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

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Date:	Wed, 22 Apr 2009 13:11:44 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Mel Gorman <mel@....ul.ie>, Pekka Enberg <penberg@...helsinki.fi>
cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 02/22] Do not sanity check order in the fast path

On Wed, 22 Apr 2009, Mel Gorman wrote:

> If there are users with good reasons, then we could convert this to WARN_ON
> to fix up the callers. I suspect that the allocator can already cope with
> recieving a stupid order silently but slowly. It should go all the way to the
> bottom and just never find anything useful and return NULL.  zone_watermark_ok
> is the most dangerous looking part but even it should never get to MAX_ORDER
> because it should always find there are not enough free pages and return
> before it overruns.
> 

slub: enforce MAX_ORDER

slub_max_order may not be equal to or greater than MAX_ORDER.

Additionally, if a single object cannot be placed in a slab of
slub_max_order, it still must allocate slabs below MAX_ORDER.

Cc: Christoph Lameter <cl@...ux-foundation.org>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 mm/slub.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1909,7 +1909,7 @@ static inline int calculate_order(int size)
 	 * Doh this slab cannot be placed using slub_max_order.
 	 */
 	order = slab_order(size, 1, MAX_ORDER, 1);
-	if (order <= MAX_ORDER)
+	if (order < MAX_ORDER)
 		return order;
 	return -ENOSYS;
 }
@@ -2522,6 +2522,7 @@ __setup("slub_min_order=", setup_slub_min_order);
 static int __init setup_slub_max_order(char *str)
 {
 	get_option(&str, &slub_max_order);
+	slub_max_order = min(slub_max_order, MAX_ORDER - 1);
 
 	return 1;
 }
--
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