linux-kernel - Re: memcg memory accounting in vmalloc is broken

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Message-ID: <YV7/mS8oIL4E5nmS@dhcp22.suse.cz>
Date:   Thu, 7 Oct 2021 16:09:29 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Vasily Averin <vvs@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kernel@...nvz.org, Mel Gorman <mgorman@...e.de>,
        Uladzislau Rezki <urezki@...il.com>
Subject: Re: memcg memory accounting in vmalloc is broken

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