshot(), in the critical
section of a transaction commit.
There we COW the root of subvolume 291, which is extent buffer 36048896.
The COW operation returns extent buffer 36048896, since there's no need
to COW because the extent buffer was created in this transaction and it
was not written yet.
The we call btrfs_copy_root() against the root node 36048896. During
this operation we allocate a new extent buffer to turn into the root
node of the snapshot, copy the contents of the root node 36048896 into
this snapshot root extent buffer, set the owner to 292 (the ID of the
snapshot), etc, and then we call btrfs_inc_ref(). This will create a
delayed reference for each leaf pointed by the root node with a
reference root of 292 - this includes a reference for the leaf
36007936.
After that we set the bit BTRFS_ROOT_FORCE_COW in the root's state.
Then we call btrfs_insert_dir_item(), to create the directory entry in
in the tree of subvolume 291 that points to the snapshot. This ends up
needing to modify leaf 36007936 to insert the respective directory
items. Because the bit BTRFS_ROOT_FORCE_COW is set for the root's state,
we need to COW the leaf. We end up at btrfs_force_cow_block() and then
at update_ref_for_cow().
At update_ref_for_cow() we call btrfs_block_can_be_shared() which
returns false, despite the fact the leaf 36007936 is shared - the
subvolume's root and the snapshot's root point to that leaf. The
reason that it incorrectly returns false is because the commit root
of the subvolume is extent buffer 36007936 - it was the initial root
of the subvolume when we created it. So btrfs_block_can_be_shared()
which has the following logic:
int btrfs_block_can_be_shared(struct btrfs_root *root,
struct extent_buffer *buf)
{
if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state) &&
buf != root->node && buf != root->commit_root &&
(btrfs_header_generation(buf) <=
btrfs_root_last_snapshot(&root->root_item) ||
btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)))
return 1;
return 0;
}
Returns false (0) since 'buf' (extent buffer 36007936) matches the
root's commit root.
As a result, at update_ref_for_cow(), we don't check for the number
of references for extent buffer 36007936, we just assume it's not
shared and therefore that it has only 1 reference, so we set the local
variable 'refs' to 1.
Later on, in the final if-else statement at update_ref_for_cow():
static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct extent_buffer *buf,
struct extent_buffer *cow,
int *last_ref)
{
(...)
if (refs > 1) {
(...)
} else {
(...)
btrfs_clear_buffer_dirty(trans, buf);
*last_ref = 1;
}
}
So we mark the extent buffer 36007936 as not dirty, and as a result
we don't write it to disk later in the transaction commit, despite the
fact that the snapshot's root points to it.
Attempting to access the leaf or dumping the tree for example shows
that the extent buffer was not written:
$ btrfs inspect-internal dump-tree -t 292 /dev/sdb
btrfs-progs v6.2.2
file tree key (292 ROOT_ITEM 33)
node 36110336 level 1 items 2 free space 119 generation 33 owner 292
node 36110336 flags 0x1(WRITTEN) backref revision 1
checksum stored a8103e3e
checksum calced a8103e3e
fs uuid 90c9a46f-ae9f-4626-9aff-0cbf3e2e3a79
chunk uuid e8c9c885-78f4-4d31-85fe-89e5f5fd4a07
key (256 INODE_ITEM 0) block 36007936 gen 33
key (257 EXTENT_DATA 0) block 36052992 gen 33
checksum verify failed on 36007936 wanted 0x00000000 found 0x86005f29
checksum verify failed on 36007936 wanted 0x00000000 found 0x86005f29
total bytes 107374182400
bytes used 38572032
uuid 90c9a46f-ae9f-4626-9aff-0cbf3e2e3a79
The respective on disk region is full of zeroes as the device was
trimmed at mkfs time.
Obviously 'btrfs check' also detects and complains about this:
$ btrfs check /dev/sdb
Opening filesystem to check...
Checking filesystem on /dev/sdb
UUID: 90c9a46f-ae9f-4626-9aff-0cbf3e2e3a79
generation: 33 (33)
[1/7] checking root items
[2/7] checking extents
checksum verify failed on 36007936 wanted 0x00000000 found 0x86005f29
checksum verify failed on 36007936 wanted 0x00000000 found 0x86005f29
checksum verify failed on 36007936 wanted 0x00000000 found 0x86005f29
bad tree block 36007936, bytenr mismatch, want=36007936, have=0
owner ref check failed [36007936 4096]
ERROR: errors found in extent allocation tree or chunk allocation
[3/7] checking free space tree
[4/7] checking fs roots
checksum verify failed on 36007936 wanted 0x00000000 found 0x86005f29
checksum verify failed on 36007936 wanted 0x00000000 found 0x86005f29
checksum verify failed on 36007936 wanted 0x00000000 found 0x86005f29
bad tree block 36007936, bytenr mismatch, want=36007936, have=0
The following tree block(s) is corrupted in tree 292:
tree block bytenr: 36110336, level: 1, node key: (256, 1, 0)
root 292 root dir 256 not found
ERROR: errors found in fs roots
found 38572032 bytes used, error(s) found
total csum bytes: 16048
total tree bytes: 1265664
total fs tree bytes: 1118208
total extent tree bytes: 65536
btree space waste bytes: 562598
file data blocks allocated: 65978368
referenced 36569088
Fix this by updating btrfs_block_can_be_shared() to consider that an
extent buffer may be shared if it matches the commit root and if its
generation matches the current transaction's generation.
This can be reproduced with the following script:
$ cat test.sh
#!/bin/bash
MNT=/mnt/sdi
DEV=/dev/sdi
# Use a filesystem with a 64K node size so that we have the same node
# size on every machine regardless of its page size (on x86_64 default
# node size is 16K due to the 4K page size, while on PPC it's 64K by
# default). This way we can make sure we are able to create a btree for
# the subvolume with a height of 2.
mkfs.btrfs -f -n 64K $DEV
mount $DEV $MNT
btrfs subvolume create $MNT/subvol
# Create a few empty files on the subvolume, this bumps its btree
# height to 2 (root node at level 1 and 2 leaves).
for ((i = 1; i <= 300; i++)); do
echo -n > $MNT/subvol/file_$i
done
btrfs subvolume snapshot -r $MNT/subvol $MNT/subvol/snap
umount $DEV
btrfs check $DEV
Running it on a 6.5 kernel (or any 6.6-rc kernel at the moment):
$ ./test.sh
Create subvolume '/mnt/sdi/subvol'
Create a readonly snapshot of '/mnt/sdi/subvol' in '/mnt/sdi/subvol/snap'
Opening filesystem to check...
Checking filesystem on /dev/sdi
UUID: bbdde2ff-7d02-45ca-8a73-3c36f23755a1
[1/7] checking root items
[2/7] checking extents
parent transid verify failed on 30539776 wanted 7 found 5
parent transid verify failed on 30539776 wanted 7 found 5
parent transid verify failed on 30539776 wanted 7 found 5
Ignoring transid failure
owner ref check failed [30539776 65536]
ERROR: errors found in extent allocation tree or chunk allocation
[3/7] checking free space tree
[4/7] checking fs roots
parent transid verify failed on 30539776 wanted 7 found 5
Ignoring transid failure
Wrong key of child node/leaf, wanted: (256, 1, 0), have: (2, 132, 0)
Wrong generation of child node/leaf, wanted: 5, have: 7
root 257 root dir 256 not found
ERROR: errors found in fs roots
found 917504 bytes used, error(s) found
total csum bytes: 0
total tree bytes: 851968
total fs tree bytes: 393216
total extent tree bytes: 65536
btree space waste bytes: 736550
file data blocks allocated: 0
referenced 0
A test case for fstests will follow soon.
Fixes: 1b53e51a4a8f ("btrfs: don't commit transaction for every subvol create")
CC: stable@vger.kernel.org # 6.5+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The btrfs_backref_cache::is_reloc is an indicator variable and should
use a bool type.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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In order to implement simple quota groups, we need to be able to
associate a data extent with the subvolume that created it. Once you
account for reflink, this information cannot be recovered without
explicitly storing it. Options for storing it are:
- a new key/item
- a new extent inline ref item
The former is backwards compatible, but wastes space, the latter is
incompat, but is efficient in space and reuses the existing inline ref
machinery, while only abusing it a tiny amount -- specifically, the new
item is not a ref, per-se.
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
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The v0 extent item has been deprecated for a long time, and we don't have
any report from the community either.
So it's time to remove the v0 extent specific error handling, and just
treat them as regular extent tree corruption.
This patch would remove the btrfs_print_v0_err() helper, and enhance the
involved error handling to treat them just as any extent tree
corruption. No reports regarding v0 extents have been seen since the
graceful handling was added in 2018.
This involves:
- btrfs_backref_add_tree_node()
This change is a little tricky, the new code is changed to only handle
BTRFS_TREE_BLOCK_REF_KEY and BTRFS_SHARED_BLOCK_REF_KEY.
But this is safe, as we have rejected any unknown inline refs through
btrfs_get_extent_inline_ref_type().
For keyed backrefs, we're safe to skip anything we don't know (that's
if it can pass tree-checker in the first place).
- btrfs_lookup_extent_info()
- lookup_inline_extent_backref()
- run_delayed_extent_op()
- __btrfs_free_extent()
- add_tree_block()
Regular error handling of unexpected extent tree item, and abort
transaction (if we have a trans handle).
- remove_extent_data_ref()
It's pretty much the same as the regular rejection of unknown backref
key.
But for this particular case, we can also remove a BUG_ON().
- extent_data_ref_count()
We can remove the BTRFS_EXTENT_REF_V0_KEY BUG_ON(), as it would be
rejected by the only caller.
