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

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 9 Jan 2014 09:13:31 +0900 Joonsoo Kim <iamjoonsoo.kim@lge.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@kernel.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!