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

[David Rientjes]

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@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 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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