From: Michal Hocko <firstname.lastname@example.org>
To: Muchun Song <email@example.com>
Cc: Roman Gushchin <firstname.lastname@example.org>,
Johannes Weiner <email@example.com>,
Andrew Morton <firstname.lastname@example.org>,
Shakeel Butt <email@example.com>,
Vladimir Davydov <firstname.lastname@example.org>,
Linux Memory Management List <email@example.com>
Subject: Re: [External] Re: [PATCH] mm: memcontrol: fix memsw uncharge for root_mem_cgroup
Date: Wed, 24 Mar 2021 10:20:25 +0100 [thread overview]
Message-ID: <YFsEWfzxB3iPc66Y@dhcp22.suse.cz> (raw)
On Wed 24-03-21 16:50:41, Muchun Song wrote:
> On Wed, Mar 24, 2021 at 4:33 PM Michal Hocko <firstname.lastname@example.org> wrote:
> > On Wed 24-03-21 12:11:35, Muchun Song wrote:
> > > On Tue, Mar 23, 2021 at 11:04 PM Muchun Song <email@example.com> wrote:
> > > >
> > > > The pages aren't accounted at the root level, so we cannot uncharge the
> > > > page to the memsw counter for the root memcg. Fix this.
> > > >
> > > > Fixes: 1f47b61fb407 ("mm: memcontrol: fix swap counter leak on swapout from offline cgroup")
> > > > Signed-off-by: Muchun Song <firstname.lastname@example.org>
> > >
> > > I am very sorry. I should repent. I suddenly realise the fix is totally
> > > wrong. Because the @memcg cannot be root memcg when
> > > @memcg != @swap_memcg.
> > I am probably blind but I do not see why this would be the case.
> > We have memcg != swap_memcg in this branch but we do not know the
> > neither of the two is root_mem_cgroup, no? If we did knot that we
> > wouldn't have to check for swap_memcg != root_mem_cgroup. Or do I miss
> > something?
> I look at the mem_cgroup_id_get_online() closely. If memcg is root, this
> function always returns root memcg. So memcg will equal swap_memcg.
Ahh, I can see it now. I have completely missed that the swap_memcg is
a parent of an offline memcg. I should have looked more closely.
prev parent reply other threads:[~2021-03-24 9:20 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-23 14:56 [PATCH] mm: memcontrol: fix memsw uncharge for root_mem_cgroup Muchun Song
2021-03-23 16:11 ` Michal Hocko
2021-03-24 4:11 ` Muchun Song
2021-03-24 8:33 ` Michal Hocko
2021-03-24 8:50 ` [External] " Muchun Song
2021-03-24 9:20 ` Michal Hocko [this message]
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