linux-kernel - Re: [PATCH v3 3/3] mm: Wait for writeback when grabbing pages to begin a write

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Date:	Wed, 4 May 2011 14:48:03 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Theodore Ts'o <tytso@....edu>,
	Christoph Hellwig <hch@...radead.org>,
	Chris Mason <chris.mason@...cle.com>,
	Jeff Layton <jlayton@...hat.com>, Jan Kara <jack@...e.cz>,
	Dave Chinner <david@...morbit.com>,
	Joel Becker <jlbec@...lplan.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jens Axboe <axboe@...nel.dk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Mingming Cao <mcao@...ibm.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] mm: Wait for writeback when grabbing pages to
 begin a write

On Wed, May 04, 2011 at 10:42:27AM -0700, Darrick J. Wong wrote:
> When grabbing a page for a buffered IO write, the mm should wait for writeback
> on the page to complete so that the page does not become writable during the IO
> operation.
> 
> Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
> ---
> 
>  mm/filemap.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index c641edf..c22675f 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2287,8 +2287,10 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
>  		gfp_notmask = __GFP_FS;
>  repeat:
>  	page = find_lock_page(mapping, index);
> -	if (page)
> +	if (page) {
> +		wait_on_page_writeback(page);
>  		return page;
> +	}

		goto found;

>  
>  	page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~gfp_notmask);
>  	if (!page)
> @@ -2301,6 +2303,7 @@ repeat:
>  			goto repeat;
>  		return NULL;
>  	}

found:
> +	wait_on_page_writeback(page);
>  	return page;
>  }
>  EXPORT_SYMBOL(grab_cache_page_write_begin);
--
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