linux-kernel - Re: [PATCH 1/1] powerpc/kernel: Enables memory hot-remove after reboot on pseries guests

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Date:   Wed, 04 Mar 2020 04:18:32 -0300
From:   Leonardo Bras <leonardo@...ux.ibm.com>
To:     Bharata B Rao <bharata.rao@...il.com>
Cc:     ndfont@...il.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        arbab@...ux.ibm.com, Claudio Carvalho <cclaudio@...ux.ibm.com>,
        Michael Roth <mdroth@...ux.vnet.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Hari Bathini <hbathini@...ux.ibm.com>
Subject: Re: [PATCH 1/1] powerpc/kernel: Enables memory hot-remove after
 reboot on pseries guests

Hello Bharata, thanks for this feedback!

On Wed, 2020-03-04 at 10:13 +0530, Bharata B Rao wrote:
> Hi,
> 
> I tried this a few years back
> (https://patchwork.ozlabs.org/patch/800142/) and didn't pursue it
> further because at that time, it was felt that the approach might not
> work for PowerVM guests, because all the present memory except RMA
> gets marked as hot-pluggable by PowerVM. This discussion is not
> present in the above thread, but during my private discussions with
> Reza and Nathan, it was noted that making all that memory as MOVABLE
> is not preferable for PowerVM guests as we might run out of memory for
> kernel allocations.

Humm, this makes sense.
But with mu change, these pieces of memory only get into ZONE_MOVABLE
if the boot parameter 'movable_node' gets passed to guest kernel. 

So, even if we are unable to sort out some flag combination that work
fine for both use-cases, if PowerVM don't pass 'movable_node' as boot
parameter to kernel, it will behave just as today.

What are your thoughts on that?

Best regards,

Leonardo Bras

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