linux-kernel - Re: [PATCH] mm: Fix a regression where MS_SNAP_STABLE (stable pages snapshotting) was ignored

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Date:	Fri, 20 Sep 2013 09:28:07 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	Kent Overstreet <kmo@...erainc.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
	Hannes Reinecke <hare@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Fix a regression where MS_SNAP_STABLE (stable pages
 snapshotting) was ignored

On Fri, Sep 20, 2013 at 09:06:37AM +0100, Mel Gorman wrote:
> On Thu, Sep 19, 2013 at 08:06:02PM -0700, Darrick J. Wong wrote:
> > The "force" parameter in __blk_queue_bounce was being ignored, which means that
> > stable page snapshots are not always happening (on ext3).  This of course
> > leads to DIF disks reporting checksum errors, so fix this regression.
> > 
> > The regression was introduced in commit 6bc454d1 (bounce: Refactor
> > __blk_queue_bounce to not use bi_io_vec)
> > 
> > Reported-by: Mel Gorman <mgorman@...e.de>
> > Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> 
> I have no means of testing it but it looks right and thanks for checking
> DIF disks.
> 
> Acked-by: Mel Gorman <mgorman@...e.de>
> 

That said the two checks are now redundant. They could just be deleted
and depend entirely on the following check within the loop

                if (page_to_pfn(page) <= queue_bounce_pfn(q) && !force)
                        continue;

with an update to the comment explaining that the check is for pages
below the bounce pfn or for bios that require stable writes

-- 
Mel Gorman
SUSE Labs
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