Messages in this thread | | | From | Naoya Horiguchi <> | Subject | Re: [PATCH v2] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly | Date | Thu, 31 Oct 2019 09:38:40 +0000 |
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On Wed, Oct 30, 2019 at 09:16:08PM -0700, Andrew Morton wrote: > 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?
hwpoison_filter_task() uses output of page_cgroup_ino() in order to filter error injection events based on memcg. So if page_cgroup_ino() fails to return memcg pointer, we just fail to inject memory error. Considering that hwpoison filter is for testing, affected users are limited and the impact should be marginal.
> > IOW, should we backport this into -stable?
I think yes, because the patch is small enough and clearly fixes a bug.
Thanks, Naoya Horiguchi
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