- btrfs_print_leaf()
Remove the handling for BTRFS_EXTENT_REF_V0_KEY.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When using the logical to ino ioctl v2, if the flag to ignore offsets of
file extent items (BTRFS_LOGICAL_INO_ARGS_IGNORE_OFFSET) is given, the
backref walking code ends up not returning references for all file offsets
of an inode that point to the given logical bytenr. This happens since
kernel 6.2, commit 6ce6ba534418 ("btrfs: use a single argument for extent
offset in backref walking functions") because:
1) It mistakenly skipped the search for file extent items in a leaf that
point to the target extent if that flag is given. Instead it should
only skip the filtering done by check_extent_in_eb() - that is, it
should not avoid the calls to that function (or find_extent_in_eb(),
which uses it).
2) It was also not building a list of inode extent elements (struct
extent_inode_elem) if we have multiple inode references for an extent
when the ignore offset flag is given to the logical to ino ioctl - it
would leave a single element, only the last one that was found.
These stem from the confusing old interface for backref walking functions
where we had an extent item offset argument that was a pointer to a u64
and another boolean argument that indicated if the offset should be
ignored, but the pointer could be NULL. That NULL case is used by
relocation, qgroup extent accounting and fiemap, simply to avoid building
the inode extent list for each reference, as it's not necessary for those
use cases and therefore avoids memory allocations and some computations.
Fix this by adding a boolean argument to the backref walk context
structure to indicate that the inode extent list should not be built,
make relocation set that argument to true and fix the backref walking
logic to skip the calls to check_extent_in_eb() and find_extent_in_eb()
only if this new argument is true, instead of 'ignore_extent_item_pos'
being true.
A test case for fstests will be added soon, to provide cover not only
for these cases but to the logical to ino ioctl in general as well, as
currently we do not have a test case for it.
Reported-by: Vladimir Panteleev <git@vladimir.panteleev.md>
Link: https://lore.kernel.org/linux-btrfs/CAHhfkvwo=nmzrJSqZ2qMfF-rZB-ab6ahHnCD_sq9h4o8v+M7QQ@mail.gmail.com/
Fixes: 6ce6ba534418 ("btrfs: use a single argument for extent offset in backref walking functions")
CC: stable@vger.kernel.org # 6.2+
Tested-by: Vladimir Panteleev <git@vladimir.panteleev.md>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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During fiemap, when walking backreferences to determine if a b+tree
node/leaf is shared, we may find a tree block (leaf or node) for which
two parents were added to the references ulist. This happens if we get
for example one direct ref (shared tree block ref) and one indirect ref
(non-shared tree block ref) for the tree block at the current level,
which can happen during relocation.
In that case the fiemap path cache can not be used since it's meant for
a single path, with one tree block at each possible level, so having
multiple references for a tree block at any level may result in getting
the level counter exceed BTRFS_MAX_LEVEL and eventually trigger the
warning:
WARN_ON_ONCE(level >= BTRFS_MAX_LEVEL)
at lookup_backref_shared_cache() and at store_backref_shared_cache().
This is harmless since the code ignores any level >= BTRFS_MAX_LEVEL, the
warning is there just to catch any unexpected case like the one described
above. However if a user finds this it may be scary and get reported.
So just ignore the path cache once we find a tree block for which there
are more than one reference, which is the less common case, and update
the cache with the sharedness check result for all levels below the level
for which we found multiple references.
Reported-by: Jarno Pelkonen <jarno.pelkonen@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CAKv8qLmDNAGJGCtsevxx_VZ_YOvvs1L83iEJkTgyA4joJertng@mail.gmail.com/
Fixes: 12a824dc67a6 ("btrfs: speedup checking for extent sharedness during fiemap")
CC: stable@vger.kernel.org # 6.1+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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During fiemap, when checking if a data extent is shared we are doing the
backref walking even if we already know the leaf is shared, which is a
waste of time since if the leaf shared then the data extent is also
shared. So skip the backref walking when we know we are in a shared leaf.
The following test was measures the gains for a case where all leaves
are shared due to a snapshot:
$ cat test.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
umount $DEV &> /dev/null
mkfs.btrfs -f $DEV
# Use compression to quickly create files with a lot of extents
# (each with a size of 128K).
mount -o compress=lzo $DEV $MNT
# 40G gives 327680 extents, each with a size of 128K.
xfs_io -f -c "pwrite -S 0xab -b 1M 0 40G" $MNT/foobar
# Add some more files to increase the size of the fs and extent
# trees (in the real world there's a lot of files and extents
# from other files).
xfs_io -f -c "pwrite -S 0xcd -b 1M 0 20G" $MNT/file1
xfs_io -f -c "pwrite -S 0xef -b 1M 0 20G" $MNT/file2
xfs_io -f -c "pwrite -S 0x73 -b 1M 0 20G" $MNT/file3
# Create a snapshot so all the extents become indirectly shared
# through subtrees, with a generation less than or equals to the
# generation used to create the snapshot.
btrfs subvolume snapshot -r $MNT $MNT/snap1
# Unmount and mount again to clear cached metadata.
umount $MNT
mount -o compress=lzo $DEV $MNT
start=$(date +%s%N)
# The filefrag tool uses the fiemap ioctl.
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds (metadata not cached)"
echo
start=$(date +%s%N)
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds (metadata cached)"
umount $MNT
The results were the following on a non-debug kernel (Debian's default
kernel config).
Before this patch:
(...)
/mnt/sdi/foobar: 327680 extents found
fiemap took 1821 milliseconds (metadata not cached)
/mnt/sdi/foobar: 327680 extents found
fiemap took 399 milliseconds (metadata cached)
After this patch:
(...)
/mnt/sdi/foobar: 327680 extents found
fiemap took 591 milliseconds (metadata not cached)
/mnt/sdi/foobar: 327680 extents found
fiemap took 123 milliseconds (metadata cached)
That's a speedup of 3.1x and 3.2x.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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During fiemap, when accessing the cache that stores the sharedness of an
extent, we need to either be holding a transaction handle or the commit
root semaphore. I left comments about this in the comment that precedes
store_backref_shared_cache() and lookup_backref_shared_cache(), but have
actually not enforced it through assertions. So assert that the commit
root semaphore is held if we are not holding a transaction handle.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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If a file consists of an inline extent followed by a regular or prealloc
extent, then a legitimate attempt to resolve a logical address in the
non-inline region will result in add_all_parents reading the invalid
offset field of the inline extent. If the inline extent item is placed
in the leaf eb s.t. it is the first item, attempting to access the
offset field will not only be meaningless, it will go past the end of
the eb and cause this panic:
[17.626048] BTRFS warning (device dm-2): bad eb member end: ptr 0x3fd4 start 30834688 member offset 16377 size 8
[17.631693] general protection fault, probably for non-canonical address 0x5088000000000: 0000 [#1] SMP PTI
[17.635041] CPU: 2 PID: 1267 Comm: btrfs Not tainted 5.12.0-07246-g75175d5adc74-dirty #199
[17.637969] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[17.641995] RIP: 0010:btrfs_get_64+0xe7/0x110
[17.649890] RSP: 0018:ffffc90001f73a08 EFLAGS: 00010202
[17.651652] RAX: 0000000000000001 RBX: ffff88810c42d000 RCX: 0000000000000000
[17.653921] RDX: 0005088000000000 RSI: ffffc90001f73a0f RDI: 0000000000000001
[17.656174] RBP: 0000000000000ff9 R08: 0000000000000007 R09: c0000000fffeffff
[17.658441] R10: ffffc90001f73790 R11: ffffc90001f73788 R12: ffff888106afe918
[17.661070] R13: 0000000000003fd4 R14: 0000000000003f6f R15: cdcdcdcdcdcdcdcd
[17.663617] FS: 00007f64e7627d80(0000) GS:ffff888237c80000(0000) knlGS:0000000000000000
[17.666525] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[17.668664] CR2: 000055d4a39152e8 CR3: 000000010c596002 CR4: 0000000000770ee0
[17.671253] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[17.673634] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[17.676034] PKRU: 55555554
[17.677004] Call Trace:
[17.677877] add_all_parents+0x276/0x480
[17.679325] find_parent_nodes+0xfae/0x1590
[17.680771] btrfs_find_all_leafs+0x5e/0xa0
[17.682217] iterate_extent_inodes+0xce/0x260
[17.683809] ? btrfs_inode_flags_to_xflags+0x50/0x50
[17.685597] ? iterate_inodes_from_logical+0xa1/0xd0
[17.687404] iterate_inodes_from_logical+0xa1/0xd0
[17.689121] ? btrfs_inode_flags_to_xflags+0x50/0x50
[17.691010] btrfs_ioctl_logical_to_ino+0x131/0x190
[17.692946] btrfs_ioctl+0x104a/0x2f60
[17.694384] ? selinux_file_ioctl+0x182/0x220
[17.695995] ? __x64_sys_ioctl+0x84/0xc0
[17.697394] __x64_sys_ioctl+0x84/0xc0
[17.698697] do_syscall_64+0x33/0x40
[17.700017] entry_SYSCALL_64_after_hwframe+0x44/0xae
[17.701753] RIP: 0033:0x7f64e72761b7
[17.709355] RSP: 002b:00007ffefb067f58 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[17.712088] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f64e72761b7
[17.714667] RDX: 00007ffefb067fb0 RSI: 00000000c0389424 RDI: 0000000000000003
[17.717386] RBP: 00007ffefb06d188 R08: 000055d4a390d2b0 R09: 00007f64e7340a60
[17.719938] R10: 0000000000000231 R11: 0000000000000246 R12: 0000000000000001
[17.722383] R13: 0000000000000000 R14: 00000000c0389424 R15: 000055d4a38fd2a0
[17.724839] Modules linked in:
Fix the bug by detecting the inline extent item in add_all_parents and
skipping to the next extent item.
CC: stable@vger.kernel.org # 4.9+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
Move struct btrfs_tree_parent_check out of disk-io.h so that volumes.h
an various .c files don't have to include disk-io.h just for it.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
[ use tree-checker.h for the structure ]
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
There are several different tree block parentness check parameters used
across several helpers:
- level
Mandatory
- transid
Under most cases it's mandatory, but there are several backref cases
which skips this check.
