linux-kernel - Re: [RFC PATCH] rework memory hotplug onlining

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Message-ID: <CAA9_cmffsak7vYnEkNmvmg6rrd_iECAJBmYU8eRU2HQwBWAi_w@mail.gmail.com>
Date:   Tue, 21 Mar 2017 07:09:15 -0700
From:   Dan Williams <dan.j.williams@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm <linux-mm@...ck.org>, Mel Gorman <mgorman@...e.de>,
        qiuxishi@...wei.com, Toshi Kani <toshi.kani@....com>,
        xieyisheng1@...wei.com, slaoub@...il.com,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Zhang Zhen <zhenzhang.zhang@...wei.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        Tang Chen <tangchen@...fujitsu.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RFC PATCH] rework memory hotplug onlining

On Fri, Mar 17, 2017 at 6:20 AM, Michal Hocko <mhocko@...nel.org> wrote:
> On Wed 15-03-17 10:13:47, Michal Hocko wrote:
> [...]
>> It seems that all this is just started by the semantic introduced by
>> 9d99aaa31f59 ("[PATCH] x86_64: Support memory hotadd without sparsemem")
>> quite some time ago. When the movable onlinining has been introduced it
>> just built on top of this. It seems that the requirement to have
>> freshly probed memory associated with the zone normal is no longer
>> necessary. HOTPLUG depends on CONFIG_SPARSEMEM these days.
>>
>> The following blob [2] simply removes all the zone specific operations
>> from __add_pages (aka arch_add_memory) path.  Instead we do page->zone
>> association from move_pfn_range which is called from online_pages. The
>> criterion for movable/normal zone association is really simple now. We
>> just have to guarantee that zone Normal is always lower than zone
>> Movable. It would be actually sufficient to guarantee they do not
>> overlap and that is indeed trivial to implement now. I didn't do that
>> yet for simplicity of this change though.
>
> Does anybody have any comments on this? Any issues I've overlooked
> (except for the one pointed by Toshi Kani which is already fixed in my
> local branch)?

It disables the ZONE_DEVICE use case, but like we chatted about at LSF
I'll take a look at having devm_memremap_pages() call
move_pfn_range().