Re: [HMM 01/16] mm/memory/hotplug: add memory type parameter to arch_add/remove_memory

[Michal Hocko]

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@xxxxxxxxxx
> > > > > > [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