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

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Date:	Wed, 20 Jul 2011 16:42:25 +0300 (EEST)
From:	Pekka Enberg <penberg@...nel.org>
To:	Konstantin Khlebnikov <khlebnikov@...allels.com>
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

On Wed, 20 Jul 2011, Konstantin Khlebnikov wrote:
>> 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.

I'm still surprised you are seeing failures. mm/slab.c hasn't changed 
significantly in a long time. Why hasn't anyone reported this before? I'd 
still be inclined to shift the blame to the page allocator... Mel, 
Christoph?

On Wed, 20 Jul 2011, Konstantin Khlebnikov wrote:
> 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...

So how big is 'struct kmem_cache' for your configuration anyway? Fixing 
the per-cpu data structures would be nice but I'm guessing it'll be 
slightly painful for mm/slab.c.

 			Pekka
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