linux-kernel - Re: [HMM v16 01/15] mm/memory/hotplug: convert device bool to int to allow for more flags v2

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Message-ID: <20170113144508.GA3758@redhat.com>
Date:   Fri, 13 Jan 2017 09:45:08 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, John Hubbard <jhubbard@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [HMM v16 01/15] mm/memory/hotplug: convert device bool to int to
 allow for more flags v2

On Fri, Jan 13, 2017 at 07:27:41PM +0530, Balbir Singh wrote:
> On Thu, Jan 12, 2017 at 11:30:28AM -0500, Jérôme Glisse wrote:
> > When hotpluging memory we want more informations on the type of memory and
> > its properties. Replace the device boolean flag by an int and define a set
> > of flags.
> > 
> > New property for device memory is an opt-in flag to allow page migration
> > from and to a ZONE_DEVICE. Existing user of ZONE_DEVICE are not expecting
> > page migration to work for their pages. New changes to page migration i
> > changing that and we now need a flag to explicitly opt-in page migration.
> 
> Given that ZONE_DEVICE is dependent on X86_64, do we need to touch all
> architectures? I guess we could selectively enable things as we enable
> ZONE_DEVICE for other architectures?

Yes i need to change all architecture because the function prototype changes.

I add the bug stuff to be bullet proof from new feature added that might
cause trouble if arch does not handle them explicitly. If the bug stuff scares
people i can remove it.

Cheers,
Jérôme