- owner_root
- first_key
Utilized by most top-down tree search routine. Otherwise can be
skipped.
Those four members are not always mandatory checks, and some of them are
the same u64, which means if some arguments got swapped compiler will
not catch it.
Furthermore if we're going to further expand the parentness check, we
need to modify quite some helpers just to add one more parameter.
This patch will concentrate all these members into a structure called
btrfs_tree_parent_check, and pass that structure for the following
helpers:
- btrfs_read_extent_buffer()
- read_tree_block()
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
When doing backref walking to determine a source range to clone from, it
is worthless to collect and resolve our own data backref, as we can't
obviously use it as a clone source and it represents the range we want to
clone into. Collecting the backref implies doing the extra work to resolve
it, doing the search for a file extent item in a subvolume tree, etc.
Skipping the data backref is valid as long as we only have the send root
as the single clone root, otherwise the leaf with the file extent item may
be accessible from another clone root due to shared subtrees created by
snapshots, and therefore we have to collect the backref and resolve it.
So add a callback to the backref walking code to guide it to skip data
backrefs.
This change is part of a patchset comprised of the following patches:
01/17 btrfs: fix inode list leak during backref walking at resolve_indirect_refs()
02/17 btrfs: fix inode list leak during backref walking at find_parent_nodes()
03/17 btrfs: fix ulist leaks in error paths of qgroup self tests
04/17 btrfs: remove pointless and double ulist frees in error paths of qgroup tests
05/17 btrfs: send: avoid unnecessary path allocations when finding extent clone
06/17 btrfs: send: update comment at find_extent_clone()
07/17 btrfs: send: drop unnecessary backref context field initializations
08/17 btrfs: send: avoid unnecessary backref lookups when finding clone source
09/17 btrfs: send: optimize clone detection to increase extent sharing
10/17 btrfs: use a single argument for extent offset in backref walking functions
11/17 btrfs: use a structure to pass arguments to backref walking functions
12/17 btrfs: reuse roots ulist on each leaf iteration for iterate_extent_inodes()
13/17 btrfs: constify ulist parameter of ulist_next()
14/17 btrfs: send: cache leaf to roots mapping during backref walking
15/17 btrfs: send: skip unnecessary backref iterations
16/17 btrfs: send: avoid double extent tree search when finding clone source
17/17 btrfs: send: skip resolution of our own backref when finding clone source
The following test was run on non-debug kernel (Debian's default kernel
config) before and after applying the patchset:
$ cat test-send-many-shared-extents.sh
#!/bin/bash
DEV=/dev/sdh
MNT=/mnt/sdh
umount $DEV &> /dev/null
mkfs.btrfs -f $DEV
mount $DEV $MNT
num_files=50000
num_clones_per_file=50
for ((i = 1; i <= $num_files; i++)); do
xfs_io -f -c "pwrite 0 64K" $MNT/file_$i > /dev/null
echo -ne "\r$i files created..."
done
echo
btrfs subvolume snapshot -r $MNT $MNT/snap1
cloned=0
for ((i = 1; i <= $num_clones_per_file; i++)); do
for ((j = 1; j <= $num_files; j++)); do
cp --reflink=always $MNT/file_$j $MNT/file_${j}_clone_${i}
cloned=$((cloned + 1))
echo -ne "\r$cloned / $((num_files * num_clones_per_file)) clone operations"
done
done
echo
btrfs subvolume snapshot -r $MNT $MNT/snap2
# Unmount and mount again to clear all cached metadata (and data).
umount $DEV
mount $DEV $MNT
start=$(date +%s%N)
btrfs send $MNT/snap2 > /dev/null
end=$(date +%s%N)
dur=$(( (end - start) / 1000000000 ))
echo -e "\nFull send took $dur seconds"
# Unmount and mount again to clear all cached metadata (and data).
umount $DEV
mount $DEV $MNT
start=$(date +%s%N)
btrfs send -p $MNT/snap1 $MNT/snap2 > /dev/null
end=$(date +%s%N)
dur=$(( (end - start) / 1000000000 ))
echo -e "\nIncremental send took $dur seconds"
umount $MNT
Before applying the patchset:
(...)
Full send took 1108 seconds
(...)
Incremental send took 1135 seconds
After applying the whole patchset:
(...)
Full send took 268 seconds (-75.8%)
(...)
Incremental send took 316 seconds (-72.2%)
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
At find_extent_clone() we search twice for the extent item corresponding
to the data extent that the current file extent items points to:
1) Once with a call to extent_from_logical();
2) Once again during backref walking, through iterate_extent_inodes()
which eventually leads to find_parent_nodes() where we will search
again the extent tree for the same extent item.
The extent tree can be huge, so doing this one extra search for every
extent we want to send adds up and it's expensive.
The first call is there since the send code was introduced and it
accomplishes two things:
1) Check that the extent is flagged as a data extent in the extent tree.
But it can not be anything else, otherwise we wouldn't have a file
extent item in the send root pointing to it.
This was probably added to catch bugs in the early days where send was
yet too young and the interaction with everything else was far from
perfect;
2) Check how many direct references there are on the extent, and if
there's too many (more than SEND_MAX_EXTENT_REFS), avoid doing the
backred walking as it may take too long and slowdown send.
So improve on this by having a callback in the backref walking code that
is called when it finds the extent item in the extent tree, and have those
checks done in the callback. When the callback returns anything different
from 0, it stops the backref walking code. This way we do a single search
on the extent tree for the extent item of our data extent.
Also, before this change we were only checking the number of references on
the data extent against SEND_MAX_EXTENT_REFS, but after starting backref
walking we will end up resolving backrefs for extent buffers in the path
from a leaf having a file extent item pointing to our data extent, up to
roots of trees from which the extent buffer is accessible from, due to
shared subtrees resulting from snapshoting. We were therefore allowing for
the possibility for send taking too long due to some node in the path from
the leaf to a root node being shared too many times. After this change we
check for reference counts being greater than SEND_MAX_EXTENT_REFS for
both data extents and metadata extents.
This change is part of a patchset comprised of the following patches:
01/17 btrfs: fix inode list leak during backref walking at resolve_indirect_refs()
02/17 btrfs: fix inode list leak during backref walking at find_parent_nodes()
03/17 btrfs: fix ulist leaks in error paths of qgroup self tests
04/17 btrfs: remove pointless and double ulist frees in error paths of qgroup tests
05/17 btrfs: send: avoid unnecessary path allocations when finding extent clone
06/17 btrfs: send: update comment at find_extent_clone()
07/17 btrfs: send: drop unnecessary backref context field initializations
08/17 btrfs: send: avoid unnecessary backref lookups when finding clone source
09/17 btrfs: send: optimize clone detection to increase extent sharing
10/17 btrfs: use a single argument for extent offset in backref walking functions
11/17 btrfs: use a structure to pass arguments to backref walking functions
12/17 btrfs: reuse roots ulist on each leaf iteration for iterate_extent_inodes()
13/17 btrfs: constify ulist parameter of ulist_next()
14/17 btrfs: send: cache leaf to roots mapping during backref walking
15/17 btrfs: send: skip unnecessary backref iterations
16/17 btrfs: send: avoid double extent tree search when finding clone source
17/17 btrfs: send: skip resolution of our own backref when finding clone source
Performance test results are in the changelog of patch 17/17.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
When looking for a clone source for an extent, we are iterating over all
the backreferences for an extent. This is often a waste of time, because
once we find a good clone source we could stop immediately instead of
continuing backref walking, which is expensive.
Basically what happens currently is this:
1) Call iterate_extent_inodes() to iterate over all the backreferences;
2) It calls btrfs_find_all_leafs() which in turn calls the main function
to walk over backrefs and collect them - find_parent_nodes();
3) Then we collect all the references for our target data extent from the
extent tree (and delayed refs if any), add them to the rb trees,
resolve all the indirect backreferences and search for all the file
extent items in fs trees, building a list of inodes for each one of
them (struct extent_inode_elem);
4) Then back at iterate_extent_inodes() we find all the roots associated
to each found leaf, and call the callback __iterate_backrefs defined
at send.c for each inode in the inode list associated to each leaf.
Some times one the first backreferences we find in a fs tree is optimal
to satisfy the clone operation that send wants to perform, and in that
case we could stop immediately and avoid resolving all the remaining
indirect backreferences (search fs trees for the respective file extent
items, etc). This possibly if when we find a fs tree leaf with a file
extent item we are able to know what are all the roots that can lead to
the leaf - this is now possible after the previous patch in the series
that adds a cache that maps leaves to a list of roots. So we can now
shortcircuit backref walking during send, by having the callback we
pass to iterate_extent_inodes() to be called when we find a file extent
item for an indirect backreference, and have it return a special value
when it found a suitable backreference and it does not need to look for
more backreferences. This change does that.
This change is part of a patchset comprised of the following patches:
01/17 btrfs: fix inode list leak during backref walking at resolve_indirect_refs()
02/17 btrfs: fix inode list leak during backref walking at find_parent_nodes()
03/17 btrfs: fix ulist leaks in error paths of qgroup self tests
04/17 btrfs: remove pointless and double ulist frees in error paths of qgroup tests
05/17 btrfs: send: avoid unnecessary path allocations when finding extent clone
06/17 btrfs: send: update comment at find_extent_clone()
07/17 btrfs: send: drop unnecessary backref context field initializations
08/17 btrfs: send: avoid unnecessary backref lookups when finding clone source
09/17 btrfs: send: optimize clone detection to increase extent sharing
10/17 btrfs: use a single argument for extent offset in backref walking functions
11/17 btrfs: use a structure to pass arguments to backref walking functions
12/17 btrfs: reuse roots ulist on each leaf iteration for iterate_extent_inodes()
13/17 btrfs: constify ulist parameter of ulist_next()
14/17 btrfs: send: cache leaf to roots mapping during backref walking
15/17 btrfs: send: skip unnecessary backref iterations
16/17 btrfs: send: avoid double extent tree search when finding clone source
17/17 btrfs: send: skip resolution of our own backref when finding clone source
Performance test results are in the changelog of patch 17/17.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
During a send operation, when doing backref walking to determine which
inodes/offsets/roots we can clone from, the most repetitive and expensive
step is to map each leaf that has file extent items pointing to the target
data extent to the IDs of the roots from which the leaves are accessible,
which happens at iterate_extent_inodes(). That step requires finding every
parent node of a leaf, then the parent of each parent, and so on until we
reach a root node. So it's a naturally expensive operation, and repetitive
because each leaf can have hundreds of file extent items (for a nodesize
of 16K, that can be slightly over 200 file extent items). There's also
temporal locality, as we process all file extent items from a leave before
moving the next leaf.
