linux-kernel - Re: [PATCH] fix crash when using XFS on loopback

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Date:	Wed, 8 Jan 2014 16:19:36 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Pekka Enberg <penberg@...nel.org>, Helge Deller <deller@....de>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Christoph Lameter <cl@...ux.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-parisc@...r.kernel.org
Subject: Re: [PATCH] fix crash when using XFS on loopback

On Thu, 9 Jan 2014 09:13:31 +0900 Joonsoo Kim <iamjoonsoo.kim@....com> wrote:

> On Wed, Jan 08, 2014 at 01:59:30PM -0800, Andrew Morton wrote:
> > On Wed, 8 Jan 2014 23:37:49 +0200 Pekka Enberg <penberg@...nel.org> wrote:
> > 
> > > The patch looks good to me but it probably should go through Andrew's tree.
> > 
> > yup.
> > 
> > page_mapping() will be called quite frequently, and adding a new
> > test-n-branch in there will be somewhat costly.  We might end up with a
> > better kernel if we were to instead revert 8456a648cf44f.  How useful
> > was that patch?
> 
> Hello,
> 
> Performance effect of this patch was decribed in the cover-letter, but
> I missed to attach it to patch description. Sorry about that.
> 
> In summary, this patch saves some memory and decreases cache-footprint
> so that it increases performance.
> 
> Here goes the description in cover-letter.
> 
> ...
>
> cache-misses are reduced by this patchset, roughly 5%.
> And elapsed times are also improved by 3.1% to baseline.

ah, OK, thanks, useful.  A few instructions added to page_mapping()
won't have effects like that!
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