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

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Date:	Wed, 20 Jul 2011 17:28:10 +0400
From:	Konstantin Khlebnikov <khlebnikov@...allels.com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matt Mackall <mpm@...enic.com>,
	"mgorman@...e.de" <mgorman@...e.de>
Subject: Re: [PATCH] mm-slab: allocate kmem_cache with __GFP_REPEAT

Pekka Enberg wrote:
> On Wed, 20 Jul 2011, Konstantin Khlebnikov wrote:
>> Order of sizeof(struct kmem_cache) can be bigger than PAGE_ALLOC_COSTLY_ORDER,
>> thus there is a good chance of unsuccessful allocation.
>> With __GFP_REPEAT buddy-allocator will reclaim/compact memory more aggressively.
>>
>> Signed-off-by: Konstantin Khlebnikov<khlebnikov@...nvz.org>
>> ---
>> mm/slab.c |    2 +-
>> 1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/slab.c b/mm/slab.c
>> index d96e223..53bddc8 100644
>> --- a/mm/slab.c
>> +++ b/mm/slab.c
>> @@ -2304,7 +2304,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
>> 		gfp = GFP_NOWAIT;
>>
>> 	/* Get cache's description obj. */
>> -	cachep = kmem_cache_zalloc(&cache_cache, gfp);
>> +	cachep = kmem_cache_zalloc(&cache_cache, gfp | __GFP_REPEAT);
>> 	if (!cachep)
>> 		goto oops;
>
> The changelog isn't that convincing, really. This is kmem_cache_create()
> so I'm surprised we'd ever get NULL here in practice. Does this fix some
> problem you're seeing? If this is really an issue, I'd blame the page
> allocator as GFP_KERNEL should just work.

nf_conntrack creates separate slab-cache for each net-namespace,
this patch of course not eliminates the chance of failure, but makes it more acceptable.

struct kmem_size for slub is more compact, it uses pecpu-pointers instead of dumb NR_CPUS-size array.
probably better to fix this side...

>
>   			Pekka

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