Re: [PATCH] mm: correctly charge compressed memory to its memcg

[Yosry Ahmed <yosryahmed@google.com>]

On Fri, Aug 12, 2022 at 2:56 PM Shakeel Butt <shakeelb@google.com> wrote:
>
> +Andrew & linux-mm
>
> On Thu, Aug 11, 2022 at 5:12 PM Roman Gushchin <roman.gushchin@linux.dev> wrote:
> >
> > On Thu, Aug 11, 2022 at 04:19:13PM +0800, liliguang wrote:
> > > From: Li Liguang <liliguang@baidu.com>
> > >
> > > Kswapd will reclaim memory when memory pressure is high, the
> > > annonymous memory will be compressed and stored in the zpool
> > > if zswap is enabled. The memcg_kmem_bypass() in
> > > get_obj_cgroup_from_page() will bypass the kernel thread and
> > > cause the compressed memory not charged to its memory cgroup.
> > >
> > > Remove the memcg_kmem_bypass() and properly charge compressed
> > > memory to its corresponding memory cgroup.
> > >
> > > Signed-off-by: Li Liguang <liliguang@baidu.com>
> > > ---
> > >  mm/memcontrol.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index b69979c9ced5..6a95ea7c5ee7 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -2971,7 +2971,7 @@ struct obj_cgroup *get_obj_cgroup_from_page(struct page *page)
> > >  {
> > >       struct obj_cgroup *objcg;
> > >
> > > -     if (!memcg_kmem_enabled() || memcg_kmem_bypass())
> > > +     if (!memcg_kmem_enabled())


Won't the memcg_kmem_enabled() check also cause a problem in that same
scenario (e.g. if CONFIG_MEMCG_KMEM=n)? or am I missing something
here?

>
> > >               return NULL;
> > >
> > >       if (PageMemcgKmem(page)) {
> > > --
> > > 2.32.0 (Apple Git-132)
> > >
> >
> > Hi Li!
> >
> > The fix looks good to me! As we get objcg pointer from a page and not from
> > the current task, memcg_kmem_bypass() doesn't makes much sense.
> >
> > Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
> >
> > Probably, we need to add
> > Fixes: f4840ccfca25 ("zswap: memcg accounting")
> >
> > Thank you!
>
> You can add:
>
> Acked-by: Shakeel Butt <shakeelb@google.com>
>