linux-kernel - Re: WARNING: at mm/page_alloc.c:1159 get_page_from

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Message-ID: <alpine.LFD.2.01.0906170931520.16802@localhost.localdomain>
Date:	Wed, 17 Jun 2009 09:39:43 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Catalin Marinas <catalin.marinas@....com>,
	fengguang.wu@...el.com, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org
Subject: Re: WARNING: at mm/page_alloc.c:1159
 get_page_from_freelist+0x325/0x655()

On Wed, 17 Jun 2009, Ingo Molnar wrote:
> 
> a new warning started popping up today, in the new page allocator 
> code. The allocation came from kmemleak:

We should probably print out the order.

Right now it warns about any order but 0, and I think that's likely bogus. 
It's fine to allow small orders (I'd suggest 0-2), since we should always 
be able to get those, and small kmalloc's generally do want more than one 
page just to avoid crazy fragmentation issues.

See, for example, the whole 'slab_break_gfp_order' logic in mm/slab.c: it 
very much expects to be able to use order-1 allocations for kmalloc() if 
there is enough memory (where "enough" is actually just 32MB). And slub 
seems to put some limit at PAGE_ALLOC_COSTLY_ORDER (3).

So apart from anything else (ie this particular case is possibly fixable 
in kmemleak), I do think that we should likely allow at least order-1 and 
possible order-2 allocations with __GFP_NOFAIL too.

		Linus
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