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

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Date:   Wed, 18 Mar 2020 13:20:08 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Christopher Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline

* Michal Hocko <mhocko@...nel.org> [2020-03-16 09:54:25]:

> On Sun 15-03-20 14:20:05, Cristopher Lameter wrote:
> > On Wed, 11 Mar 2020, Srikar Dronamraju wrote:
> > 
> > > Currently Linux kernel with CONFIG_NUMA on a system with multiple
> > > possible nodes, marks node 0 as online at boot.  However in practice,
> > > there are systems which have node 0 as memoryless and cpuless.
> > 
> > Would it not be better and simpler to require that node 0 always has
> > memory (and processors)? A  mininum operational set?
> 
> I do not think you can simply ignore the reality. I cannot say that I am
> a fan of memoryless/cpuless numa configurations but they are a sad
> reality of different LPAR configurations. We have to deal with them.
> Besides that I do not really see any strong technical arguments to lack
> a support for those crippled configurations. We do have zonelists that
> allow to do reasonable decisions on memoryless nodes. So no, I do not
> think that this is a viable approach.
> 

I agree with Michal, kernel should accept the reality and work with
different Lpar configurations.

> > We can dynamically number the nodes right? So just make sure that the
> > firmware properly creates memory on node 0?
> 
> Are you suggesting that the OS would renumber NUMA nodes coming
> from FW just to satisfy node 0 existence? If yes then I believe this is
> really a bad idea because it would make HW/LPAR configuration matching
> to the resulting memory layout really hard to follow.
> 
> -- 
> Michal Hocko
> SUSE Labs

Michal, Vlastimil, Christoph and others, do you have any more comments,
suggestions or any other feedback. If not, can you please add your
reviewed-by, acked etc.

-- 
Thanks and Regards
Srikar Dronamraju