linux-kernel - Re: [PATCH v1 0/9] do not use s

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Date:	Thu, 22 Mar 2012 14:42:53 +0100
From:	Jan Kara <jack@...e.cz>
To:	Artem Bityutskiy <dedekind1@...il.com>
Cc:	Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
	Ext4 Mailing List <linux-ext4@...r.kernel.org>,
	Linux FS Maling List <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Maling List <linux-kernel@...r.kernel.org>
Subject: 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:
> > > 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.
> 
> >   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@...ck:~/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 <jack@...e.cz>
SUSE Labs, CR
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