linux-kernel - Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache

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Message-Id: <1228939070.3726.134.camel@calx>
Date:	Wed, 10 Dec 2008 13:57:50 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] Do not pass the SLAB flags as GFP in slob
	kmem_cache_create

On Wed, 2008-12-10 at 22:34 +0300, Cyrill Gorcunov wrote:
> [Catalin Marinas - Wed, Dec 10, 2008 at 05:36:33PM +0000]
> | It looks like the kmem_cache_create() function in the slob allocator
> | passes the SLAB flags as GFP flags to the slob_alloc() function. The
> | patch changes this call to pass GFP_KERNEL as the other allocators seem
> | to do.
> | 
> | Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> | Cc: Matt Mackall <mpm@...enic.com>
> | ---
> |  mm/slob.c |    2 +-
> |  1 files changed, 1 insertions(+), 1 deletions(-)
> | 
> | diff --git a/mm/slob.c b/mm/slob.c
> | index ff5a98d..dce9258 100644
> | --- a/mm/slob.c
> | +++ b/mm/slob.c
> | @@ -538,7 +538,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
> |  	struct kmem_cache *c;
> |  
> |  	c = slob_alloc(sizeof(struct kmem_cache),
> | -		flags, ARCH_KMALLOC_MINALIGN, -1);
> | +		GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
> |  
> |  	if (c) {
> |  		c->name = name;
> |
> 
> Hi Catalin,
> 
> this would make the following line in slob_alloc
> 
> 	...
> 	if (unlikely((gfp & __GFP_ZERO) && b))
> 		memset(b, 0, size);
>  	...
> 
> useless. Not sure if it will be good :)

I think that's fine. Notice that this is not the allocation of an
object, but the allocation of a cache descriptor. We save the flags
inside the descriptor so that when the user calls kmem_cache_alloc, we
can pass them along to slob_alloc, where GFP_ZERO can take effect.

So, if we're comfortable with the idea that we can only create caches in
'normal' contexts, then I think the patch is fine.

-- 
Mathematics is the supreme nostalgia of our time.

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