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Relocation COWs metadata blocks in two cases for the reloc root:
- copying the subvolume root item when creating the reloc root
- copying a btree node when there is a COW during relocation
In both cases, the resulting btree node hits an abnormal code path with
respect to the owner field in its btrfs_header. It first creates the
root item for the new objectid, which populates the reloc root id, and
it at this point that delayed refs are created.
Later, it fully copies the old node into the new node (including the
original owner field) which overwrites it. This results in a simple
quotas mismatch where we run the delayed ref for the reloc root which
has no simple quota effect (reloc root is not an fstree) but when we
ultimately delete the node, the owner is the real original fstree and we
do free the space.
To work around this without tampering with the behavior of relocation,
add a parameter to btrfs_add_tree_block that lets the relocation code
path specify a different owning root than the "operating" root (in this
case, owning root is the real root and the operating root is the reloc
root). These can naturally be plumbed into delayed refs that have the
same concept.
Note that this is a double count in some sense, but a relatively natural
one, as there are really two extents, and the old one will be deleted
soon. This is consistent with how data relocation extents are accounted
by simple quotas.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
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Inline ref parsing is a bit tricky and relies on a decent amount of
implicit information, so I think it is beneficial to have a helper
function for reading the owner ref, if only to "document" the format,
along with the write path.
The main subtlety of note which I was missing by open-coding this was
that it is important to check whether or not inline refs are present
*at all*. i.e., if we are writing out a new extent under squotas, we
will always use a big enough item for the inline ref and have it.
However, it is possible that some random item predating squotas will not
have any inline refs. In that case, trying to read the "type" field of
the first inline ref will just be reading garbage in the form of
whatever is in the next item.
This will be used by the extent free-ing path, which looks up data
extent owners as well as a relocation path which needs to grab the owner
before relocating an extent.
Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When running delayed references, through btrfs_run_delayed_refs(), we can
specify how many to run, run all existing delayed references and keep
running delayed references while we can find any. This is controlled with
the value of the 'count' argument, where a value of 0 means to run all
delayed references that exist by the time btrfs_run_delayed_refs() is
called, (unsigned long)-1 means to keep running delayed references while
we are able find any, and any other value to run that exact number of
delayed references.
Typically a specific value other than 0 or -1 is used when flushing space
to try to release a certain amount of bytes for a ticket. In this case
we just simply calculate how many delayed reference heads correspond to a
specific amount of bytes, with calc_delayed_refs_nr(). However that only
takes into account the space reserved for the reference heads themselves,
and does not account for the space reserved for deleting checksums from
the csum tree (see add_delayed_ref_head() and update_existing_head_ref())
in case we are going to delete a data extent. This means we may end up
running more delayed references than necessary in case we process delayed
references for deleting a data extent.
So change the logic of btrfs_run_delayed_refs() to take a bytes argument
to specify how many bytes of delayed references to run/release, using the
special values of 0 to mean all existing delayed references and U64_MAX
(or (u64)-1) to keep running delayed references while we can find any.
This prevents running more delayed references than necessary, when we have
delayed references for deleting data extents, but also makes the upcoming
changes/patches simpler and it's preparatory work for them.
Reviewed-by: Josef Bacik <josef@toxicpanda.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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Both callers of btrfs_pin_extent_for_log_replay expand the parameters to
extent buffer members. We can simply pass the extent buffer instead.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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There is only one caller of btrfs_pin_reserved_extent that expands the
parameters to extent buffer members. We can simply pass the extent
buffer instead.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Drop all __must_check annotations because they're used in random
functions and not consistently. All errors should be handled.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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extent-tree.h uses btrfs_delayed_ref_head in a function argument but
doesn't pull it's declaration from anywhere, add it to the top of the
header.
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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My initial fix for the generic/475 hangs was related to metadata, but
our CI testing uncovered another case where we hang for similar reasons.
We again have a task with a plug that is holding an outstanding request
that is keeping the dm device from finishing it's suspend, and that task
is stuck in the allocator.
This time it is stuck trying to allocate data, but we do not have a
block group that matches the size class. The larger loop in the
allocator looks like this (simplified of course)
find_free_extent
for_each_block_group {
ffe_ctl->cached == btrfs_block_group_cache_done(bg)
if (!ffe_ctl->cached)
ffe_ctl->have_caching_bg = true;
do_allocation()
btrfs_wait_block_group_cache_progress();
}
if (loop == LOOP_CACHING_WAIT && ffe_ctl->have_caching_bg)
go search again;
In my earlier fix we were trying to allocate from the block group, but
we weren't waiting for the progress because we were only waiting for the
free space to be >= the amount of free space we wanted. My fix made it
so we waited for forward progress to be made as well, so we would be
sure to wait.