This change caches the mapping of leaves to root IDs, to avoid repeating
those computations over and over again. The cache is limited to a maximum
of 128 entries, with each entry being a struct with a size of 128 bytes,
so the maximum cache size is 16K plus any nodes internally allocated by
the maple tree that is used to index pointers to those structs. The cache
is invalidated whenever we detect relocation happened since we started
filling the cache, because if relocation happened then extent buffers for
leaves and nodes of the trees used by a send operation may have been
reallocated.
This cache also allows for another important optimization that is
introduced in the next patch in the series.
This change is part of a patchset comprised of the following patches:
01/17 btrfs: fix inode list leak during backref walking at resolve_indirect_refs()
02/17 btrfs: fix inode list leak during backref walking at find_parent_nodes()
03/17 btrfs: fix ulist leaks in error paths of qgroup self tests
04/17 btrfs: remove pointless and double ulist frees in error paths of qgroup tests
05/17 btrfs: send: avoid unnecessary path allocations when finding extent clone
06/17 btrfs: send: update comment at find_extent_clone()
07/17 btrfs: send: drop unnecessary backref context field initializations
08/17 btrfs: send: avoid unnecessary backref lookups when finding clone source
09/17 btrfs: send: optimize clone detection to increase extent sharing
10/17 btrfs: use a single argument for extent offset in backref walking functions
11/17 btrfs: use a structure to pass arguments to backref walking functions
12/17 btrfs: reuse roots ulist on each leaf iteration for iterate_extent_inodes()
13/17 btrfs: constify ulist parameter of ulist_next()
14/17 btrfs: send: cache leaf to roots mapping during backref walking
15/17 btrfs: send: skip unnecessary backref iterations
16/17 btrfs: send: avoid double extent tree search when finding clone source
17/17 btrfs: send: skip resolution of our own backref when finding clone source
Performance test results are in the changelog of patch 17/17.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
At iterate_extent_inodes() we collect a ulist of leaves for a given extent
with a call to btrfs_find_all_leafs() and then we enter a loop where we
iterate over all the collected leaves. Each iteration of that loop does a
call to btrfs_find_all_roots_safe(), to determine all roots from which a
leaf is accessible, and that results in allocating and releasing a ulist
to store the root IDs.
Instead of allocating and releasing the roots ulist on every iteration,
allocate a ulist before entering the loop and keep using it on each
iteration, reinitializing the ulist at the end of each iteration.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
The public backref walking functions have quite a lot of arguments that
are passed down the call stack to find_parent_nodes(), the core function
of the backref walking code.
The next patches in series will need to add even arguments to these
functions that should be passed not only to find_parent_nodes(), but also
to other functions used by the later (directly or even lower in the call
stack).
So create a structure to hold all these arguments and state used by the
main backref walking function, find_parent_nodes(), and use it as the
argument for the public backref walking functions iterate_extent_inodes(),
btrfs_find_all_leafs() and btrfs_find_all_roots().
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
The interface for find_parent_nodes() has two extent offset related
arguments:
1) One u64 pointer argument for the extent offset;
2) One boolean argument to tell if the extent offset should be ignored or
not.
These are confusing, becase the extent offset pointer can be NULL and in
some cases callers pass a NULL value as a way to tell the backref walking
code to ignore offsets in file extent items (and simply consider all file
extent items that point to the target data extent).
The boolean argument was added in commit c995ab3cda3f ("btrfs: add a flag
to iterate_inodes_from_logical to find all extent refs for uncompressed
extents"), but it was never really necessary, it was enough if it could
find a way to get a NULL value passed to the "extent_item_pos" argument of
find_parent_nodes(). The arguments are also passed to functions called
by find_parent_nodes() and respective helper functions, which further
makes everything more complicated than needed.
Then we have several backref walking related functions that end up calling
find_parent_nodes(), either directly or through some other function that
they call, and for many we have to use an "extent_item_pos" (u64) argument
and a boolean "ignore_offset" argument too.
This is confusing and not really necessary. So use a single argument to
specify the extent offset, as a simple u64 and not as a pointer, but
using a special value of (u64)-1, defined as a documented constant, to
indicate when the extent offset should be ignored.
This is also preparation work for the upcoming patches in the series that
add other arguments to find_parent_nodes() and other related functions
that use it.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
Currently send does not do the best decisions when it comes to decide
between multiple clone sources, which results in clone operations for
partial extent ranges, which has the following disadvantages:
1) We get less shared extents at the destination;
2) We have to read more data during the send operation and emit more
write commands.
Besides not being optimal behaviour, it also breaks user expectations and
is often reported by users, with a recent example in the Link tag at the
bottom of this change log.
Part of the reason for this non-optimal behaviour is that the backref
walking code does not provide information about the length of the file
extent items that were found for each backref, so send is blind about
which backref is the best to chose as a cloning source.
The other existing reasons are just silliness, namely always prefering
the inode with the lowest number when multiple are found for the same
root and when we can clone from multiple roots, always prefer the send
root over any of the other clone roots. This does not make any sense
since any inode or root is fine and as good as any other inode/root.
Fix this by making backref walking pass information about the number of
bytes referenced by each file extent item and then have send's backref
callback pick the inode with the highest number of bytes for each root.
Finally select the root from which we can clone more bytes from.
Example reproducer:
$ cat test.sh
#!/bin/bash
DEV=/dev/sdi
MNT=/mnt/sdi
mkfs.btrfs -f $DEV
mount $DEV $MNT
xfs_io -f -c "pwrite -S 0xab -b 2M 0 2M" $MNT/foo
cp --reflink=always $MNT/foo $MNT/bar
cp --reflink=always $MNT/foo $MNT/baz
sync
# Overwrite the second half of file foo.
xfs_io -c "pwrite -S 0xcd -b 1M 1M 1M" $MNT/foo
sync
echo
echo "*** fiemap in the original filesystem ***"
echo
xfs_io -c "fiemap -v" $MNT/foo
xfs_io -c "fiemap -v" $MNT/bar
xfs_io -c "fiemap -v" $MNT/baz
echo
btrfs filesystem du $MNT
btrfs subvolume snapshot -r $MNT $MNT/snap
btrfs send -f /tmp/send_stream $MNT/snap
umount $MNT
mkfs.btrfs -f $DEV &> /dev/null
mount $DEV $MNT
btrfs receive -f /tmp/send_stream $MNT
echo
echo "*** fiemap in the new filesystem ***"
echo
xfs_io -r -c "fiemap -v" $MNT/snap/foo
xfs_io -r -c "fiemap -v" $MNT/snap/bar
xfs_io -r -c "fiemap -v" $MNT/snap/baz
echo
btrfs filesystem du $MNT
rm -f /tmp/send_stream
rm -f /tmp/snap.fssum
umount $MNT
Before this change:
$ ./test.sh
(...)
*** fiemap in the original filesystem ***
/mnt/sdi/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..2047]: 26624..28671 2048 0x2000
1: [2048..4095]: 30720..32767 2048 0x1
/mnt/sdi/bar:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..4095]: 26624..30719 4096 0x2001
/mnt/sdi/baz:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..4095]: 26624..30719 4096 0x2001
Total Exclusive Set shared Filename
2.00MiB 1.00MiB - /mnt/sdi/foo
2.00MiB 0.00B - /mnt/sdi/bar
2.00MiB 0.00B - /mnt/sdi/baz
6.00MiB 1.00MiB 2.00MiB /mnt/sdi
Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap'
At subvol /mnt/sdi/snap
At subvol snap
*** fiemap in the new filesystem ***
/mnt/sdi/snap/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..4095]: 26624..30719 4096 0x2001
/mnt/sdi/snap/bar:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..2047]: 26624..28671 2048 0x2000
1: [2048..4095]: 30720..32767 2048 0x1
/mnt/sdi/snap/baz:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..2047]: 26624..28671 2048 0x2000
1: [2048..4095]: 32768..34815 2048 0x1
Total Exclusive Set shared Filename
2.00MiB 0.00B - /mnt/sdi/snap/foo
2.00MiB 1.00MiB - /mnt/sdi/snap/bar
2.00MiB 1.00MiB - /mnt/sdi/snap/baz
6.00MiB 2.00MiB - /mnt/sdi/snap
6.00MiB 2.00MiB 2.00MiB /mnt/sdi
We end up with two 1M extents that are not shared for files bar and baz.
After this change:
$ ./test.sh
(...)
