linux-kernel - Re: possible regression on 3.13 when calling flush_dcache

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Message-ID: <20131220080851.GC16592@ldesroches-Latitude-E6320>
Date:	Fri, 20 Dec 2013 09:08:51 +0100
From:	Ludovic Desroches <ludovic.desroches@...el.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<linux-mmc@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Ludovic Desroches <ludovic.desroches@...el.com>
Subject: Re: possible regression on 3.13 when calling flush_dcache_page

Hello,

On Wed, Dec 18, 2013 at 04:21:17PM +0900, Joonsoo Kim wrote:
> On Mon, Dec 16, 2013 at 03:43:43PM +0100, Ludovic Desroches wrote:
> > Hello,
> > 
> > On Fri, Dec 13, 2013 at 10:59:09AM +0900, Joonsoo Kim wrote:
> > > On Thu, Dec 12, 2013 at 03:36:19PM +0100, Ludovic Desroches wrote:
> > > > fix mmc mailing list address error
> > > > 
> > > > On Thu, Dec 12, 2013 at 03:31:50PM +0100, Ludovic Desroches wrote:
> > > > > Hi,
> > > > > 
> > > > > With v3.13-rc3 I have an error when the atmel-mci driver calls
> > > > > flush_dcache_page (log at the end of the message).
> > > > > 
> > > > > Since I didn't have it before, I did a git bisect and the commit introducing
> > > > > the error is the following one:
> > > > > 
> > > > > 106a74e slab: replace free and inuse in struct slab with newly introduced active
> > > > > 
> > > > > I don't know if this commit has introduced a bug or if it has revealed a bug
> > > > > in the atmel-mci driver.
> > > 
> > > Hello,
> > > 
> > > I think that this commit may not introduce a bug. This patch remove one
> > > variable on slab management structure and replace variable name. So there
> > > is no functional change.
> > > 
> > 
> > If I have reverted this patch and other ones you did on top of it and
> > the issue disappear.
> 
> Hello,
> 
> Could you give me your '/proc/slabinfo' before/after this commit (106a74e)?
> 
> And how about testing with artificially increasing size of struct slab on
> top of this commit (106a74e)?
> 
> I really wonder why the problem happens, because this doesn't cause any
> functional change as far as I know. Only side-effect from this patch is
> decreasing size of struct slab.

Sorry I am not at the office, I have tried to reproduce it with a
different device and a different sdcard but without success. I'll test
it on Monday.

Regards

Ludovic

> 
> Thanks.
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index 2ec2336..d2240fd 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -174,6 +174,7 @@ struct slab {
>         struct {
>                 struct list_head list;
>                 void *s_mem;            /* including colour offset */
> +               unsigned int x;
>                 unsigned int active;    /* num of objs active in slab */
>         };
>  };
> 
> > 
> > > I doubt that side-effect of this patch reveals a bug in other place.
> > > Side-effect is reduced memory usage for slab management structure. It would
> > > makes some slabs have more objects with more density since slab management
> > > structure is sometimes on the page for objects. So if it diminishes, more
> > > objects can be in the page.
> > > 
> > > Anyway, I will look at it more. If you have any progress, please let me know.
> > 
> > No progress at the moment.
> 
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