This time however we did not have a block group that matched our size
class, so what was happening was this
find_free_extent
for_each_block_group {
ffe_ctl->cached == btrfs_block_group_cache_done(bg)
if (!ffe_ctl->cached)
ffe_ctl->have_caching_bg = true;
if (size_class_doesn't_match())
goto loop;
do_allocation()
btrfs_wait_block_group_cache_progress();
loop:
release_block_group(block_group);
}
if (loop == LOOP_CACHING_WAIT && ffe_ctl->have_caching_bg)
go search again;
The size_class_doesn't_match() part was true, so we'd just skip this
block group and never wait for caching, and then because we found a
caching block group we'd just go back and do the loop again. We never
sleep and thus never flush the plug and we have the same deadlock.
Fix the logic for waiting on the block group caching to instead do it
unconditionally when we goto loop. This takes the logic out of the
allocation step, so now the loop looks more like this
find_free_extent
for_each_block_group {
ffe_ctl->cached == btrfs_block_group_cache_done(bg)
if (!ffe_ctl->cached)
ffe_ctl->have_caching_bg = true;
if (size_class_doesn't_match())
goto loop;
do_allocation()
btrfs_wait_block_group_cache_progress();
loop:
if (loop > LOOP_CACHING_NOWAIT && !ffe_ctl->retry_uncached &&
!ffe_ctl->cached) {
ffe_ctl->retry_uncached = true;
btrfs_wait_block_group_cache_progress();
}
release_block_group(block_group);
}
if (loop == LOOP_CACHING_WAIT && ffe_ctl->have_caching_bg)
go search again;
This simplifies the logic a lot, and makes sure that if we're hitting
uncached block groups we're always waiting on them at some point.
I ran this through 100 iterations of generic/475, as this particular
case was harder to hit than the previous one.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The function btrfs_free_excluded_extents() is only used by block-group.c,
so move it into block-group.c and make it static. Also removed unnecessary
variables that are used only once.
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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The code for btrfs_add_excluded_extent() is trivial, it's just a
set_extent_bit() call. However it's defined in extent-tree.c but it is
only used (twice) in block-group.c. So open code it in block-group.c,
reducing the need to export a trivial function.
Also since the only caller btrfs_add_excluded_extent() is prepared to
deal with errors, stop ignoring errors from the set_extent_bit() call.
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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We just pass in btrfs_header_level(eb) for the level, and we're passing
in the eb already, so simply get the level from the eb inside of
btrfs_set_block_flags.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The aim of this patch is to reduce the fragmentation of block groups
under certain unhappy workloads. It is particularly effective when the
size of extents correlates with their lifetime, which is something we
have observed causing fragmentation in the fleet at Meta.
This patch categorizes extents into size classes:
- x < 128KiB: "small"
- 128KiB < x < 8MiB: "medium"
- x > 8MiB: "large"
and as much as possible reduces allocations of extents into block groups
that don't match the size class. This takes advantage of any (possible)
correlation between size and lifetime and also leaves behind predictable
re-usable gaps when extents are freed; small writes don't gum up bigger
holes.
Size classes are implemented in the following way:
- Mark each new block group with a size class of the first allocation
that goes into it.
- Add two new passes to ffe: "unset size class" and "wrong size class".
First, try only matching block groups, then try unset ones, then allow
allocation of new ones, and finally allow mismatched block groups.
- Filtering is done just by skipping inappropriate ones, there is no
special size class indexing.
Other solutions I considered were:
- A best fit allocator with an rb-tree. This worked well, as small
writes didn't leak big holes from large freed extents, but led to
regressions in ffe and write performance due to lock contention on
the rb-tree with every allocation possibly updating it in parallel.
Perhaps something clever could be done to do the updates in the
background while being "right enough".
- A fixed size "working set". This prevents freeing an extent
drastically changing where writes currently land, and seems like a
good option too. Doesn't take advantage of size in any way.
- The same size class idea, but implemented with xarray marks. This
turned out to be slower than looping the linked list and skipping
wrong block groups, and is also less flexible since we must have only
3 size classes (max #marks). With the current approach we can have as
many as we like.
Performance testing was done via: https://github.com/josefbacik/fsperf
Of particular relevance are the new fragmentation specific tests.
A brief summary of the testing results:
- Neutral results on existing tests. There are some minor regressions
and improvements here and there, but nothing that truly stands out as
notable.
- Improvement on new tests where size class and extent lifetime are
correlated. Fragmentation in these cases is completely eliminated
and write performance is generally a little better. There is also
significant improvement where extent sizes are just a bit larger than
the size class boundaries.
- Regression on one new tests: where the allocations are sized
intentionally a hair under the borders of the size classes. Results
are neutral on the test that intentionally attacks this new scheme by
mixing extent size and lifetime.
