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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 12 Oct 2021 09:08:38 -0700
Message-ID: <CALvZod7LpEY98r=pD-k=WbOT-z=Ux16Mfmv3s7PDtJg6=ZStgw@mail.gmail.com>
Subject: Re: [PATCH mm v3] memcg: enable memory accounting in __alloc_pages_bulk
To:     Michal Hocko <mhocko@suse.com>
Cc:     Vasily Averin <vvs@virtuozzo.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Roman Gushchin <guro@fb.com>,
        Uladzislau Rezki <urezki@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, kernel@openvz.org
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Precedence: bulk

On Tue, Oct 12, 2021 at 8:36 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Tue 12-10-21 17:58:21, Vasily Averin wrote:
> > Enable memory accounting for bulk page allocator.
>
> ENOCHANGELOG
>
> And I have to say I am not very happy about the solution. It adds a very
> tricky code where it splits different charging steps apart.
>
> Would it be just too inefficient to charge page-by-page once all pages
> are already taken away from the pcp lists? This bulk should be small so
> this shouldn't really cause massive problems. I mean something like
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b37435c274cf..8bcd69195ef5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5308,6 +5308,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
>
>         local_unlock_irqrestore(&pagesets.lock, flags);
>
> +       if (memcg_kmem_enabled() && (gfp & __GFP_ACCOUNT)) {
> +               /* charge pages here */
> +       }

It is not that simple because __alloc_pages_bulk only allocate pages
for empty slots in the page_array provided by the caller.

The failure handling for post charging would be more complicated.