linux-kernel - [PATCH 3.2 014/200] slub: Fix calculation of cpu slabs

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Message-ID: <lsq.1396221815.223795276@decadent.org.uk>
Date:	Mon, 31 Mar 2014 00:23:35 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Li Zefan" <lizefan@...wei.com>,
	"Wanpeng Li" <liwanp@...ux.vnet.ibm.com>,
	"Pekka Enberg" <penberg@...nel.org>,
	"Christoph Lameter" <cl@...ux.com>
Subject: [PATCH 3.2 014/200] slub: Fix calculation of cpu slabs

3.2.56-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Li Zefan <lizefan@...wei.com>

commit 8afb1474db4701d1ab80cd8251137a3260e6913e upstream.

  /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.

Acked-by: Christoph Lameter <cl@...ux.com>
Reviewed-by: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Signed-off-by: Li Zefan <lizefan@...wei.com>
Signed-off-by: Pekka Enberg <penberg@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/slub.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4483,7 +4483,13 @@ static ssize_t show_slab_objects(struct
 			page = 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;
 			}

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