*** fiemap in the original filesystem ***
/mnt/sdi/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..2047]: 26624..28671 2048 0x2000
1: [2048..4095]: 30720..32767 2048 0x1
/mnt/sdi/bar:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..4095]: 26624..30719 4096 0x2001
/mnt/sdi/baz:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..4095]: 26624..30719 4096 0x2001
Total Exclusive Set shared Filename
2.00MiB 1.00MiB - /mnt/sdi/foo
2.00MiB 0.00B - /mnt/sdi/bar
2.00MiB 0.00B - /mnt/sdi/baz
6.00MiB 1.00MiB 2.00MiB /mnt/sdi
Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap'
At subvol /mnt/sdi/snap
At subvol snap
*** fiemap in the new filesystem ***
/mnt/sdi/snap/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..4095]: 26624..30719 4096 0x2001
/mnt/sdi/snap/bar:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..2047]: 26624..28671 2048 0x2000
1: [2048..4095]: 30720..32767 2048 0x2001
/mnt/sdi/snap/baz:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..2047]: 26624..28671 2048 0x2000
1: [2048..4095]: 30720..32767 2048 0x2001
Total Exclusive Set shared Filename
2.00MiB 0.00B - /mnt/sdi/snap/foo
2.00MiB 0.00B - /mnt/sdi/snap/bar
2.00MiB 0.00B - /mnt/sdi/snap/baz
6.00MiB 0.00B - /mnt/sdi/snap
6.00MiB 0.00B 3.00MiB /mnt/sdi
Now there's a much better sharing, files bar and baz share 1M of the
extent of file foo and the second extent of files bar and baz is shared
between themselves.
This will later be turned into a test case for fstests.
Link: https://lore.kernel.org/linux-btrfs/20221008005704.795b44b0@crass-HP-ZBook-15-G2/
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Move these out of ctree.h into relocation.h to cut down on code in
ctree.h
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Move all the extent tree related prototypes to extent-tree.h out of
ctree.h, and then go include it everywhere needed so everything
compiles.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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There's only one caller that passes GFP_NOFS, we can drop the parameter
an use the flags directly.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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This is a large patch, but because they're all macros it's impossible to
split up. Simply copy all of the item accessors in ctree.h and paste
them in accessors.h, and then update any files to include the header so
everything compiles.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ reformat comments, style fixups ]
Signed-off-by: David Sterba <dsterba@suse.com>
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We have several fs wide related helpers in ctree.h. The bulk of these
are the incompat flag test helpers, but there are things such as
btrfs_fs_closing() and the read only helpers that also aren't directly
related to the ctree code. Move these into a fs.h header, which will
serve as the location for file system wide related helpers.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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During fiemap, when determining if a data extent is shared or not, if we
don't find the extent is directly shared, then we need to determine if
it's shared through subtrees. For that we need to resolve the indirect
reference we found in order to figure out the path in the inode's fs tree,
which is a path starting at the fs tree's root node and going down to the
leaf that contains the file extent item that points to the data extent.
We then proceed to determine if any extent buffer in that path is shared
with other trees or not.
However when the generation of the data extent is more recent than the
last generation used to snapshot the root, we don't need to determine
the path, since the data extent can not be shared through snapshots.
For this case we currently still determine the leaf of that path (at
find_parent_nodes(), but then stop determining the other nodes in the
path (at btrfs_is_data_extent_shared()) as it's pointless.
So do the check of the data extent's generation earlier, at
find_parent_nodes(), before trying to resolve the indirect reference to
determine the leaf in the path. This saves us from doing one expensive
b+tree search in the fs tree of our target inode, as well as other minor
work.
The following test was run on a non-debug kernel (Debian's default kernel
config):
$ cat test-fiemap.sh
#!/bin/bash
DEV=/dev/sdi
MNT=/mnt/sdi
umount $DEV &> /dev/null
mkfs.btrfs -f $DEV
# Use compression to quickly create files with a lot of extents
# (each with a size of 128K).
mount -o compress=lzo $DEV $MNT
# 40G gives 327680 extents, each with a size of 128K.
xfs_io -f -c "pwrite -S 0xab -b 1M 0 40G" $MNT/foobar
# Add some more files to increase the size of the fs and extent
# trees (in the real world there's a lot of files and extents
# from other files).
xfs_io -f -c "pwrite -S 0xcd -b 1M 0 20G" $MNT/file1
xfs_io -f -c "pwrite -S 0xef -b 1M 0 20G" $MNT/file2
xfs_io -f -c "pwrite -S 0x73 -b 1M 0 20G" $MNT/file3
umount $MNT
mount -o compress=lzo $DEV $MNT
start=$(date +%s%N)
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds (metadata not cached)"
echo
start=$(date +%s%N)
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds (metadata cached)"
umount $MNT
Before applying this patch:
(...)
/mnt/sdi/foobar: 327680 extents found
fiemap took 1285 milliseconds (metadata not cached)
/mnt/sdi/foobar: 327680 extents found
fiemap took 742 milliseconds (metadata cached)
After applying this patch:
(...)
/mnt/sdi/foobar: 327680 extents found
fiemap took 689 milliseconds (metadata not cached)
/mnt/sdi/foobar: 327680 extents found
fiemap took 393 milliseconds (metadata cached)
That's a -46.4% total reduction for the metadata not cached case, and
a -47.0% reduction for the cached metadata case.
The test is somewhat limited in the sense the gains may be higher in
practice, because in the test the filesystem is small, so we have small
fs and extent trees, plus there's no concurrent access to the trees as
well, therefore no lock contention there.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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During fiemap, when determining if a data extent is shared or not, if we
don't find the extent is directly shared, then we need to determine if
it's shared through subtrees. For that we need to resolve the indirect
reference we found in order to figure out the path in the inode's fs tree,
which is a path starting at the fs tree's root node and going down to the
leaf that contains the file extent item that points to the data extent.
We then proceed to determine if any extent buffer in that path is shared
with other trees or not.
Currently whenever we find the data extent that a file extent item points
to is not directly shared, we always resolve the path in the fs tree, and
then check if any extent buffer in the path is shared. This is a lot of
work and when we have file extent items that belong to the same leaf, we
have the same path, so we only need to calculate it once.
This change does that, it keeps track of the current and previous leaf,
and when we find that a data extent is not directly shared, we try to
compute the fs tree path only once and then use it for every other file
extent item in the same leaf, using the existing cached path result for
the leaf as long as the cache results are valid.
This saves us from doing expensive b+tree searches in the fs tree of our
target inode, as well as other minor work.
The following test was run on a non-debug kernel (Debian's default kernel
config):
$ cat test-with-snapshots.sh
#!/bin/bash
DEV=/dev/sdi
MNT=/mnt/sdi
umount $DEV &> /dev/null
mkfs.btrfs -f $DEV
# Use compression to quickly create files with a lot of extents
# (each with a size of 128K).
mount -o compress=lzo $DEV $MNT
# 40G gives 327680 extents, each with a size of 128K.
xfs_io -f -c "pwrite -S 0xab -b 1M 0 40G" $MNT/foobar
# Add some more files to increase the size of the fs and extent
# trees (in the real world there's a lot of files and extents
# from other files).
xfs_io -f -c "pwrite -S 0xcd -b 1M 0 20G" $MNT/file1
xfs_io -f -c "pwrite -S 0xef -b 1M 0 20G" $MNT/file2
xfs_io -f -c "pwrite -S 0x73 -b 1M 0 20G" $MNT/file3
# Create a snapshot so all the extents become indirectly shared
# through subtrees, with a generation less than or equals to the
# generation used to create the snapshot.
btrfs subvolume snapshot -r $MNT $MNT/snap1
umount $MNT
mount -o compress=lzo $DEV $MNT
start=$(date +%s%N)
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds (metadata not cached)"
echo
start=$(date +%s%N)
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds (metadata cached)"
umount $MNT
Result before applying this patch:
(...)
/mnt/sdi/foobar: 327680 extents found
fiemap took 1204 milliseconds (metadata not cached)
/mnt/sdi/foobar: 327680 extents found
fiemap took 729 milliseconds (metadata cached)
Result after applying this patch:
(...)
/mnt/sdi/foobar: 327680 extents found
fiemap took 732 milliseconds (metadata not cached)
/mnt/sdi/foobar: 327680 extents found
fiemap took 421 milliseconds (metadata cached)
That's a -46.1% total reduction for the metadata not cached case, and
a -42.2% reduction for the cached metadata case.
The test is somewhat limited in the sense the gains may be higher in
practice, because in the test the filesystem is small, so we have small
fs and extent trees, plus there's no concurrent access to the trees as
well, therefore no lock contention there.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Move the static functions to lookup and store sharedness check of an
extent buffer to a location above find_all_parents(), because in the
next patch the lookup function will be used by find_all_parents().
The store function is also moved just because it's the counter part
to the lookup function and it's best to have their definitions close
together.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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During fiemap we process all the file extent items of an inode, by their
file offset order (left to right b+tree order), and then check if the data
extent they point at is shared or not. Until now we didn't cache those
results, we only did it for b+tree nodes/leaves since for each unique
b+tree path we have access to hundreds of file extent items. However, it
is also common to repeat checking the sharedness of a particular data
extent in a very short time window, and the cases that lead to that are
the following:
1) COW writes.
If have a file extent item like this:
[ bytenr X, offset = 0, num_bytes = 512K ]
file offset 0 512K
Then a 4K write into file offset 64K happens, we end up with the
following file extent item layout:
[ bytenr X, offset = 0, num_bytes = 64K ]
file offset 0 64K
[ bytenr Y, offset = 0, num_bytes = 4K ]
file offset 64K 68K
[ bytenr X, offset = 68K, num_bytes = 444K ]
file offset 68K 512K
So during fiemap we well check for the sharedness of the data extent
with bytenr X twice. Typically for COW writes and for at least
moderately updated files, we end up with many file extent items that
point to different sections of the same data extent.
2) Writing into a NOCOW file after a snapshot is taken.
This happens if the target extent was created in a generation older
than the generation where the last snapshot for the root (the tree the
inode belongs to) was made.
This leads to a scenario like the previous one.
3) Writing into sections of a preallocated extent.
For example if a file has the following layout:
[ bytenr X, offset = 0, num_bytes = 1M, type = prealloc ]
0 1M
After doing a 4K write into file offset 0 and another 4K write into
offset 512K, we get the following layout:
[ bytenr X, offset = 0, num_bytes = 4K, type = regular ]
0 4K
[ bytenr X, offset = 4K, num_bytes = 508K, type = prealloc ]
4K 512K
[ bytenr X, offset = 512K, num_bytes = 4K, type = regular ]
512K 516K
[ bytenr X, offset = 516K, num_bytes = 508K, type = prealloc ]
516K 1M
So we end up with 4 consecutive file extent items pointing to the data
extent at bytenr X.
