netdev - Re: slub numa: Fix rare allocation from unexpected node

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Message-ID: <4C515137.707@cs.helsinki.fi>
Date:	Thu, 29 Jul 2010 13:00:23 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	linux-mm@...ck.org, jamal <hadi@...erus.ca>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: slub numa: Fix rare allocation from unexpected node

Christoph Lameter wrote:
> Subject: slub numa: Fix rare allocation from unexpected node
> 
> The network developers have seen sporadic allocations resulting in objects
> coming from unexpected NUMA nodes despite asking for objects from a
> specific node.
> 
> This is due to get_partial() calling get_any_partial() if partial
> slabs are exhausted for a node even if a node was specified and therefore
> one would expect allocations only from the specified node.
> 
> get_any_partial() sporadically may return a slab from a foreign
> node to gradually reduce the size of partial lists on remote nodes
> and thereby reduce total memory use for a slab cache.
> 
> The behavior is controlled by the remote_defrag_ratio of each cache.
> 
> Strictly speaking this is permitted behavior since __GFP_THISNODE was
> not specified for the allocation but it is certain surprising.
> 
> This patch makes sure that the remote defrag behavior only occurs
> if no node was specified.
> 
> Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>
> 
> ---
>  mm/slub.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c	2010-07-23 09:24:11.000000000 -0500
> +++ linux-2.6/mm/slub.c	2010-07-23 09:25:15.000000000 -0500
> @@ -1390,7 +1390,7 @@ static struct page *get_partial(struct k
>  	int searchnode = (node == -1) ? numa_node_id() : node;
> 
>  	page = get_partial_node(get_node(s, searchnode));
> -	if (page || (flags & __GFP_THISNODE))
> +	if (page || node != -1)
>  		return page;
> 
>  	return get_any_partial(s, flags);

Applied, thanks!
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