From: Muchun Song <songmuchun@bytedance.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Andrew Morton <akpm@linux-foundation.org>,
Shakeel Butt <shakeelb@google.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [External] Re: [PATCH] mm: memcontrol: fix memsw uncharge for root_mem_cgroup
Date: Wed, 24 Mar 2021 16:50:41 +0800 [thread overview]
Message-ID: <CAMZfGtVe6seRLA7Wo4TST0ApkaHdkDmv6sL5GZytK_4hvMbkXg@mail.gmail.com> (raw)
In-Reply-To: <YFr5SrJ2iNGYwVNA@dhcp22.suse.cz>
On Wed, Mar 24, 2021 at 4:33 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Wed 24-03-21 12:11:35, Muchun Song wrote:
> > On Tue, Mar 23, 2021 at 11:04 PM Muchun Song <songmuchun@bytedance.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 <songmuchun@bytedance.com>
> >
> > 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.
I apologize for not carefully reviewing the code myself.
Thanks.
> --
> Michal Hocko
> SUSE Labs
next prev parent reply other threads:[~2021-03-24 8:51 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 ` Muchun Song [this message]
2021-03-24 9:20 ` [External] " Michal Hocko
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