[10/19] btrfs: send: use MT_FLAGS_LOCK_EXTERN for the backref cache maple tree

Commit Message

Filipe Manana Jan. 11, 2023, 11:36 a.m. UTC

From: Filipe Manana <[e-mail]>

As send is single threaded and there's no concurrency, we don't need to
protect the accesses to the backref cache's mapple tree, so initialize the
maple tree with the flag MT_FLAGS_LOCK_EXTERN.

This patch is part of a larger patchset and the changelog of the last
patch in the series contains a sample performance test and results.
The patches that comprise the patchset are the following:

  btrfs: send: directly return from did_overwrite_ref() and simplify it
  btrfs: send: avoid unnecessary generation search at did_overwrite_ref()
  btrfs: send: directly return from will_overwrite_ref() and simplify it
  btrfs: send: avoid extra b+tree searches when checking reference overrides
  btrfs: send: remove send_progress argument from can_rmdir()
  btrfs: send: avoid duplicated orphan dir allocation and initialization
  btrfs: send: avoid unnecessary orphan dir rbtree search at can_rmdir()
  btrfs: send: reduce searches on parent root when checking if dir can be removed
  btrfs: send: iterate waiting dir move rbtree only once when processing refs
  btrfs: send: use MT_FLAGS_LOCK_EXTERN for the backref cache maple tree
  btrfs: send: initialize all the red black trees earlier
  btrfs: send: genericize the backref cache to allow it to be reused
  btrfs: adapt lru cache to allow for 64 bits keys on 32 bits systems
  btrfs: send: cache information about created directories
  btrfs: allow a generation number to be associated with lru cache entries
  btrfs: add an api to delete a specific entry from the lru cache
  btrfs: send: use the lru cache to implement the name cache
  btrfs: send: update size of roots array for backref cache entries
  btrfs: send: cache utimes operations for directories if possible

Signed-off-by: Filipe Manana <[e-mail]>
---
 fs/btrfs/send.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 20fcf1c0832a..5ac3cff7bd68 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -8140,7 +8140,7 @@  long btrfs_ioctl_send(struct inode *inode, struct btrfs_ioctl_send_args *arg)
 	INIT_LIST_HEAD(&sctx->name_cache_list);
 
 	INIT_LIST_HEAD(&sctx->backref_cache.lru_list);
-	mt_init(&sctx->backref_cache.entries);
+	mt_init_flags(&sctx->backref_cache.entries, MT_FLAGS_LOCK_EXTERN);
 
 	sctx->flags = arg->flags;