btrfs: reduce lock contention when eb cache miss for btree search

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When crawling btree, if an eb cache miss occurs, we change to use the eb
read lock and release all previous locks (including the parent lock) to
reduce lock contention.

If an eb cache miss occurs in a leaf and needs to execute IO, before this
change we released locks only from level 2 and up and we read a leaf's
content from disk while holding a lock on its parent (level 1), causing
the unnecessary lock contention on the parent, after this change we
release locks from level 1 and up, but we lock level 0, and read leaf's
content from disk.

Because we have prepared the check parameters and the read lock of eb we
hold, we can ensure that no race will occur during the check and cause
unexpected errors.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Robbie Ko <robbieko@synology.com>
Signed-off-by: David Sterba <dsterba@suse.com>

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Robbie Ko 2024-10-15 15:41:37 +08:00 • committed by David Sterba

parent a9c50c9756

commit 99785998ed

1 changed files with 70 additions and 31 deletions

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fs/btrfs/ctree.c

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