Re: [External] Re: [PATCH 4/5] mm: memcg/slab: Fix root memcg vmstats

[Muchun Song]

On Wed, Oct 28, 2020 at 10:56 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
>
> On Wed, Oct 28, 2020 at 2:48 AM Roman Gushchin <guro@xxxxxx> wrote:
> >
> > On Tue, Oct 27, 2020 at 04:02:55PM +0800, Muchun Song wrote:
> > > If we reparent the slab objects to the root memcg, when we free
> > > the slab object, we need to update the per-memcg vmstats to keep
> > > it correct for the root memcg. Now this at least affects the vmstat
> > > of NR_KERNEL_STACK_KB for !CONFIG_VMAP_STACK when the thread stack
> > > size is smaller than the PAGE_SIZE.
> > >
> > > Fixes: ec9f02384f60 ("mm: workingset: fix vmstat counters for shadow nodes")
> > > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> >
> > Can you, please, drop this patch for now?
> >
> > I'm working on a bigger cleanup related to the handling of the root memory
> > cgroup (I sent a link earlier in this thread), which already does a similar change.
> > There are several issues like this one, so it will be nice to fix them all at once.
>
> I have read the patch of https://lkml.org/lkml/2020/10/14/869. You
> mean this patch
> fixes this issue? It chooses to uncharge the root memcg. But here we may need to

Here I mean "It chooses to not uncharge the root memcg", sorry.

> uncharge the root memcg to keep root vmstats correct. If we do not do
> this, we can
> see the wrong vmstats via root memory.stat(e.g. NR_KERNEL_STACK_KB).
>
> Thanks.
>
> >
> > Thank you!
> >
> > > ---
> > >  mm/memcontrol.c | 9 +++++++--
> > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index 22b4fb941b54..70345b15b150 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -875,8 +875,13 @@ void __mod_lruvec_kmem_state(void *p, enum node_stat_item idx, int val)
> > >       rcu_read_lock();
> > >       memcg = mem_cgroup_from_obj(p);
> > >
> > > -     /* Untracked pages have no memcg, no lruvec. Update only the node */
> > > -     if (!memcg || memcg == root_mem_cgroup) {
> > > +     /*
> > > +      * Untracked pages have no memcg, no lruvec. Update only the
> > > +      * node. If we reparent the slab objects to the root memcg,
> > > +      * when we free the slab object, we need to update the per-memcg
> > > +      * vmstats to keep it correct for the root memcg.
> > > +      */
> > > +     if (!memcg) {
> > >               __mod_node_page_state(pgdat, idx, val);
> > >       } else {
> > >               lruvec = mem_cgroup_lruvec(memcg, pgdat);
> > > --
> > > 2.20.1
> > >
>
>
>
> --
> Yours,
> Muchun



-- 
Yours,
Muchun