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

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Message-ID: <20170407171055.GA16527@redhat.com>
Date:   Fri, 7 Apr 2017 13:10:59 -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 06:37:37PM +0200, Michal Hocko wrote:
> On Fri 07-04-17 12:10:00, Jerome Glisse wrote:
> > On Fri, Apr 07, 2017 at 05:11:05PM +0200, Michal Hocko wrote:
> > > On Fri 07-04-17 10:57:43, Jerome Glisse wrote:
> > > > On Fri, Apr 07, 2017 at 04:45:04PM +0200, Michal Hocko wrote:
> > > > > On Fri 07-04-17 10:32:49, Jerome Glisse wrote:
> > > > > > 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.
> > > > > 
> > > > > Why don't you use __add_pages directly then?
> > > > 
> > > > That's a possibility, i wanted to keep the arch code in the loop in case
> > > > some arch wanted to do something specific. But it is unlikely to ever be
> > > > use outside x86 and i don't think we will want to do anything more than
> > > > skipping linear mapping.
> > > 
> > > Hmm, I am looking closer and x86 stil updates max_pfn. Is this needed
> > > or you are guaranteed to not cross the max_pfn?
> > 
> > No guaranteed so yes i somewhat care about max_pfn, i do not care about
> > any of its existing user last time i check but it might matter for some
> > new user.
> 
> OK, then we can add add_pages() which would do __add_pages by default
> (#ifndef ARCH_HAS_ADD_PAGES) and x86 would override it do also call
> update_end_of_memory_vars. This sounds easier to me than updating all
> the archs and add something that most of them do not really care about.
> 
> But I will not insist. If you think that your approach is better I will
> not object.

Something like attached patch ?

> 
> Btw. is your series reviewed and ready to be applied to the mm tree? I
> planed to post mine on Monday so I would like to know how do we
> coordinate. I rebase on topo of yours or vice versa.

Well v18 core patches were review by Mel, i did include all of his comment
in v19 (i don't think i did miss any). I think Dan still want to look at
patch 1 and 3 for ZONE_DEVICE.

But i always welcome more review. I know Anshuman replied to this patch
to improve a comments. Balbir had issue on powerpc because iomem_resource.end
isn't clamped to MAX_PHYSMEM_BITS But that is all review i got so far on v19.

I don't mind rebasing on top of your patchset. What ever is easier for
Andrew i guess.

Cheers,
Jérôme

View attachment "0001-mm-memory_hotplug-add-add_pages-hotplug-without-line.patch" of type "text/plain" (3279 bytes)