linux-kernel - Re: [HMM 01/16] mm/memory/hotplug: add memory type parameter to arch_add/remove

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Message-ID: <20170407143246.GA15098@redhat.com>
Date:   Fri, 7 Apr 2017 10:32:49 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, John Hubbard <jhubbard@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        David Nellans <dnellans@...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 01/16] mm/memory/hotplug: add memory type parameter to
 arch_add/remove_memory

On Fri, Apr 07, 2017 at 02:13:49PM +0200, Michal Hocko wrote:
> On Wed 05-04-17 16:40:11, Jérôme Glisse wrote:
> > When hotpluging memory we want more information on the type of memory.
> > This is to extend ZONE_DEVICE to support new type of memory other than
> > the persistent memory. Existing user of ZONE_DEVICE (persistent memory)
> > will be left un-modified.
> 
> My current hotplug rework [1] is touching this path as well. It is not
> really clear from the chage why you are changing this and what are the
> further expectations of MEMORY_DEVICE_PERSISTENT. Infact I have replaced
> for_device with want__memblock [2]. I plan to repost shortly but I would
> like to understand your modifications more to reduce potential conflicts
> in the code. Why do you need to distinguish different types of memory
> anyway.
> 
> [1] http://lkml.kernel.org/r/20170330115454.32154-1-mhocko@kernel.org
> [2] the current patchset is in git://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git
>     branch attempts/rewrite-mem_hotplug-WIP

This is needed for UNADDRESSABLE memory type introduced in patch 3 and
the arch specific bits are in patch 4. Basicly for UNADDRESSABLE memory
i do not want the arch code to create a linear mapping for the range
being hotpluged. Adding memory_type in this patch allow to distinguish
between different type of ZONE_DEVICE.

After your patchset, we do not need the for_device but i still need to
know if it is UNADDRESSABLE. You can check my branch on top of your
previous patchset (again patch 1, 3 and 4):

https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v20

1:
https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v20&id=a85a895615e4812d3c68869cfeef92a4924b4946
3:
https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v20&id=539b6d12429a7166f3690944d6bf164930a59def
4:
https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v20&id=d5338b868e801acabb96c7166c1e802d730511e3

I will check your new branch and see what want_memblock is for.

Cheers,
Jérôme