linux-kernel - Re: [PATCH v5 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline

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Message-ID: <20200818073712.GK28270@dhcp22.suse.cz>
Date:   Tue, 18 Aug 2020 09:37:12 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Such?nek <msuchanek@...e.de>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        linuxppc-dev@...ts.ozlabs.org, Christopher Lameter <cl@...ux.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andi Kleen <ak@...ux.intel.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH v5 3/3] mm/page_alloc: Keep memoryless cpuless node 0
 offline

On Tue 18-08-20 09:32:52, David Hildenbrand wrote:
> On 12.08.20 08:01, Srikar Dronamraju wrote:
> > Hi Andrew, Michal, David
> > 
> > * Andrew Morton <akpm@...ux-foundation.org> [2020-08-06 21:32:11]:
> > 
> >> On Fri, 3 Jul 2020 18:28:23 +0530 Srikar Dronamraju <srikar@...ux.vnet.ibm.com> wrote:
> >>
> >>>> The memory hotplug changes that somehow because you can hotremove numa
> >>>> nodes and therefore make the nodemask sparse but that is not a common
> >>>> case. I am not sure what would happen if a completely new node was added
> >>>> and its corresponding node was already used by the renumbered one
> >>>> though. It would likely conflate the two I am afraid. But I am not sure
> >>>> this is really possible with x86 and a lack of a bug report would
> >>>> suggest that nobody is doing that at least.
> >>>>
> >>>
> >>> JFYI,
> >>> Satheesh copied in this mailchain had opened a bug a year on crash with vcpu
> >>> hotplug on memoryless node. 
> >>>
> >>> https://bugzilla.kernel.org/show_bug.cgi?id=202187
> >>
> >> So...  do we merge this patch or not?  Seems that the overall view is
> >> "risky but nobody is likely to do anything better any time soon"?
> > 
> > Can we decide on this one way or the other?
> 
> Hmm, not sure who's the person to decide. I tend to prefer doing the
> node renaming, handling this in ppc code;

Agreed. That would be a safer option.
-- 
Michal Hocko
SUSE Labs