RE: [f2fs-dev] [PATCH] f2fs: fix dirty page accounting when redirty

[Chao Yu <chao2.yu@samsung.com>]

Hi,

> -----Original Message-----
> From: Dave Chinner [mailto:david@fromorbit.com]
> Sent: Saturday, March 01, 2014 8:27 AM
> To: Chao Yu
> Cc: ???; linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org;
> linux-f2fs-devel@lists.sourceforge.net
> Subject: Re: [f2fs-dev] [PATCH] f2fs: fix dirty page accounting when redirty
> 
> On Fri, Feb 28, 2014 at 10:12:05AM +0800, Chao Yu wrote:
> > We should de-account dirty counters for page when redirty in ->writepage().
> >
> > Wu Fengguang described in 'commit 971767caf632190f77a40b4011c19948232eed75':
> > "writeback: fix dirtied pages accounting on redirty
> > De-account the accumulative dirty counters on page redirty.
> >
> > Page redirties (very common in ext4) will introduce mismatch between
> > counters (a) and (b)
> >
> > a) NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied
> > b) NR_WRITTEN, BDI_WRITTEN
> >
> > This will introduce systematic errors in balanced_rate and result in
> > dirty page position errors (ie. the dirty pages are no longer balanced
> > around the global/bdi setpoints)."
> >
> > Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> > ---
> >  fs/f2fs/checkpoint.c |    1 +
> >  fs/f2fs/data.c       |    1 +
> >  fs/f2fs/node.c       |    1 +
> >  3 files changed, 3 insertions(+)
> >
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index c8516ee..f069249 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -178,6 +178,7 @@ no_write:
> >  redirty_out:
> >  	dec_page_count(sbi, F2FS_DIRTY_META);
> >  	wbc->pages_skipped++;
> > +	account_page_redirty(page);
> >  	set_page_dirty(page);
> >  	return AOP_WRITEPAGE_ACTIVATE;
> 
> redirty_page_for_writepage()?

set_page_dirty() in a_ops of f2fs not only call __set_page_dirty_nobuffers(),
but also set some private data of page and print trace info.
So it seems we could not easily replace with redirty_page_for_writepage().

Thanks.

> 
> Cheers,
> 
> Dave.
> --
> Dave Chinner
> david@fromorbit.com