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

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Date:	Wed, 7 Nov 2007 10:28:22 +0100
From:	Johannes Weiner <hannes-kernel@...urebad.de>
To:	Christoph Lameter <clameter@....com>
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

Hi Christoph,

On Tue, Nov 06, 2007 at 05:11:42PM -0800, Christoph Lameter wrote:
> Index: linux-2.6/include/linux/slab.h
> ===================================================================
> --- linux-2.6.orig/include/linux/slab.h	2007-11-06 12:37:51.000000000 -0800
> +++ linux-2.6/include/linux/slab.h	2007-11-06 12:53:40.000000000 -0800
> @@ -63,6 +63,7 @@ void kmem_cache_free(struct kmem_cache *
>  unsigned int kmem_cache_size(struct kmem_cache *);
>  const char *kmem_cache_name(struct kmem_cache *);
>  int kmem_ptr_validate(struct kmem_cache *cachep, const void *ptr);
> +int kmem_cache_defrag(int node);

The definition in slab.c always returns 0.  Wouldn't a static inline
function in the header be better?


>   * Returns the number of slab objects which we shrunk.
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>   */
>  unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
> -                       unsigned long lru_pages)
> +                       unsigned long lru_pages, struct zone *zone)
>  {
>         struct shrinker *shrinker;
>         unsigned long ret = 0;
> @@ -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?

	Hannes
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