4) Hole punching in the middle of an extent.
For example if a file has the following file extent item:
[ bytenr X, offset = 0, num_bytes = 8M ]
0 8M
And then hole is punched for the file range [4M, 6M[, we our file
extent item split into two:
[ bytenr X, offset = 0, num_bytes = 4M ]
0 4M
[ 2M hole, implicit or explicit depending on NO_HOLES feature ]
4M 6M
[ bytenr X, offset = 6M, num_bytes = 2M ]
6M 8M
Again, we end up with two file extent items pointing to the same
data extent.
5) When reflinking (clone and deduplication) within the same file.
This is probably the least common case of all.
In cases 1, 2, 4 and 4, when we have multiple file extent items that point
to the same data extent, their distance is usually short, typically
separated by a few slots in a b+tree leaf (or across sibling leaves). For
case 5, the distance can vary a lot, but it's typically the less common
case.
This change caches the result of the sharedness checks for data extents,
but only for the last 8 extents that we notice that our inode refers to
with multiple file extent items. Whenever we want to check if a data
extent is shared, we lookup the cache which consists of doing a linear
scan of an 8 elements array, and if we find the data extent there, we
return the result and don't check the extent tree and delayed refs.
The array/cache is small so that doing the search has no noticeable
negative impact on the performance in case we don't have file extent items
within a distance of 8 slots that point to the same data extent.
Slots in the cache/array are overwritten in a simple round robin fashion,
as that approach fits very well.
Using this simple approach with only the last 8 data extents seen is
effective as usually when multiple file extents items point to the same
data extent, their distance is within 8 slots. It also uses very little
memory and the time to cache a result or lookup the cache is negligible.
The following test was run on non-debug kernel (Debian's default kernel
config) to measure the impact in the case of COW writes (first example
given above), where we run fiemap after overwriting 33% of the blocks of
a file:
$ cat test.sh
#!/bin/bash
DEV=/dev/sdi
MNT=/mnt/sdi
umount $DEV &> /dev/null
mkfs.btrfs -f $DEV
mount $DEV $MNT
FILE_SIZE=$((1 * 1024 * 1024 * 1024))
# Create the file full of 1M extents.
xfs_io -f -s -c "pwrite -b 1M -S 0xab 0 $FILE_SIZE" $MNT/foobar
block_count=$((FILE_SIZE / 4096))
# Overwrite about 33% of the file blocks.
overwrite_count=$((block_count / 3))
echo -e "\nOverwriting $overwrite_count 4K blocks (out of $block_count)..."
RANDOM=123
for ((i = 1; i <= $overwrite_count; i++)); do
off=$(((RANDOM % block_count) * 4096))
xfs_io -c "pwrite -S 0xcd $off 4K" $MNT/foobar > /dev/null
echo -ne "\r$i blocks overwritten..."
done
echo -e "\n"
# Unmount and mount to clear all cached metadata.
umount $MNT
mount $DEV $MNT
start=$(date +%s%N)
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds"
umount $MNT
Result before applying this patch:
fiemap took 128 milliseconds
Result after applying this patch:
fiemap took 92 milliseconds (-28.1%)
The test is somewhat limited in the sense the gains may be higher in
practice, because in the test the filesystem is small, so we have small
fs and extent trees, plus there's no concurrent access to the trees as
well, therefore no lock contention there.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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At find_parent_nodes(), at its last step, when iterating over all direct
references, we are checking if we have a share context and if we have
a reference with a different root from the one in the share context.
However that logic is pointless because of two reasons:
1) After the previous patch in the series (subject "btrfs: remove roots
ulist when checking data extent sharedness"), the roots argument is
always NULL when using a share check context (struct share_check), so
this code is never triggered;
2) Even before that previous patch, we could not hit this code because
if we had a reference with a root different from the one in our share
context, then we would have exited earlier when doing either of the
following:
- Adding a second direct ref to the direct refs red black tree
resulted in extent_is_shared() returning true when called from
add_direct_ref() -> add_prelim_ref(), after processing delayed
references or while processing references in the extent tree;
- When adding a second reference to the indirect refs red black
tree (same as above, extent_is_shared() returns true);
- If we only have one indirect reference and no direct references,
then when resolving it at resolve_indirect_refs() we immediately
return that the target extent is shared, therefore never reaching
that loop that iterates over all direct references at
find_parent_nodes();
- If we have 1 indirect reference and 1 direct reference, then we
also exit early because extent_is_shared() ends up returning true
when called through add_prelim_ref() (by add_direct_ref() or
add_indirect_ref()) or add_delayed_refs(). Same applies as when
having a combination of direct, indirect and indirect with missing
key references.
This logic had been obsoleted since commit 3ec4d3238ab165 ("btrfs:
allow backref search checks for shared extents"), which introduced the
early exits in case an extent is shared.
So just remove that logic, and assert at find_parent_nodes() that when we
have a share context we don't have a roots ulist and that we haven't found
the extent to be directly shared after processing delayed references and
all references from the extent tree.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Currently btrfs_is_data_extent_shared() is passing a ulist for the roots
argument of find_parent_nodes(), however it does not use that ulist for
anything and for this context that list always ends up with at most one
element.
Since find_parent_nodes() is able to deal with a NULL ulist for its roots
argument, make btrfs_is_data_extent_shared() pass it NULL and avoid the
burden of allocating memory for the unnused roots ulist, initializing it,
releasing it and allocating one struct ulist_node for it during the call
to find_parent_nodes().
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When calling btrfs_is_data_extent_shared() we pass two ulists that were
allocated by the caller. This is because the single caller, fiemap, calls
btrfs_is_data_extent_shared() multiple times and the ulists can be reused,
instead of allocating new ones before each call and freeing them after
each call.
Now that we have a context structure/object that we pass to
btrfs_is_data_extent_shared(), we can move those ulists to it, and hide
their allocation and the context's allocation in a helper function, as
well as the freeing of the ulists and the context object. This allows to
reduce the number of parameters passed to btrfs_is_data_extent_shared(),
the need to pass the ulists from extent_fiemap() to fiemap_process_hole()
and having the caller deal with allocating and releasing the ulists.
Also rename one of the ulists from 'tmp' / 'tmp_ulist' to 'refs', since
that's a much better name as it reflects what the list is used for (and
matching the argument name for find_parent_nodes()).
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Right now we are using a struct btrfs_backref_shared_cache to pass state
across multiple btrfs_is_data_extent_shared() calls. The structure's name
closely follows its current purpose, which is to cache previous checks
for the sharedness of metadata extents. However we will start using the
structure for more things other than caching sharedness checks, so rename
it to struct btrfs_backref_share_check_ctx.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Currently we pass a root and an inode number as arguments for
btrfs_is_data_extent_shared() and the inode number is always from an
inode that belongs to that root (it wouldn't make sense otherwise).
In every context that we call btrfs_is_data_extent_shared() (fiemap only),
we have an inode available, so directly pass the inode to the function
instead of a root and inode number. This reduces the number of parameters
and it makes the function's signature conform to most other functions we
have.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
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When doing backref walking to determine if an extent is shared, we are
testing if the inode number, stored in the 'inum' field of struct
share_check, is 0. However that can never be case, since the all instances
of the structure are created at btrfs_is_data_extent_shared(), which
always initializes it with the inode number from a fs tree (and the number
for any inode from any tree can never be 0). So remove the checks.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
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When doing backref walking to determine if an extent is shared, we are
testing the root_objectid of the given share_check struct is 0, but that
is an impossible case, since btrfs_is_data_extent_shared() always
initializes the root_objectid field with the id of the given root, and
no root can have an objectid of 0. So remove those checks.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
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During backref walking, at find_parent_nodes(), if we are dealing with a
data extent and we get an error while resolving the indirect backrefs, at
resolve_indirect_refs(), or in the while loop that iterates over the refs
in the direct refs rbtree, we end up leaking the inode lists attached to
the direct refs we have in the direct refs rbtree that were not yet added
to the refs ulist passed as argument to find_parent_nodes(). Since they
were not yet added to the refs ulist and prelim_release() does not free
the lists, on error the caller can only free the lists attached to the
refs that were added to the refs ulist, all the remaining refs get their
inode lists never freed, therefore leaking their memory.
Fix this by having prelim_release() always free any attached inode list
to each ref found in the rbtree, and have find_parent_nodes() set the
ref's inode list to NULL once it transfers ownership of the inode list
to a ref added to the refs ulist passed to find_parent_nodes().
Fixes: 86d5f9944252 ("btrfs: convert prelimary reference tracking to use rbtrees")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
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During backref walking, at resolve_indirect_refs(), if we get an error
we jump to the 'out' label and call ulist_free() on the 'parents' ulist,
which frees all the elements in the ulist - however that does not free
any inode lists that may be attached to elements, through the 'aux' field
of a ulist node, so we end up leaking lists if we have any attached to
the unodes.
Fix this by calling free_leaf_list() instead of ulist_free() when we exit
from resolve_indirect_refs(). The static function free_leaf_list() is
moved up for this to be possible and it's slightly simplified by removing
unnecessary code.
Fixes: 3301958b7c1d ("Btrfs: add inodes before dropping the extent lock in find_all_leafs")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
The path cache used during fiemap used to determine the sharedness of
extent buffers in a path from a leaf containing a file extent item
pointing to our data extent up to the root node of the tree, is meant to
be used for a single path. Having a single path is by far the most common
case, and therefore worth to optimize for, but it's possible to actually
have multiple paths because we have 2 or more leaves.
