Re: [PATCH] slub: do not put a slab to cpu partial list when cpu_partial is 0

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Wed, Jun 19, 2013 at 05:52:50PM +0900, Joonsoo Kim wrote:
>On Wed, Jun 19, 2013 at 04:00:32PM +0800, Wanpeng Li wrote:
>> On Wed, Jun 19, 2013 at 03:33:55PM +0900, Joonsoo Kim wrote:
>> >In free path, we don't check number of cpu_partial, so one slab can
>> >be linked in cpu partial list even if cpu_partial is 0. To prevent this,
>> >we should check number of cpu_partial in put_cpu_partial().
>> >
>> 
>> How about skip get_partial entirely? put_cpu_partial is called 
>> in two paths, one is during refill cpu partial lists in alloc 
>> slow path, the other is in free slow path. And cpu_partial is 0 
>> just in debug mode. 
>> 
>> - alloc slow path, there is unnecessary to call get_partial 
>>   since cpu partial lists won't be used in debug mode. 
>> - free slow patch, new.inuse won't be true in debug mode 
>>   which lead to put_cpu_partial won't be called.
>> 
>
>In debug mode, put_cpu_partial() can't be called already on both path.
>But, if we assign 0 to cpu_partial via sysfs, put_cpu_partial() will be called
>on free slow path. On alloc slow path, it can't be called, because following
>test in get_partial_node() is always failed.
>
>available > s->cpu_partial / 2

Is it always true? We can freeze slab from partial list, and 
s->cpu_partial is 0. 

Regards,
Wanpeng Li 

>
>Thanks.
>
>> Regards,
>> Wanpeng Li 
>> 
>> >Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>> >
>> >diff --git a/mm/slub.c b/mm/slub.c
>> >index 57707f0..7033b4f 100644
>> >--- a/mm/slub.c
>> >+++ b/mm/slub.c
>> >@@ -1955,6 +1955,9 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
>> > 	int pages;
>> > 	int pobjects;
>> >
>> >+	if (!s->cpu_partial)
>> >+		return;
>> >+
>> > 	do {
>> > 		pages = 0;
>> > 		pobjects = 0;
>> >-- 
>> >1.7.9.5
>> >
>> >--
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