linux-kernel - Re: [patch 4/6] SLUB: Avoid touching page struct when freeing to per cpu slab

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Date:	Thu, 23 Aug 2007 17:05:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <clameter@....com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 4/6] SLUB: Avoid touching page struct when freeing to
	per cpu slab

On Wed, 2007-08-22 at 23:46 -0700, Christoph Lameter wrote:
> plain text document attachment
> (0008-SLUB-Avoid-touching-page-struct-when-freeing-to-per.patch)
> Set c->node to -1 if we allocate from a debug slab instead for SlabDebug
> which requires access the page struct cacheline.

this relies on node_match() which will only ever return !1 when
CONFIG_NUMA

> Signed-off-by: Christoph Lameter <clameter@....com>
> ---
>  mm/slub.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> Index: linux-2.6.23-rc3-mm1/mm/slub.c
> ===================================================================
> --- linux-2.6.23-rc3-mm1.orig/mm/slub.c	2007-08-22 17:20:28.000000000 -0700
> +++ linux-2.6.23-rc3-mm1/mm/slub.c	2007-08-22 17:20:33.000000000 -0700
> @@ -1517,6 +1517,7 @@ debug:
>  
>  	c->page->inuse++;
>  	c->page->freelist = object[c->offset];
> +	c->node = -1;
>  	slab_unlock(c->page);
>  	return object;
>  }
> @@ -1540,8 +1541,7 @@ static void __always_inline *slab_alloc(
>  
>  	local_irq_save(flags);
>  	c = get_cpu_slab(s, smp_processor_id());
> -	if (unlikely(!c->page || !c->freelist ||
> -					!node_match(c, node)))
> +	if (unlikely(!c->freelist || !node_match(c, node)))
>  
>  		object = __slab_alloc(s, gfpflags, node, addr, c);
>  
> @@ -1650,7 +1650,7 @@ static void __always_inline slab_free(st
>  	local_irq_save(flags);
>  	debug_check_no_locks_freed(object, s->objsize);
>  	c = get_cpu_slab(s, smp_processor_id());
> -	if (likely(page == c->page && !SlabDebug(page))) {
> +	if (likely(page == c->page && c->node >= 0)) {
>  		object[c->offset] = c->freelist;
>  		c->freelist = object;
>  	} else
> 

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