Re: [PATCH v2] memcg: add per-memcg vmalloc stat

[Shakeel Butt <shakeelb@google.com>]

On Wed, Dec 22, 2021 at 6:03 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Tue, Dec 21, 2021 at 09:24:57PM -0800, Shakeel Butt wrote:
> > The kvmalloc* allocation functions can fallback to vmalloc allocations
> > and more often on long running machines. In addition the kernel does
> > have __GFP_ACCOUNT kvmalloc* calls. So, often on long running machines,
> > the memory.stat does not tell the complete picture which type of memory
> > is charged to the memcg. So add a per-memcg vmalloc stat.
> >
> > Signed-off-by: Shakeel Butt <shakeelb@google.com>
> >
> > ---
> > Changelog since v1:
> > - page_memcg() within rcu lock as suggested by Muchun.
> >
> >  Documentation/admin-guide/cgroup-v2.rst |  3 +++
> >  include/linux/memcontrol.h              | 21 +++++++++++++++++++++
> >  mm/memcontrol.c                         |  1 +
> >  mm/vmalloc.c                            |  5 +++++
> >  4 files changed, 30 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> > index 82c8dc91b2be..5aa368d165da 100644
> > --- a/Documentation/admin-guide/cgroup-v2.rst
> > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > @@ -1314,6 +1314,9 @@ PAGE_SIZE multiple when read back.
> >         sock (npn)
> >               Amount of memory used in network transmission buffers
> >
> > +       vmalloc (npn)
> > +             Amount of memory used for vmap backed memory.
> > +
>
> It's a bid sad that this counter will partially intersect with others
> (e.g. percpu and stack), but I don't see how it can be easily fixed.

I checked those again. For vmap based stack we do vmalloc() without
__GFP_ACCOUNT and charge the stack page afterwards with
memcg_kmem_charge_page() interface.

I think we do the same for percpu as well i.e. not use GFP_ACCOUNT for
underlying memory but later use objcg infrastructure to charge at
finer grain.

So, I think at least percpu and stack should not intersect with
vmalloc per-memcg stat.

>
> But I agree that the counter is useful and worth adding.
>
> Acked-by: Roman Gushchin <guro@fb.com>

Thanks.