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* [PATCH] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly
@ 2019-10-25 23:27 Roman Gushchin
  2019-10-30 19:40 ` Roman Gushchin
                   ` (2 more replies)
  0 siblings, 3 replies; 5+ messages in thread
From: Roman Gushchin @ 2019-10-25 23:27 UTC (permalink / raw)
  To: linux-mm
  Cc: Michal Hocko, Johannes Weiner, linux-kernel, kernel-team,
	Roman Gushchin, Vladimir Davydov, Shakeel Butt

page_cgroup_ino() doesn't return a valid memcg pointer for non-compund
slab pages, because it depends on PgHead AND PgSlab flags to be set
to determine the memory cgroup from the kmem_cache.
It's correct for compound pages, but not for generic small pages. Those
don't have PgHead set, so it ends up returning zero.

Fix this by replacing the condition to PageSlab() && !PageTail().

Before this patch:
[root@localhost ~]# ./page-types -c /sys/fs/cgroup/user.slice/user-0.slice/user@0.service/ | grep slab
0x0000000000000080	        38        0  _______S___________________________________	slab

After this patch:
[root@localhost ~]# ./page-types -c /sys/fs/cgroup/user.slice/user-0.slice/user@0.service/ | grep slab
0x0000000000000080	       147        0  _______S___________________________________	slab

Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Shakeel Butt <shakeelb@google.com>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ea085877c548..00b4188b1bed 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -476,7 +476,7 @@ ino_t page_cgroup_ino(struct page *page)
 	unsigned long ino = 0;
 
 	rcu_read_lock();
-	if (PageHead(page) && PageSlab(page))
+	if (PageSlab(page) && !PageTail(page))
 		memcg = memcg_from_slab_page(page);
 	else
 		memcg = READ_ONCE(page->mem_cgroup);
-- 
2.17.1


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end of thread, other threads:[~2019-10-30 21:35 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2019-10-25 23:27 [PATCH] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly Roman Gushchin
2019-10-30 19:40 ` Roman Gushchin
2019-10-30 20:40 ` Shakeel Butt
2019-10-30 21:03 ` Daniel Jordan
2019-10-30 21:35   ` Roman Gushchin

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