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>

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index c77508b..73017be 100644 (file)
--- 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;
 }