linux-kernel - Re: [PATCH mm v3] memcg: enable memory accounting in __alloc_pages

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Message-ID: <CALvZod5V_NK_mVFY7ik6wSWPxqSqRrhzJkdtuyQjzMB-0yjHGw@mail.gmail.com>
Date:   Wed, 13 Oct 2021 10:30:05 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Vasily Averin <vvs@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Roman Gushchin <guro@...com>,
        Uladzislau Rezki <urezki@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel@...nvz.org
Subject: Re: [PATCH mm v3] memcg: enable memory accounting in __alloc_pages_bulk

On Wed, Oct 13, 2021 at 10:16 AM Michal Hocko <mhocko@...e.com> wrote:
>
[...]
> > > If this is really that complicated (I haven't tried) then it would be
> > > much more simple to completely skip the bulk allocator for __GFP_ACCOUNT
> > > rather than add a tricky code. The bulk allocator is meant to be used
> > > for ultra hot paths and memcg charging along with the reclaim doesn't
> > > really fit into that model anyway. Or are there any actual users who
> > > really need bulk allocator optimization and also need memcg accounting?
> >
> > Bulk allocator is being used for vmalloc and we have several
> > kvmalloc() with __GFP_ACCOUNT allocations.
>
> Do we really need to use bulk allocator for these allocations?
> Bulk allocator is an bypass of the page allocator for performance reason
> and I can see why that can be useful but considering that the charging
> path can imply some heavy lifting is all the code churn to make bulk
> allocator memcg aware really worth it? Why cannot we simply skip over
> bulk allocator for __GFP_ACCOUNT. That would be a trivial fix.
> --

Actually that might be the simplest solution and I agree to skip bulk
allocator for __GFP_ACCOUNT allocations.