linux-kernel - Re: [patch 12/23] SLUB: Trigger defragmentation from memory reclaim

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Message-ID: <Pine.LNX.4.64.0711071032460.9857@schroedinger.engr.sgi.com>
Date:	Wed, 7 Nov 2007 10:34:42 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Johannes Weiner <hannes-kernel@...urebad.de>
cc:	akpm@...ux-foundatin.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Mel Gorman <mel@...net.ie>
Subject: Re: [patch 12/23] SLUB: Trigger defragmentation from memory reclaim

On Wed, 7 Nov 2007, Johannes Weiner wrote:

> > @@ -210,6 +218,8 @@ unsigned long shrink_slab(unsigned long
> >                 shrinker->nr += total_scan;
> >         }
> >         up_read(&shrinker_rwsem);
> > +       if (gfp_mask & __GFP_FS)
> > +               kmem_cache_defrag(zone ? zone_to_nid(zone) : -1);
> >         return ret;
> >  }
> 
> What about the objects that kmem_cache_defrag() releases?  Shouldn't
> they be counted too?
> 
>      ret += kmem_cache_defrag(...)
> 
> Or am I overseeing something here?

kmem_cache_defrag returns the number of pages that were released by defrag 
actions.

shrink_slab returns the number of objects released by the shrinkers. 
kmem_cache_defrag has no way of knowing how many objects where released by 
the kick methods. The kick method may have chosen to reallocate the 
object.


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