Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker_info on offlined nodes

From: Michal Hocko <mhocko@suse.com>
To: Yang Shi <shy828301@gmail.com>
Cc: Nico Pache <npache@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>, Shakeel Butt <shakeelb@google.com>,
	Kirill Tkhai <ktkhai@virtuozzo.com>, Roman Gushchin <guro@fb.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	raquini@redhat.com, David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker_info on offlined nodes
Date: Wed, 8 Dec 2021 08:59:36 +0100	[thread overview]
Message-ID: <YbBl6O8wzgVQb6Oi@dhcp22.suse.cz> (raw)
In-Reply-To: <CAHbLzkpG4aogZRW5ct9zKDU+5C8jwtWyRAkaia1x3+goR-wGMg@mail.gmail.com>

On Tue 07-12-21 17:26:32, Yang Shi wrote:
> On Tue, Dec 7, 2021 at 5:23 PM Yang Shi <shy828301@gmail.com> wrote:
> >
> > On Tue, Dec 7, 2021 at 4:33 PM Nico Pache <npache@redhat.com> wrote:
> > >
> > >
> > >
> > > On 12/7/21 19:26, Yang Shi wrote:
[...]
> > > > AFAICT, we have not reached agreement on how to fix it yet. I saw 3
> > > > proposals at least:
> > > >
> > > > 1. From Michal, allocate node data for all possible nodes.
> > > > https://lore.kernel.org/all/Ya89aqij6nMwJrIZ@dhcp22.suse.cz/T/#u
> > > >
> > > > 2. What this patch does. Proposed originally from
> > > > https://lore.kernel.org/all/20211108202325.20304-1-amakhalov@vmware.com/T/#u
> > >
> > > Correct me if im wrong, but isn't that a different caller? This patch fixes the
> > > issue in expand_one_shrinker_info.
> >
> > Yes, different caller, but same approach. The cons with this approach
> 
> And the same underlying problem.
> 
> > is we have to fix all the places. It seems Michal and David are not
> > fans for this approach IIRC.

Yes, agreed. We definitely do not want to spread this node_offline
oddity all over the place. There are two different way to approach this.
Either we handle node_offline nodes at the page allocator level when
setting the proper zonelist (ideally protect that by a static key for
setups which have these nodes) or we allocate pgdat for all possible
nodes. I would prefer the second because that is more robust (less
likely to blow up when somebody does
	for_each_node(nid)
		something(NODE_DATA(nid))

The discussion is ongoing at the original thread where Alexey Makhalov
reported a similar problem (the subthread is
http://lkml.kernel.org/r/Ya89aqij6nMwJrIZ@dhcp22.suse.cz)
-- 
Michal Hocko
SUSE Labs