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, 2 insertions, 0 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a6824bd04493..24745b8f2745 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6774,6 +6774,7 @@ again:
 
 	BTRFS_I(inode)->last_trans = root->fs_info->generation;
 	BTRFS_I(inode)->last_sub_trans = BTRFS_I(inode)->root->log_transid;
+	BTRFS_I(inode)->last_log_commit = BTRFS_I(inode)->root->last_log_commit;
 
 	unlock_extent_cached(io_tree, page_start, page_end, &cached_state, GFP_NOFS);
 
@@ -7018,6 +7019,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 	ei->csum_bytes = 0;
 	ei->index_cnt = (u64)-1;
 	ei->last_unlink_trans = 0;
+	ei->last_log_commit = 0;
 
 	spin_lock_init(&ei->lock);
 	ei->outstanding_extents = 0;