The full dump of the performance results can be found here:
https://bur.io/fsperf/size-class-2022-11-15.txt
(there are ANSI escape codes, so best to curl and view in terminal)
Here is a snippet from the full results for a new test which mixes
buffered writes appending to a long lived set of files and large short
lived fallocates:
bufferedappendvsfallocate results
metric baseline current stdev diff
======================================================================================
avg_commit_ms 31.13 29.20 2.67 -6.22%
bg_count 14 15.60 0 11.43%
commits 11.10 12.20 0.32 9.91%
elapsed 27.30 26.40 2.98 -3.30%
end_state_mount_ns 11122551.90 10635118.90 851143.04 -4.38%
end_state_umount_ns 1.36e+09 1.35e+09 12248056.65 -1.07%
find_free_extent_calls 116244.30 114354.30 964.56 -1.63%
find_free_extent_ns_max 599507.20 1047168.20 103337.08 74.67%
find_free_extent_ns_mean 3607.19 3672.11 101.20 1.80%
find_free_extent_ns_min 500 512 6.67 2.40%
find_free_extent_ns_p50 2848 2876 37.65 0.98%
find_free_extent_ns_p95 4916 5000 75.45 1.71%
find_free_extent_ns_p99 20734.49 20920.48 1670.93 0.90%
frag_pct_max 61.67 0 8.05 -100.00%
frag_pct_mean 43.59 0 6.10 -100.00%
frag_pct_min 25.91 0 16.60 -100.00%
frag_pct_p50 42.53 0 7.25 -100.00%
frag_pct_p95 61.67 0 8.05 -100.00%
frag_pct_p99 61.67 0 8.05 -100.00%
fragmented_bg_count 6.10 0 1.45 -100.00%
max_commit_ms 49.80 46 5.37 -7.63%
sys_cpu 2.59 2.62 0.29 1.39%
write_bw_bytes 1.62e+08 1.68e+08 17975843.50 3.23%
write_clat_ns_mean 57426.39 54475.95 2292.72 -5.14%
write_clat_ns_p50 46950.40 42905.60 2101.35 -8.62%
write_clat_ns_p99 148070.40 143769.60 2115.17 -2.90%
write_io_kbytes 4194304 4194304 0 0.00%
write_iops 2476.15 2556.10 274.29 3.23%
write_lat_ns_max 2101667.60 2251129.50 370556.59 7.11%
write_lat_ns_mean 59374.91 55682.00 2523.09 -6.22%
write_lat_ns_min 17353.10 16250 1646.08 -6.36%
There are some mixed improvements/regressions in most metrics along with
an elimination of fragmentation in this workload.
On the balance, the drastic 1->0 improvement in the happy cases seems
worth the mix of regressions and improvements we do observe.
Some considerations for future work:
- Experimenting with more size classes
- More hinting/search ordering work to approximate a best-fit allocator
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
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find_free_extent is a complicated function. It consists (at least) of:
- a hint that jumps into the middle of a for loop macro
- a middle loop trying every raid level
- an outer loop ascending through ffe loop levels
- complicated logic for skipping some of those ffe loop levels
- multiple underlying in-bg allocators (zoned, cluster, no cluster)
Which is all to say that more tracing is helpful for debugging its
behavior. Add two new tracepoints: at the entrance to the block_groups
loop (hit for every raid level and every ffe_ctl loop) and at the point
we seriously consider a block_group for allocation. This way we can see
the whole path through the algorithm, including hints, multiple loops,
etc.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The allocator tracepoints currently have a pile of values from ffe_ctl.
In modifying the allocator and adding more tracepoints, I found myself
adding to the already long argument list of the tracepoints. It makes it
a lot simpler to just send in the ffe_ctl itself.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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These belong in extent-tree.h, they were missed because they were not
grouped with the other extent-tree.c prototypes.
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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btrfs_delayed_extent_op can be packed in a better way, it's 40 bytes now
and has 8 unused bytes. Reducing the level type to u8 makes it possible
to squeeze it to the padding byte after key. The bitfields were switched
to bool as there's space to store the full byte without increasing the
whole structure, besides that the generated assembly is smaller.
struct btrfs_delayed_extent_op {
struct btrfs_disk_key key; /* 0 17 */
u8 level; /* 17 1 */
bool update_key; /* 18 1 */
bool update_flags; /* 19 1 */
bool is_data; /* 20 1 */
/* XXX 3 bytes hole, try to pack */
u64 flags_to_set; /* 24 8 */
/* size: 32, cachelines: 1, members: 6 */
/* sum members: 29, holes: 1, sum holes: 3 */
/* last cacheline: 32 bytes */
};
The final size is 32 bytes which gives +26 object per slab page.
text data bss dec hex filename
938811 43670 23144 1005625 f5839 fs/btrfs/btrfs.ko.before
938747 43670 23144 1005561 f57f9 fs/btrfs/btrfs.ko.after
Signed-off-by: David Sterba <dsterba@suse.com>
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btrfs_qgroup_account_extents().
The new btrfs_qgroup_account_extents() function should be called in
btrfs_commit_transaction() and it will update all the qgroup according
to delayed_ref_root->dirty_extent_root.
The new function can handle both normal operation during
commit_transaction() or in rescan in a unified method with clearer
logic.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
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