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From: Dan Williams <dan.j.williams@gmail.com>
Date: Tue, 21 Mar 2017 07:09:15 -0700
Message-ID: <CAA9_cmffsak7vYnEkNmvmg6rrd_iECAJBmYU8eRU2HQwBWAi_w@mail.gmail.com>
Subject: Re: [RFC PATCH] rework memory hotplug onlining
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm <linux-mm@kvack.org>, Mel Gorman <mgorman@suse.de>,
        qiuxishi@huawei.com, Toshi Kani <toshi.kani@hpe.com>,
        xieyisheng1@huawei.com, slaoub@gmail.com,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Zhang Zhen <zhenzhang.zhang@huawei.com>,
        Reza Arbab <arbab@linux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@gmail.com>,
        Tang Chen <tangchen@cn.fujitsu.com>, Vlastimil Babka <vbabka@suse.cz>,
        Andrea Arcangeli <aarcange@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Daniel Kiper <daniel.kiper@oracle.com>,
        Igor Mammedov <imammedo@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Andi Kleen <ak@linux.intel.com>
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On Fri, Mar 17, 2017 at 6:20 AM, Michal Hocko <mhocko@kernel.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().