Re: memcg memory accounting in vmalloc is broken

Michal Hocko
2021-10-07T14:09:29Z

On Thu 07-10-21 16:00:21, Vlastimil Babka wrote:
> On 10/7/21 10:50, Vasily Averin wrote:
> > On 10/7/21 11:16 AM, Michal Hocko wrote:
> >> Cc Mel and Uladzislau
> >>
> >> On Thu 07-10-21 10:13:23, Michal Hocko wrote:
> >>> On Thu 07-10-21 11:04:40, Vasily Averin wrote:
> >>>> vmalloc was switched to __alloc_pages_bulk but it does not account the memory to memcg.
> >>>>
> >>>> Is it known issue perhaps?
> >>>
> >>> No, I think this was just overlooked. Definitely doesn't look
> >>> intentional to me.
> >
> > I use following patch as a quick fix,
> > it helps though it is far from ideal and can be optimized.
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index b37435c274cf..e6abe2cac159 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5290,6 +5290,12 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
> >
> > page = __rmqueue_pcplist(zone, 0, ac.migratetype, alloc_flags,
> > pcp, pcp_list);
> > +
> > + if (memcg_kmem_enabled() && (gfp & __GFP_ACCOUNT) && page &&
> > + unlikely(__memcg_kmem_charge_page(page, gfp, 0) != 0)) {
> > + __free_pages(page, 0);
>
> It's too early for this here, we didn't go through prep_new_page() yet,
> minimally the post_alloc_hook() -> set_page_refcounted() part, required for
> put_page_testzero() in __free_pages() to work properly, and probably other
> stuff.
> Either do the full prep+free or a minimal reversion of __rmqueue_pcplist -
> something to just put the page back to pcplist. Probably the former so we
> don't introduce subtle errors.

Very well spotted!
--
Michal Hocko
SUSE Labs