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

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Date:	Mon, 23 Jul 2007 15:50:07 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	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_ZERP to GFP_LEVEL_MASK

On Mon, 23 Jul 2007, Andrew Morton wrote:

> On Mon, 23 Jul 2007 14:43:23 -0700
> Christoph Lameter <clameter@....com> wrote:
> 
> > __GFP_ZERO is implemented by the slab allocators (the page allocator
> > has no knowledge about the length of the object to be zeroed). The slab
> > allocators do not pass __GFP_ZERO to the page allocator.
> 
> OK, well that was weird.  So
> 
> 	kmalloc(42, GFP_KERNEL|__GFP_ZERO);
> 
> duplicates
> 
> 	kzalloc(42, GFP_KERNEL);

Correct.

> Why do it both ways?

There are now ~2.5k uses of kzalloc in the kernel.

kzalloc and friends implies that we need to duplicate all allocator 
functions. That was never done for NUMA allocators there was never a 
kzalloc_node f.e..

kzalloc also cannot be used in a parameterized way in a derived allocator 
where you would simply pass on the gfp flags.

__GFP_ZERO support allows all allocators to work in a consistent way. 
There is no need to special case slab zeroing allocation.

kzalloc could be removed.

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