linux-kernel - Re: [PATCH] mm: mark page accessed before we write

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Date:	Thu, 2 Jul 2009 15:46:08 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Josef Bacik <josef@...hat.com>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: mark page accessed before we write_end

On Thu, Jul 02, 2009 at 09:05:00AM -0400, Josef Bacik wrote:
> Hello,
> 
> In testing a backport of the write_begin/write_end AOPs, a 10% re-read
> regression was noticed when running iozone.  This regression was introduced
> because the old AOPs would always do a mark_page_accessed(page) after the
> commit_write, but when the new AOPs where introduced, the only place this was
> kept was in pagecache_write_end().  This patch does the same thing in the
> generic case as what is done in pagecache_write_end(), which is just to mark
> the page accessed before we do write_end().  Thank you,
> 
> Signed-off-by: Josef Bacik <jbacik@...hat.com>

Nasty bug. I'm sure (without looking at history) it's my fault :(
Good catch, thanks.

Acked-by: Nick Piggin <npiggin@...e.de>

> ---
>  mm/filemap.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 2239671..ccea3b6 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2272,6 +2272,7 @@ again:
>  		pagefault_enable();
>  		flush_dcache_page(page);
>  
> +		mark_page_accessed(page);
>  		status = a_ops->write_end(file, mapping, pos, bytes, copied,
>  						page, fsdata);
>  		if (unlikely(status < 0))
> -- 
> 1.5.4.3
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