From: Andrew Morton <akpm@linux-foundation.org>
To: Roman Gushchin <guro@fb.com>
Cc: <linux-mm@kvack.org>, Michal Hocko <mhocko@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
<linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH v2] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly
Date: Wed, 30 Oct 2019 21:16:08 -0700 [thread overview]
Message-ID: <20191030211608.29f8fc92e07fd2ac2ef4d1d3@linux-foundation.org> (raw)
In-Reply-To: <20191031012151.2722280-1-guro@fb.com>
On Wed, 30 Oct 2019 18:21:51 -0700 Roman Gushchin <guro@fb.com> wrote:
> page_cgroup_ino() doesn't return a valid memcg pointer for non-compound
> 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>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Affects /proc/kpagecgroup, but page_cgroup_ino() is also used in the
memory-failure code - I wonder what effect this bug has there?
IOW, should we backport this into -stable?
next prev parent reply other threads:[~2019-10-31 4:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-31 1:21 [PATCH v2] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly Roman Gushchin
2019-10-31 4:16 ` Andrew Morton [this message]
2019-10-31 9:38 ` Naoya Horiguchi
2019-10-31 15:49 ` Roman Gushchin
2019-10-31 18:16 ` David Rientjes
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