linux-kernel - Re: [PATCH 02/22] Do not sanity check order in the fast path

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Date:	Fri, 24 Apr 2009 07:16:59 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 02/22] Do not sanity check order in the fast path

On Fri, 2009-04-24 at 11:34 +0100, Mel Gorman wrote:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1464aca..1c60141 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1434,7 +1434,6 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
>  	int did_zlc_setup = 0;		/* just call zlc_setup() one time */
> 
>  	classzone_idx = zone_idx(preferred_zone);
> -	VM_BUG_ON(order >= MAX_ORDER);
> 
>  zonelist_scan:
>  	/*
> @@ -1692,6 +1691,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	struct task_struct *p = current;
> 
>  	/*
> +	 * In the slowpath, we sanity check order to avoid ever trying to
> +	 * reclaim >= MAX_ORDER areas which will never succeed. Callers may
> +	 * be using allocators in order of preference for an area that is
> +	 * too large. 
> +	 */
> +	if (WARN_ON_ONCE(order >= MAX_ORDER))
> +		return NULL;
> +
> +	/*
>  	 * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and
>  	 * __GFP_NOWARN set) should not cause reclaim since the subsystem
>  	 * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim



Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>

-- Dave

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