If we have multiple leaves, the 'level' variable keeps getting incremented
in each iteration of the while loop at btrfs_is_data_extent_shared(),
which means we will treat the second leaf in the 'tmp' ulist as a level 1
node, and so forth. In the worst case this can lead to getting a level
greater than or equals to BTRFS_MAX_LEVEL (8), which will trigger a
WARN_ON_ONCE() in the functions to lookup from or store in the path cache
(lookup_backref_shared_cache() and store_backref_shared_cache()). If the
current level never goes beyond 8, due to shared nodes in the paths and
a fs tree height smaller than 8, it can still result in incorrectly
marking one leaf as shared because some other leaf is shared and is stored
one level below that other leaf, as when storing a true sharedness value
in the cache results in updating the sharedness to true of all entries in
the cache below the current level.
Having multiple leaves happens in a case like the following:
- We have a file extent item point to data extent at bytenr X, for
a file range [0, 1M[ for example;
- At this moment we have an extent data ref for the extent, with
an offset of 0 and a count of 1;
- A write into the middle of the extent happens, file range [64K, 128K)
so the file extent item is split into two (at btrfs_drop_extents()):
1) One for file range [0, 64K), with a length (num_bytes field) of
64K and an extent offset of 0;
2) Another one for file range [128K, 1M), with a length of 896K
(1M - 128K) and an extent offset of 128K.
- At this moment the two file extent items are located in the same
leaf;
- A new file extent item for the range [64K, 128K), pointing to a new
data extent, is inserted in the leaf. This results in a leaf split
and now those two file extent items pointing to data extent X end
up located in different leaves;
- Once delayed refs are run, we still have a single extent data ref
item for our data extent at bytenr X, for offset 0, but now with a
count of 2 instead of 1;
- So during fiemap, at btrfs_is_data_extent_shared(), after we call
find_parent_nodes() for the data extent, we get two leaves, since
we have two file extent items point to data extent at bytenr X that
are located in two different leaves.
So skip the use of the path cache when we get more than one leaf.
Fixes: 12a824dc67a61e ("btrfs: speedup checking for extent sharedness during fiemap")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
During backref walking, when processing a delayed reference with a type of
BTRFS_TREE_BLOCK_REF_KEY, we have two bugs there:
1) We are accessing the delayed references extent_op, and its key, without
the protection of the delayed ref head's lock;
2) If there's no extent op for the delayed ref head, we end up with an
uninitialized key in the stack, variable 'tmp_op_key', and then pass
it to add_indirect_ref(), which adds the reference to the indirect
refs rb tree.
This is wrong, because indirect references should have a NULL key
when we don't have access to the key, and in that case they should be
added to the indirect_missing_keys rb tree and not to the indirect rb
tree.
This means that if have BTRFS_TREE_BLOCK_REF_KEY delayed ref resulting
from freeing an extent buffer, therefore with a count of -1, it will
not cancel out the corresponding reference we have in the extent tree
(with a count of 1), since both references end up in different rb
trees.
When using fiemap, where we often need to check if extents are shared
through shared subtrees resulting from snapshots, it means we can
incorrectly report an extent as shared when it's no longer shared.
However this is temporary because after the transaction is committed
the extent is no longer reported as shared, as running the delayed
reference results in deleting the tree block reference from the extent
tree.
Outside the fiemap context, the result is unpredictable, as the key was
not initialized but it's used when navigating the rb trees to insert
and search for references (prelim_ref_compare()), and we expect all
references in the indirect rb tree to have valid keys.
The following reproducer triggers the second bug:
$ cat test.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
mkfs.btrfs -f $DEV
mount -o compress $DEV $MNT
# With a compressed 128M file we get a tree height of 2 (level 1 root).
xfs_io -f -c "pwrite -b 1M 0 128M" $MNT/foo
btrfs subvolume snapshot $MNT $MNT/snap
# Fiemap should output 0x2008 in the flags column.
# 0x2000 means shared extent
# 0x8 means encoded extent (because it's compressed)
echo
echo "fiemap after snapshot, range [120M, 120M + 128K):"
xfs_io -c "fiemap -v 120M 128K" $MNT/foo
echo
# Overwrite one extent and fsync to flush delalloc and COW a new path
# in the snapshot's tree.
#
# After this we have a BTRFS_DROP_DELAYED_REF delayed ref of type
# BTRFS_TREE_BLOCK_REF_KEY with a count of -1 for every COWed extent
# buffer in the path.
#
# In the extent tree we have inline references of type
# BTRFS_TREE_BLOCK_REF_KEY, with a count of 1, for the same extent
# buffers, so they should cancel each other, and the extent buffers in
# the fs tree should no longer be considered as shared.
#
echo "Overwriting file range [120M, 120M + 128K)..."
xfs_io -c "pwrite -b 128K 120M 128K" $MNT/snap/foo
xfs_io -c "fsync" $MNT/snap/foo
# Fiemap should output 0x8 in the flags column. The extent in the range
# [120M, 120M + 128K) is no longer shared, it's now exclusive to the fs
# tree.
echo
echo "fiemap after overwrite range [120M, 120M + 128K):"
xfs_io -c "fiemap -v 120M 128K" $MNT/foo
echo
umount $MNT
Running it before this patch:
$ ./test.sh
(...)
wrote 134217728/134217728 bytes at offset 0
128 MiB, 128 ops; 0.1152 sec (1.085 GiB/sec and 1110.5809 ops/sec)
Create a snapshot of '/mnt/sdj' in '/mnt/sdj/snap'
fiemap after snapshot, range [120M, 120M + 128K):
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [245760..246015]: 34304..34559 256 0x2008
Overwriting file range [120M, 120M + 128K)...
wrote 131072/131072 bytes at offset 125829120
128 KiB, 1 ops; 0.0001 sec (683.060 MiB/sec and 5464.4809 ops/sec)
fiemap after overwrite range [120M, 120M + 128K):
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [245760..246015]: 34304..34559 256 0x2008
The extent in the range [120M, 120M + 128K) is still reported as shared
(0x2000 bit set) after overwriting that range and flushing delalloc, which
is not correct - an entire path was COWed in the snapshot's tree and the
extent is now only referenced by the original fs tree.
Running it after this patch:
$ ./test.sh
(...)
wrote 134217728/134217728 bytes at offset 0
128 MiB, 128 ops; 0.1198 sec (1.043 GiB/sec and 1068.2067 ops/sec)
Create a snapshot of '/mnt/sdj' in '/mnt/sdj/snap'
fiemap after snapshot, range [120M, 120M + 128K):
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [245760..246015]: 34304..34559 256 0x2008
Overwriting file range [120M, 120M + 128K)...
wrote 131072/131072 bytes at offset 125829120
128 KiB, 1 ops; 0.0001 sec (694.444 MiB/sec and 5555.5556 ops/sec)
fiemap after overwrite range [120M, 120M + 128K):
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [245760..246015]: 34304..34559 256 0x8
Now the extent is not reported as shared anymore.
So fix this by passing a NULL key pointer to add_indirect_ref() when
processing a delayed reference for a tree block if there's no extent op
for our delayed ref head with a defined key. Also access the extent op
only after locking the delayed ref head's lock.
The reproducer will be converted later to a test case for fstests.
Fixes: 86d5f994425252 ("btrfs: convert prelimary reference tracking to use rbtrees")
Fixes: a6dbceafb915e8 ("btrfs: Remove unused op_key var from add_delayed_refs")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
When processing delayed data references during backref walking and we are
using a share context (we are being called through fiemap), whenever we
find a delayed data reference for an inode different from the one we are
interested in, then we immediately exit and consider the data extent as
shared. This is wrong, because:
1) This might be a DROP reference that will cancel out a reference in the
extent tree;
2) Even if it's an ADD reference, it may be followed by a DROP reference
that cancels it out.
In either case we should not exit immediately.
Fix this by never exiting when we find a delayed data reference for
another inode - instead add the reference and if it does not cancel out
other delayed reference, we will exit early when we call
extent_is_shared() after processing all delayed references. If we find
a drop reference, then signal the code that processes references from
the extent tree (add_inline_refs() and add_keyed_refs()) to not exit
immediately if it finds there a reference for another inode, since we
have delayed drop references that may cancel it out. In this later case
we exit once we don't have references in the rb trees that cancel out
each other and have two references for different inodes.
Example reproducer for case 1):
$ cat test-1.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
mkfs.btrfs -f $DEV
mount $DEV $MNT
xfs_io -f -c "pwrite 0 64K" $MNT/foo
cp --reflink=always $MNT/foo $MNT/bar
echo
echo "fiemap after cloning:"
xfs_io -c "fiemap -v" $MNT/foo
rm -f $MNT/bar
echo
echo "fiemap after removing file bar:"
xfs_io -c "fiemap -v" $MNT/foo
umount $MNT
Running it before this patch, the extent is still listed as shared, it has
the flag 0x2000 (FIEMAP_EXTENT_SHARED) set:
$ ./test-1.sh
fiemap after cloning:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
fiemap after removing file bar:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
Example reproducer for case 2):
$ cat test-2.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
mkfs.btrfs -f $DEV
mount $DEV $MNT
xfs_io -f -c "pwrite 0 64K" $MNT/foo
cp --reflink=always $MNT/foo $MNT/bar
# Flush delayed references to the extent tree and commit current
# transaction.
sync
echo
echo "fiemap after cloning:"
xfs_io -c "fiemap -v" $MNT/foo
rm -f $MNT/bar
echo
echo "fiemap after removing file bar:"
xfs_io -c "fiemap -v" $MNT/foo
umount $MNT
Running it before this patch, the extent is still listed as shared, it has
the flag 0x2000 (FIEMAP_EXTENT_SHARED) set:
$ ./test-2.sh
fiemap after cloning:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
fiemap after removing file bar:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
After this patch, after deleting bar in both tests, the extent is not
reported with the 0x2000 flag anymore, it gets only the flag 0x1
(which is FIEMAP_EXTENT_LAST):
$ ./test-1.sh
fiemap after cloning:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
fiemap after removing file bar:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x1
$ ./test-2.sh
fiemap after cloning:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
fiemap after removing file bar:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x1
These tests will later be converted to a test case for fstests.
