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From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Yafang Shao <laoar.shao@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Muchun Song <songmuchun@bytedance.com>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH] mm: memcontrol: do not miss MEMCG_MAX events for
 enforced allocations
Message-ID: <YsBmoqEBCa7ra7w2@castle>
References: <20220702033521.64630-1-roman.gushchin@linux.dev>
 <CALvZod7TGhWtcRD6HeEx90T2+Rod-yamq9i+WbEQUKwNFTi-1A@mail.gmail.com>
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On Fri, Jul 01, 2022 at 10:50:40PM -0700, Shakeel Butt wrote:
> On Fri, Jul 1, 2022 at 8:35 PM Roman Gushchin <roman.gushchin@linux.dev> wrote:
> >
> > Yafang Shao reported an issue related to the accounting of bpf
> > memory: if a bpf map is charged indirectly for memory consumed
> > from an interrupt context and allocations are enforced, MEMCG_MAX
> > events are not raised.
> >
> > It's not/less of an issue in a generic case because consequent
> > allocations from a process context will trigger the reclaim and
> > MEMCG_MAX events. However a bpf map can belong to a dying/abandoned
> > memory cgroup, so it might never happen.
> 
> The patch looks good but the above sentence is confusing. What might
> never happen? Reclaim or MAX event on dying memcg?

Direct reclaim and MAX events. I agree it might be not clear without
looking into the code. How about something like this?

"It's not/less of an issue in a generic case because consequent
allocations from a process context will trigger the direct reclaim
and MEMCG_MAX events will be raised. However a bpf map can belong
to a dying/abandoned memory cgroup, so there will be no allocations
from a process context and no MEMCG_MAX events will be triggered."

Thanks!