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authorChris Mason <chris.mason@oracle.com>2009-03-13 17:10:06 +0300
committerChris Mason <chris.mason@oracle.com>2009-03-24 23:14:25 +0300
commit56bec294dea971335d4466b30f2d959f28f6e36d (patch)
treefc0b5bbf4bb6ab35582a4c7f58f5ac88f71c38bf /fs/btrfs/transaction.h
parent9fa8cfe706f9c20067c042a064999d5825a35330 (diff)
downloadlinux-56bec294dea971335d4466b30f2d959f28f6e36d.tar.xz
Btrfs: do extent allocation and reference count updates in the background
The extent allocation tree maintains a reference count and full back reference information for every extent allocated in the filesystem. For subvolume and snapshot trees, every time a block goes through COW, the new copy of the block adds a reference on every block it points to. If a btree node points to 150 leaves, then the COW code needs to go and add backrefs on 150 different extents, which might be spread all over the extent allocation tree. These updates currently happen during btrfs_cow_block, and most COWs happen during btrfs_search_slot. btrfs_search_slot has locks held on both the parent and the node we are COWing, and so we really want to avoid IO during the COW if we can. This commit adds an rbtree of pending reference count updates and extent allocations. The tree is ordered by byte number of the extent and byte number of the parent for the back reference. The tree allows us to: 1) Modify back references in something close to disk order, reducing seeks 2) Significantly reduce the number of modifications made as block pointers are balanced around 3) Do all of the extent insertion and back reference modifications outside of the performance critical btrfs_search_slot code. #3 has the added benefit of greatly reducing the btrfs stack footprint. The extent allocation tree modifications are done without the deep (and somewhat recursive) call chains used in the past. These delayed back reference updates must be done before the transaction commits, and so the rbtree is tied to the transaction. Throttling is implemented to help keep the queue of backrefs at a reasonable size. Since there was a similar mechanism in place for the extent tree extents, that is removed and replaced by the delayed reference tree. Yan Zheng <yan.zheng@oracle.com> helped review and fixup this code. Signed-off-by: Chris Mason <chris.mason@oracle.com>
Diffstat (limited to 'fs/btrfs/transaction.h')
-rw-r--r--fs/btrfs/transaction.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index ea292117f882..94876709217f 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -19,6 +19,7 @@
#ifndef __BTRFS_TRANSACTION__
#define __BTRFS_TRANSACTION__
#include "btrfs_inode.h"
+#include "delayed-ref.h"
struct btrfs_transaction {
u64 transid;
@@ -34,6 +35,7 @@ struct btrfs_transaction {
wait_queue_head_t writer_wait;
wait_queue_head_t commit_wait;
struct list_head pending_snapshots;
+ struct btrfs_delayed_ref_root delayed_refs;
};
struct btrfs_trans_handle {
@@ -44,6 +46,7 @@ struct btrfs_trans_handle {
u64 block_group;
u64 alloc_exclude_start;
u64 alloc_exclude_nr;
+ unsigned long delayed_ref_updates;
};
struct btrfs_pending_snapshot {