Re: [PATCH v1 0/9] do not use s_dirt in ext4

On Thu 22-03-12 13:25:37, Artem Bityutskiy wrote:

On Thu, 2012-03-22 at 11:33 +0100, Jan Kara wrote:

quoted

quoted

However, if there is _no_ journal, the 'write_super' is initialized, and
in many places the 's_dirt' flag is set, and thus VFS services seem to
be actively used.

  Which many places are you speaking about? Grep shows 4 places with
sb->s_dirt = 1;

Well, with 'ext4_mark_super_dirty()' there are still 6 or something
places.

quoted

  You remove two of those in your cleanups so only
__ext4_handle_dirty_super() remains. That is called from 3 (4 after your
cleanups) places and they happen so rarely (during filesystem resize or
when we start using some feature on the filesystem) that if you use
sync_buffer() from all of them, it should be fine.

But AFAIKC, the whole '__ext4_handle_dirty_super()' also falls-back to
marking the superblock as dirty if the file-system has no journal for
some reasons, right?

  Yes. And I wrote that if you do sync_buffer(EXT4_SB(sb)->s_sbh) instead
of marking superblock dirty, it would be fine.

But I do not really understand what
'ext4_handle_valid()' does. If I grep for 'ext4_handle_dirty_super()' -
there are many places places where it is used, and a few are obviously
for the superblocks.

  ext4_handle_valid() is false if and only if ext4 is in no-journal mode.
If I grep for ext4_handle_dirty_super() I see:
jack@quack:~/source/linux-fs/fs/ext4> grep "ext4_handle_dirty_super" *.c
ext4_jbd2.c:int __ext4_handle_dirty_super(const char *where, unsigned int line,
resize.c:	err = ext4_handle_dirty_super(handle, sb);
resize.c:	ext4_handle_dirty_super(handle, sb);
xattr.c:		ext4_handle_dirty_super(handle, sb);

  So not really many cases...
								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR