linux-kernel - Re: [PATCH] mm-slab: allocate kmem_cache with __GFP

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Date:	Sun, 31 Jul 2011 15:41:31 +0400
From:	Konstantin Khlebnikov <khlebnikov@...allels.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Christoph Lameter <cl@...ux.com>, Mel Gorman <mgorman@...e.de>,
	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH] mm-slab: allocate kmem_cache with __GFP_REPEAT

It seems someone forgot this patch,
the second one "slab: shrink sizeof(struct kmem_cache)" already in mainline

Eric Dumazet wrote:
> Le mercredi 20 juillet 2011 à 09:52 -0500, Christoph Lameter a écrit :
>> On Wed, 20 Jul 2011, Eric Dumazet wrote:
>>
>>>> Slab's kmem_cache is configured with an array of NR_CPUS which is the
>>>> maximum nr of cpus supported. Some distros support 4096 cpus in order to
>>>> accomodate SGI machines. That array then will have the size of 4096 * 8 =
>>>> 32k
>>>
>>> We currently support a dynamic schem for the possible nodes :
>>>
>>> cache_cache.buffer_size = offsetof(struct kmem_cache, nodelists) +
>>> 	nr_node_ids * sizeof(struct kmem_list3 *);
>>>
>>> We could have a similar trick to make the real size both depends on
>>> nr_node_ids and nr_cpu_ids.
>>>
>>> (struct kmem_cache)->array would become a pointer.
>>
>> We should be making it a per cpu pointer like slub then. I looked at what
>> it would take to do so a couple of month ago but it was quite invasive.
>>
>
> Lets try this first patch, simple enough : No need to setup percpu data
> for a one time use structure...
>
> [PATCH] slab: remove one NR_CPUS dependency
>
> Reduce high order allocations in do_tune_cpucache() for some setups.
> (NR_CPUS=4096 ->  we need 64KB)
>
> Signed-off-by: Eric Dumazet<eric.dumazet@...il.com>
> CC: Pekka Enberg<penberg@...nel.org>
> CC: Christoph Lameter<cl@...ux.com>
> ---
>   mm/slab.c |    5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index d96e223..862bd12 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3933,7 +3933,7 @@ fail:
>
>   struct ccupdate_struct {
>   	struct kmem_cache *cachep;
> -	struct array_cache *new[NR_CPUS];
> +	struct array_cache *new[0];
>   };
>
>   static void do_ccupdate_local(void *info)
> @@ -3955,7 +3955,8 @@ static int do_tune_cpucache(struct kmem_cache *cachep, int limit,
>   	struct ccupdate_struct *new;
>   	int i;
>
> -	new = kzalloc(sizeof(*new), gfp);
> +	new = kzalloc(sizeof(*new) + nr_cpu_ids * sizeof(struct array_cache *),
> +		      gfp);
>   	if (!new)
>   		return -ENOMEM;
>
>
>

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