linux-kernel - Re: [PATCH] add __GFP_ZERO to GFP_LEVEL

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Date:	Wed, 25 Jul 2007 14:06:49 +0100
From:	mel@...net.ie (Mel Gorman)
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <clameter@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Daniel Phillips <phillips@...gle.com>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] add __GFP_ZERO to GFP_LEVEL_MASK

On (24/07/07 12:25), Andrew Morton didst pronounce:
> On Tue, 24 Jul 2007 12:07:51 -0700
> Christoph Lameter <clameter@....com> wrote:
> 
> > Then there are some other flags. I am wondering why they are in
> > GFP_LEVEL_MASK?
> > 
> > __GFP_COLD	Does not make sense for slab allocators since we have
> > 		to touch the page immediately.
> > 
> > __GFP_COMP	No effect. Added by the page allocator on their own
> > 		if a higher order allocs are used for a slab.
> > 
> > __GFP_MOVABLE	The movability of a slab is determined by the
> > 		options specified at kmem_cache_create time. If this is
> > 		specified at kmalloc time then we will have some random
> > 		slabs movable and others not. 
> 
> Yes, they seem inappropriate.  Especially the first two.

And the third one is also inappropriate by the definition of GFP_LEVEL_MASK
Christoph is using. If GFP_LEVEL_MASK is to be used to filter out flags
that are unsuitable for higher allocators such as slab and vmalloc, then
they shouldn't be using __GFP_MOVABLE because they are unlikely to do the
correct thing with the pages.

When the flags were added, I was treating GFP_LEVEL_MASK as a set of
allowed flags to the allocator.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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