Btrfs: fix a bug in checking whether a inode is already in log

This is based on Josef's "Btrfs: turbo charge fsync".

The current btrfs checks if an inode is in log by comparing
root's last_log_commit to inode's last_sub_trans[2].

But the problem is that this root->last_log_commit is shared among
inodes.

Say we have N inodes to be logged, after the first inode,
root's last_log_commit is updated and the N-1 remained files will
be skipped.

This fixes the bug by keeping a local copy of root's last_log_commit
inside each inode and this local copy will be maintained itself.

[1]: we regard each log transaction as a subset of btrfs's transaction,
i.e. sub_trans

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 7c7bf818f3c1..ed8ca7ca5eff 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -144,6 +144,9 @@ struct btrfs_inode {
 	/* flags field from the on disk inode */
 	u32 flags;
 
+	/* a local copy of root's last_log_commit */
+	unsigned long last_log_commit;
+
 	/*
 	 * Counters to keep track of the number of extent item's we may use due
 	 * to delalloc and such.  outstanding_extents is the number of extent
@@ -203,15 +206,10 @@ static inline bool btrfs_is_free_space_inode(struct inode *inode)
 
 static inline int btrfs_inode_in_log(struct inode *inode, u64 generation)
 {
-	struct btrfs_root *root = BTRFS_I(inode)->root;
-	int ret = 0;
-
-	mutex_lock(&root->log_mutex);
 	if (BTRFS_I(inode)->logged_trans == generation &&
-	    BTRFS_I(inode)->last_sub_trans <= root->last_log_commit)
-		ret = 1;
-	mutex_unlock(&root->log_mutex);
-	return ret;
+	    BTRFS_I(inode)->last_sub_trans <= BTRFS_I(inode)->last_log_commit)
+		return 1;
+	return 0;
 }
 
 #endif