linux-ext4 - Re: [PATCH 2/5] ext4: Use redirty_page_for_writepage() in ext4_bio_write

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Message-ID: <20130117212415.GD23984@quack.suse.cz>
Date:	Thu, 17 Jan 2013 22:24:15 +0100
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/5] ext4: Use redirty_page_for_writepage() in
 ext4_bio_write_page()

On Thu 17-01-13 13:35:01, Ted Tso wrote:
> On Wed, Jan 02, 2013 at 06:45:41PM +0100, Jan Kara wrote:
> > When we cannot write a page we should use redirty_page_for_writepage()
> > instead of plain set_page_dirty(). That tells writeback code we have
> > problems, redirties only the page (redirtying buffers is not needed),
> > and updates mm accounting of failed page writes.
> > 
> > Also move clearing of buffer dirty flag after io_submit_add_bh(). At that
> > moment we are sure buffer will be going to disk.
> > 
> > Signed-off-by: Jan Kara <jack@...e.cz>
> 
> This sounds like a bug fix, not just a clean up.  Do you think the
  Yes, it's a bug fix.

> impact of not using redirty_page_for_writeback() is bad enough that we
> should add a cc: stable@...r.kernel.org tag?  As I recall, not doing
> this would end up leaving the page flags and radix tree to be
> inconsistent, right?
  No, it shouldn't cause any such serious harm. Just writeback may retry
writing the inode immediately (it backs off if it sees skipped pages) which
could result in needless spinning. Also some mm/bdi statistics will get
slightly off. But all in all I don't think it's a stable material.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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