Re: [PATCH] mm-slab: allocate kmem_cache with __GFP_REPEAT

Konstantin Khlebnikov
2011-07-31T11:41:40Z

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@gmail.com>
> CC: Pekka Enberg<penberg@kernel.org>
> CC: Christoph Lameter<cl@linux.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;