btrfs: send: avoid unnecessary generation search at did_overwrite_ref()

At did_overwrite_ref() we always call get_inode_gen() to find out the
generation of the inode 'ow_inode'. However we don't always need to use
that generation, and in fact it's very common to not use it, so we end
up doing a b+tree search on the send root, allocating a path, etc, for
nothing. So improve on this by getting the generation only if we need
to use it.

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: 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 <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 22 insertions, 9 deletions

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index c77508b7ed68..73017be632ed 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -2193,8 +2193,8 @@ static int did_overwrite_ref(struct send_ctx *sctx,
 			    const char *name, int name_len)
 {
 	int ret;
-	u64 gen;
 	u64 ow_inode;
+	u64 ow_gen = 0;
 
 	if (!sctx->parent_root)
 		return 0;
@@ -2204,6 +2204,8 @@ static int did_overwrite_ref(struct send_ctx *sctx,
 		return ret;
 
 	if (dir != BTRFS_FIRST_FREE_OBJECTID) {
+		u64 gen;
+
 		ret = get_inode_gen(sctx->send_root, dir, &gen);
 		if (ret == -ENOENT)
 			return 0;
@@ -2224,12 +2226,15 @@ static int did_overwrite_ref(struct send_ctx *sctx,
 		return ret;
 	}
 
-	ret = get_inode_gen(sctx->send_root, ow_inode, &gen);
-	if (ret < 0)
-		return ret;
+	if (ow_inode == ino) {
+		ret = get_inode_gen(sctx->send_root, ow_inode, &ow_gen);
+		if (ret < 0)
+			return ret;
 
-	if (ow_inode == ino && gen == ino_gen)
-		return 0;
+		/* It's the same inode, so no overwrite happened. */
+		if (ow_gen == ino_gen)
+			return 0;
+	}
 
 	/*
 	 * We know that it is or will be overwritten. Check this now.
@@ -2237,11 +2242,19 @@ static int did_overwrite_ref(struct send_ctx *sctx,
 	 * inode 'ino' to be orphanized, therefore check if ow_inode matches
 	 * the current inode being processed.
 	 */
-	if ((ow_inode < sctx->send_progress) ||
-	    (ino != sctx->cur_ino && ow_inode == sctx->cur_ino &&
-	     gen == sctx->cur_inode_gen))
+	if (ow_inode < sctx->send_progress)
 		return 1;
 
+	if (ino != sctx->cur_ino && ow_inode == sctx->cur_ino) {
+		if (ow_gen == 0) {
+			ret = get_inode_gen(sctx->send_root, ow_inode, &ow_gen);
+			if (ret < 0)
+				return ret;
+		}
+		if (ow_gen == sctx->cur_inode_gen)
+			return 1;
+	}
+
 	return 0;
 }