2019-10-25 23:29:30

by Roman Gushchin

Subject: [PATCH] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly

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/[email protected]/ | grep slab
0x0000000000000080 38 0 _______S___________________________________ slab

After this patch:
[root@localhost ~]# ./page-types -c /sys/fs/cgroup/user.slice/user-0.slice/[email protected]/ | 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 <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Shakeel Butt <[email protected]>
---
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

2019-10-30 19:46:57

by Roman Gushchin

Subject: Re: [PATCH] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly

On Fri, Oct 25, 2019 at 04:27:10PM -0700, Roman Gushchin wrote:
> 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/[email protected]/ | grep slab
> 0x0000000000000080 38 0 _______S___________________________________ slab
>
> After this patch:
> [root@localhost ~]# ./page-types -c /sys/fs/cgroup/user.slice/user-0.slice/[email protected]/ | 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 <[email protected]>
> Cc: Vladimir Davydov <[email protected]>
> Cc: Shakeel Butt <[email protected]>

Ping?

> ---
> 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
>

2019-10-30 21:08:44

by Daniel Jordan

Subject: Re: [PATCH] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly

Hi Roman,

On Fri, Oct 25, 2019 at 04:27:10PM -0700, Roman Gushchin wrote:
> 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().

You may also want to update the comment above memcg_from_slab_page():

* So this function assumes that the page can pass PageHead() and PageSlab()
* checks.

2019-10-30 21:37:05

by Roman Gushchin

Subject: Re: [PATCH] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly

On Wed, Oct 30, 2019 at 05:03:14PM -0400, Daniel Jordan wrote:
> Hi Roman,
>
> On Fri, Oct 25, 2019 at 04:27:10PM -0700, Roman Gushchin wrote:
> > 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().
>
> You may also want to update the comment above memcg_from_slab_page():
>
> * So this function assumes that the page can pass PageHead() and PageSlab()
> * checks.

Good catch, thank you! Will send v2 in no time.

2019-10-30 23:18:10

by Shakeel Butt

Subject: Re: [PATCH] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly

On Fri, Oct 25, 2019 at 4:28 PM Roman Gushchin <[email protected]> wrote:
>
> page_cgroup_ino() doesn't return a valid memcg pointer for non-compund

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

Reviewed-by: Shakeel Butt <[email protected]>

> Cc: Vladimir Davydov <[email protected]>
> Cc: Shakeel Butt <[email protected]>
> ---
> 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
>