linux-kernel - Re: [PATCH 01/16] slab: correct pfmemalloc check

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Message-ID: <20130912065138.GA8055@lge.com>
Date:	Thu, 12 Sep 2013 15:51:38 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH 01/16] slab: correct pfmemalloc check

On Wed, Sep 11, 2013 at 02:30:03PM +0000, Christoph Lameter wrote:
> On Thu, 22 Aug 2013, Joonsoo Kim wrote:
> 
> > And, therefore we should check pfmemalloc in page flag of first page,
> > but current implementation don't do that. virt_to_head_page(obj) just
> > return 'struct page' of that object, not one of first page, since the SLAB
> > don't use __GFP_COMP when CONFIG_MMU. To get 'struct page' of first page,
> > we first get a slab and try to get it via virt_to_head_page(slab->s_mem).
> 
> Maybe using __GFP_COMP would make it consistent across all allocators and
> avoid the issue? We then do only have to set the flags on the first page.

Yes, you are right. It can be solved by using __GFP_COMP.
But I made this patch to clarify the problem in current code and to
be merged seperately.

If I solve the problem with __GFP_COMP which is implemented in [09/16]
of this patchset, it would also weaken the purpose of that patch.

Thanks.
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