From mboxrd@z Thu Jan  1 00:00:00 1970
From: Roman Gushchin <roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>
Subject: Re: [PATCH] mm: memcontrol: do not miss MEMCG_MAX events for
 enforced allocations
Date: Sat, 2 Jul 2022 08:39:14 -0700
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To: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Yafang Shao <laoar.shao-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Muchun Song <songmuchun-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux MM <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>, bpf <bpf-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>

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-fxUVXftIFDnyG1zEObXtfA@public.gmane.org> 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!