Date:   Wed, 15 Dec 2021 13:20:58 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     linux-kernel@vger.kernel.org
Cc:     Dennis Zhou <dennis@kernel.org>,
        Alexey Makhalov <amakhalov@vmware.com>,
        "cl@linux.com" <cl@linux.com>,
        "mm-commits@vger.kernel.org" <mm-commits@vger.kernel.org>,
        "osalvador@suse.de" <osalvador@suse.de>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "tj@kernel.org" <tj@kernel.org>
Subject: Re: + mm-fix-panic-in-__alloc_pages.patch added to -mm tree
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On Wed 15-12-21 11:05:12, Michal Hocko wrote:
> On Tue 14-12-21 12:57:48, Andrew Morton wrote:
> > On Tue, 14 Dec 2021 11:11:54 +0100 Michal Hocko <mhocko@suse.com> wrote:
> > 
> > > > I need some clarification here. It sounds like memoryless nodes work on
> > > > x86, but hotplug + memoryless nodes isn't a supported use case or you're
> > > > introducing it as a new use case?
> > > > 
> > > > If this is a new use case, then I'm inclined to say this patch should
> > > > NOT go in and a proper fix should be implemented on hotplug's side. I
> > > > don't want to be in the business of having/seeing this conversation
> > > > reoccur because we just papered over this issue in percpu.
> > > 
> > > The patch still seems to be in the mmotm tree. I have sent a different
> > > fix candidate [1] which should be more robust and cover also other potential
> > > places.
> > > 
> > > [1] http://lkml.kernel.org/r/20211214100732.26335-1-mhocko@kernel.org
> > 
> > Is cool, I'm paying attention.
> > 
> > We do want something short and simple for backporting to -stable (like
> > Alexey's patch) so please bear that in mind while preparing an
> > alternative.
> 
> I think we want something that fixes the underlying problem. Please keep
> in mind that the pcp allocation is not the only place to hit the issue.
> We have more. I do not want we want to handle each and every one
> separately.
> 
> I am definitly not going to push for my solution but if there is a
> consensus this is the right approach then I do not think we really want
> to implement these partial workarounds.

Btw. I forgot to add that if we do not agree on the preallocation
approach then the approach should be something like 
http://lkml.kernel.org/r/51c65635-1dae-6ba4-daf9-db9df0ec35d8@redhat.com
proposed by David.
-- 
Michal Hocko
SUSE Labs