Re: [PATCH] slub: Fix calculation of cpu slabs

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

On Tue, Sep 10, 2013 at 11:43:37AM +0800, Li Zefan wrote:
>  /sys/kernel/slab/:t-0000048 # cat cpu_slabs
>  231 N0=16 N1=215
>  /sys/kernel/slab/:t-0000048 # cat slabs
>  145 N0=36 N1=109
>
>See, the number of slabs is smaller than that of cpu slabs.
>
>The bug was introduced by commit 49e2258586b423684f03c278149ab46d8f8b6700
>("slub: per cpu cache for partial pages").
>
>We should use page->pages instead of page->pobjects when calculating
>the number of cpu partial slabs. This also fixes the mapping of slabs
>and nodes.
>
>As there's no variable storing the number of total/active objects in
>cpu partial slabs, and we don't have user interfaces requiring those
>statistics, I just add WARN_ON for those cases.
>
>Cc: <stable@vger.kernel.org> # 3.2+
>Signed-off-by: Li Zefan <lizefan@huawei.com>

Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>

>---
> mm/slub.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
>diff --git a/mm/slub.c b/mm/slub.c
>index e3ba1f2..6ea461d 100644
>--- a/mm/slub.c
>+++ b/mm/slub.c
>@@ -4300,7 +4300,13 @@ static ssize_t show_slab_objects(struct kmem_cache *s,
>
> 			page = ACCESS_ONCE(c->partial);
> 			if (page) {
>-				x = page->pobjects;
>+				node = page_to_nid(page);
>+				if (flags & SO_TOTAL)
>+					WARN_ON_ONCE(1);
>+				else if (flags & SO_OBJECTS)
>+					WARN_ON_ONCE(1);
>+				else
>+					x = page->pages;
> 				total += x;
> 				nodes[node] += x;
> 			}
>-- 
>1.8.0.2
>
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