On Wed, 30 Oct 2019, Roman Gushchin 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@xxxxxx>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
