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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170407163737.GI16413@dhcp22.suse.cz>
Date:   Fri, 7 Apr 2017 18:37:37 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Jerome Glisse <jglisse@...hat.com>
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 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.

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.

Thanks!
-- 
Michal Hocko
SUSE Labs