Fixes: dc046b10c8b7d4 ("Btrfs: make fiemap not blow when you have lots of snapshots")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
When looking the stored result for a cached path node, if the stored
result is valid and has a value of true, we must update all the nodes for
all levels below it with a result of true as well. This is necessary when
moving from one leaf in the fs tree to the next one, as well as when
moving from a node at any level to the next node at the same level.
Currently this logic is missing as it was somehow forgotten by a recent
patch with the subject: "btrfs: speedup checking for extent sharedness
during fiemap".
This adds the missing logic, which is the counter part to what we do
when adding a shared node to the cache at store_backref_shared_cache().
Fixes: 12a824dc67a6 ("btrfs: speedup checking for extent sharedness during fiemap")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
During fiemap, for each file extent we find, we must check if it's shared
or not. The sharedness check starts by verifying if the extent is directly
shared (its refcount in the extent tree is > 1), and if it is not directly
shared, then we will check if every node in the subvolume b+tree leading
from the root to the leaf that has the file extent item (in reverse order),
is shared (through snapshots).
However this second step is not needed if our extent was created in a
transaction more recent than the last transaction where a snapshot of the
inode's root happened, because it can't be shared indirectly (through
shared subtrees) without a snapshot created in a more recent transaction.
So grab the generation of the extent from the extent map and pass it to
btrfs_is_data_extent_shared(), which will skip this second phase when the
generation is more recent than the root's last snapshot value. Note that
we skip this optimization if the extent map is the result of merging 2
or more extent maps, because in this case its generation is the maximum
of the generations of all merged extent maps.
The fact the we use extent maps and they can be merged despite the
underlying extents being distinct (different file extent items in the
subvolume b+tree and different extent items in the extent b+tree), can
result in some bugs when reporting shared extents. But this is a problem
of the current implementation of fiemap relying on extent maps.
One example where we get incorrect results is:
$ cat fiemap-bug.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
mkfs.btrfs -f $DEV
mount $DEV $MNT
# Create a file with two 256K extents.
# Since there is no other write activity, they will be contiguous,
# and their extent maps merged, despite having two distinct extents.
xfs_io -f -c "pwrite -S 0xab 0 256K" \
-c "fsync" \
-c "pwrite -S 0xcd 256K 256K" \
-c "fsync" \
$MNT/foo
# Now clone only the second extent into another file.
xfs_io -f -c "reflink $MNT/foo 256K 0 256K" $MNT/bar
# Filefrag will report a single 512K extent, and say it's not shared.
echo
filefrag -v $MNT/foo
umount $MNT
Running the reproducer:
$ ./fiemap-bug.sh
wrote 262144/262144 bytes at offset 0
256 KiB, 64 ops; 0.0038 sec (65.479 MiB/sec and 16762.7030 ops/sec)
wrote 262144/262144 bytes at offset 262144
256 KiB, 64 ops; 0.0040 sec (61.125 MiB/sec and 15647.9218 ops/sec)
linked 262144/262144 bytes at offset 0
256 KiB, 1 ops; 0.0002 sec (1.034 GiB/sec and 4237.2881 ops/sec)
Filesystem type is: 9123683e
File size of /mnt/sdj/foo is 524288 (128 blocks of 4096 bytes)
ext: logical_offset: physical_offset: length: expected: flags:
0: 0.. 127: 3328.. 3455: 128: last,eof
/mnt/sdj/foo: 1 extent found
We end up reporting that we have a single 512K that is not shared, however
we have two 256K extents, and the second one is shared. Changing the
reproducer to clone instead the first extent into file 'bar', makes us
report a single 512K extent that is shared, which is algo incorrect since
we have two 256K extents and only the first one is shared.
This is z problem that existed before this change, and remains after this
change, as it can't be easily fixed. The next patch in the series reworks
fiemap to primarily use file extent items instead of extent maps (except
for checking for delalloc ranges), with the goal of improving its
scalability and performance, but it also ends up fixing this particular
bug caused by extent map merging.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
One of the most expensive tasks performed during fiemap is to check if
an extent is shared. This task has two major steps:
1) Check if the data extent is shared. This implies checking the extent
item in the extent tree, checking delayed references, etc. If we
find the data extent is directly shared, we terminate immediately;
2) If the data extent is not directly shared (its extent item has a
refcount of 1), then it may be shared if we have snapshots that share
subtrees of the inode's subvolume b+tree. So we check if the leaf
containing the file extent item is shared, then its parent node, then
the parent node of the parent node, etc, until we reach the root node
or we find one of them is shared - in which case we stop immediately.
During fiemap we process the extents of a file from left to right, from
file offset 0 to EOF. This means that we iterate b+tree leaves from left
to right, and has the implication that we keep repeating that second step
above several times for the same b+tree path of the inode's subvolume
b+tree.
For example, if we have two file extent items in leaf X, and the path to
leaf X is A -> B -> C -> X, then when we try to determine if the data
extent referenced by the first extent item is shared, we check if the data
extent is shared - if it's not, then we check if leaf X is shared, if not,
then we check if node C is shared, if not, then check if node B is shared,
if not than check if node A is shared. When we move to the next file
extent item, after determining the data extent is not shared, we repeat
the checks for X, C, B and A - doing all the expensive searches in the
extent tree, delayed refs, etc. If we have thousands of tile extents, then
we keep repeating the sharedness checks for the same paths over and over.
On a file that has no shared extents or only a small portion, it's easy
to see that this scales terribly with the number of extents in the file
and the sizes of the extent and subvolume b+trees.
This change eliminates the repeated sharedness check on extent buffers
by caching the results of the last path used. The results can be used as
long as no snapshots were created since they were cached (for not shared
extent buffers) or no roots were dropped since they were cached (for
shared extent buffers). This greatly reduces the time spent by fiemap for
files with thousands of extents and/or large extent and subvolume b+trees.
Example performance test:
$ cat fiemap-perf-test.sh
#!/bin/bash
DEV=/dev/sdi
MNT=/mnt/sdi
mkfs.btrfs -f $DEV
mount -o compress=lzo $DEV $MNT
# 40G gives 327680 128K file extents (due to compression).
xfs_io -f -c "pwrite -S 0xab -b 1M 0 40G" $MNT/foobar
umount $MNT
mount -o compress=lzo $DEV $MNT
start=$(date +%s%N)
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds (metadata not cached)"
start=$(date +%s%N)
filefrag $MNT/foobar
end=$(date +%s%N)
dur=$(( (end - start) / 1000000 ))
echo "fiemap took $dur milliseconds (metadata cached)"
umount $MNT
Before this patch:
$ ./fiemap-perf-test.sh
(...)
/mnt/sdi/foobar: 327680 extents found
fiemap took 3597 milliseconds (metadata not cached)
/mnt/sdi/foobar: 327680 extents found
fiemap took 2107 milliseconds (metadata cached)
After this patch:
$ ./fiemap-perf-test.sh
(...)
/mnt/sdi/foobar: 327680 extents found
fiemap took 1646 milliseconds (metadata not cached)
/mnt/sdi/foobar: 327680 extents found
fiemap took 698 milliseconds (metadata cached)
That's about 2.2x faster when no metadata is cached, and about 3x faster
when all metadata is cached. On a real filesystem with many other files,
data, directories, etc, the b+trees will be 2 or 3 levels higher,
therefore this optimization will have a higher impact.
Several reports of a slow fiemap show up often, the two Link tags below
refer to two recent reports of such slowness. This patch, together with
the next ones in the series, is meant to address that.
Link: https://lore.kernel.org/linux-btrfs/21dd32c6-f1f9-f44a-466a-e18fdc6788a7@virtuozzo.com/
Link: https://lore.kernel.org/linux-btrfs/Ysace25wh5BbLd5f@atmark-techno.com/
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
The function btrfs_check_shared() is supposed to be used to check if a
data extent is shared, but its name is too generic, may easily cause
confusion in the sense that it may be used for metadata extents.
So rename it to btrfs_is_data_extent_shared(), which will also make it
less confusing after the next change that adds a backref lookup cache for
the b+tree nodes that lead to the leaf that contains the file extent item
that points to the target data extent.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
There's only one function we pass to iterate_inodes_from_logical as
iterator, so we can drop the indirection and call it directly, after
moving the function to backref.c
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
The inode reference iterator interface takes parameters that are derived
from the context parameter, but as it's a void* type the values are
passed individually.
Change the ctx type to inode_fs_path as it's the only thing we pass and
drop any parameters that are derived from that.
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
The functions for iterating inode reference take a function parameter
but there's only one value, inode_to_path(). Remove the indirection and
call the function. As paths_from_inode would become just an alias for
iterate_irefs(), merge the two into one function.
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
We had an error handling pattern for read_tree_block() like this:
eb = read_tree_block();
if (IS_ERR(eb)) {
/*
* Handling error here
* Normally ended up with return or goto out.
*/
} else if (!extent_buffer_uptodate(eb)) {
/*
* Different error handling here
* Normally also ended up with return or goto out;
*/
}
This is fine, but if we want to add extra check for each
read_tree_block(), the existing if-else-if is not that expandable and
will take reader some seconds to figure out there is no extra branch.
Here we change it to a more common way, without the extra else:
eb = read_tree_block();
if (IS_ERR(eb)) {
/*
* Handling error here
*/
return eb or goto out;
}
if (!extent_buffer_uptodate(eb)) {
/*
* Different error handling here
*/
return eb or goto out;
}
This also removes some oddball call sites which uses some creative way
to check error.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
|
When we start having multiple extent roots we'll need to use a helper to
get to the correct extent_root. Rename fs_info->extent_root to
_extent_root and convert all of the users of the extent root to using
the btrfs_extent_root() helper. This will allow us to easily clean up
the remaining direct accesses in the future.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
