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authorChris Mason <chris.mason@oracle.com>2009-02-04 09:27:02 -0500
committerChris Mason <chris.mason@oracle.com>2009-02-04 09:27:02 -0500
commitbd56b30205bc09da0beb80d4ba3d4c7309792da5 (patch)
treea5cb3104687b27e923b73b2840f053abc1229a92 /fs/btrfs/inode.c
parentb4ce94de9b4d64e8ab3cf155d13653c666e22b9b (diff)
Btrfs: Make btrfs_drop_snapshot work in larger and more efficient chunks
Every transaction in btrfs creates a new snapshot, and then schedules the snapshot from the last transaction for deletion. Snapshot deletion works by walking down the btree and dropping the reference counts on each btree block during the walk. If if a given leaf or node has a reference count greater than one, the reference count is decremented and the subtree pointed to by that node is ignored. If the reference count is one, walking continues down into that node or leaf, and the references of everything it points to are decremented. The old code would try to work in small pieces, walking down the tree until it found the lowest leaf or node to free and then returning. This was very friendly to the rest of the FS because it didn't have a huge impact on other operations. But it wouldn't always keep up with the rate that new commits added new snapshots for deletion, and it wasn't very optimal for the extent allocation tree because it wasn't finding leaves that were close together on disk and processing them at the same time. This changes things to walk down to a level 1 node and then process it in bulk. All the leaf pointers are sorted and the leaves are dropped in order based on their extent number. The extent allocation tree and commit code are now fast enough for this kind of bulk processing to work without slowing the rest of the FS down. Overall it does less IO and is better able to keep up with snapshot deletions under high load. Signed-off-by: Chris Mason <chris.mason@oracle.com>
Diffstat (limited to 'fs/btrfs/inode.c')
-rw-r--r--fs/btrfs/inode.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ebd7d6c37df8..95ea58cb3065 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2441,6 +2441,8 @@ next_node:
2441 ref->generation = leaf_gen; 2441 ref->generation = leaf_gen;
2442 ref->nritems = 0; 2442 ref->nritems = 0;
2443 2443
2444 btrfs_sort_leaf_ref(ref);
2445
2444 ret = btrfs_add_leaf_ref(root, ref, 0); 2446 ret = btrfs_add_leaf_ref(root, ref, 0);
2445 WARN_ON(ret); 2447 WARN_ON(ret);
2446 btrfs_free_leaf_ref(root, ref); 2448 btrfs_free_leaf_ref(root, ref);