btrfs: avoid unnecessarily logging directories that had no changes

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There are several cases where when logging an inode we need to log its
parent directories or logging subdirectories when logging a directory.

There are cases however where we end up logging a directory even if it was
not changed in the current transaction, no dentries added or removed since
the last transaction. While this is harmless from a functional point of
view, it is a waste time as it brings no advantage.

One example where this is triggered is the following:

  $ mkfs.btrfs -f /dev/sdc
  $ mount /dev/sdc /mnt

  $ mkdir /mnt/A
  $ mkdir /mnt/B
  $ mkdir /mnt/C

  $ touch /mnt/A/foo
  $ ln /mnt/A/foo /mnt/B/bar
  $ ln /mnt/A/foo /mnt/C/baz

  $ sync

  $ rm -f /mnt/A/foo
  $ xfs_io -c "fsync" /mnt/B/bar

This last fsync ends up logging directories A, B and C, however we only
need to log directory A, as B and C were not changed since the last
transaction commit.

So fix this by changing need_log_inode(), to return false in case the
given inode is a directory and has a ->last_trans value smaller than the
current transaction's ID.

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

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This commit is contained in:

Filipe Manana 2021-07-29 18:52:46 +01:00 • committed by David Sterba

parent 5b9b26f5d0

commit 8be2ba2e0e

1 changed files with 7 additions and 0 deletions

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fs/btrfs/tree-log.c

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