linux-kernel - Re: [PATCH] mm/page_alloc: Deprecate kernelcore=nn and movable

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Message-ID: <alpine.DEB.2.21.1807181314230.49359@chino.kir.corp.google.com>
Date:   Wed, 18 Jul 2018 13:16:28 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Baoquan He <bhe@...hat.com>
cc:     mhocko@...nel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, corbet@....net,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: Deprecate kernelcore=nn and
 movable_core=

On Wed, 18 Jul 2018, Baoquan He wrote:

> > > We can still use 'kernelcore=mirror' or 'movable_node' for the usage
> > > of hotplug and movable zone. If somebody shows up with a valid usecase
> > > we can reconsider.
> > > 
> > 
> > We actively use kernelcore=n%, I had recently added support for the option 
> > in the first place in 4.17.  It's certainly not deprecated.
> 
> Thanks for telling. Just for curiosity, could you tell the scenario you
> are using kernelcore=n%? Since it evenly spread movable area on nodes,
> we may not be able to physically hot unplug/plug RAM.
> 

To evenly distribute ZONE_MOVABLE over a set of nodes regardless of the 
many memory capacities of systems that we have where individual command 
lines cannot be tuned.  But you want to deprecate kernelcore=nn, not just 
the percent version, so I assume that's not the answer you're looking for. 
We do not enable CONFIG_MEMORY_HOTPLUG so this deprecation would break our 
userspace such that we cannot use ZONE_MOVABLE.