Subject: Re: [PATCH 4/9] mm, memory_hotplug: get rid of is_zone_device_section
To: Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org
References: <20170410110351.12215-1-mhocko@kernel.org>
 <20170410110351.12215-5-mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Andrea Arcangeli <aarcange@redhat.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Reza Arbab <arbab@linux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, qiuxishi@huawei.com,
        Kani Toshimitsu <toshi.kani@hpe.com>, slaoub@gmail.com,
        Joonsoo Kim <js1304@gmail.com>, Andi Kleen <ak@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Daniel Kiper <daniel.kiper@oracle.com>,
        Igor Mammedov <imammedo@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, Michal Hocko <mhocko@suse.com>,
        Dan Williams <dan.j.williams@gmail.com>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <9e379e57-b700-0b48-6e45-a5f6e3cc9010@suse.cz>
Date: Thu, 13 Apr 2017 15:05:24 +0200
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On 04/10/2017 01:03 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> device memory hotplug hooks into regular memory hotplug only half way.
> It needs memory sections to track struct pages but there is no
> need/desire to associate those sections with memory blocks and export
> them to the userspace via sysfs because they cannot be onlined anyway.
> 
> This is currently expressed by for_device argument to arch_add_memory
> which then makes sure to associate the given memory range with
> ZONE_DEVICE. register_new_memory then relies on is_zone_device_section
> to distinguish special memory hotplug from the regular one. While this
> works now, later patches in this series want to move __add_zone outside
> of arch_add_memory path so we have to come up with something else.
> 
> Add want_memblock down the __add_pages path and use it to control
> whether the section->memblock association should be done. arch_add_memory
> then just trivially want memblock for everything but for_device hotplug.
> 
> remove_memory_section doesn't need is_zone_device_section either. We can
> simply skip all the memblock specific cleanup if there is no memblock
> for the given section.
> 
> This shouldn't introduce any functional change.
> 
> Cc: Dan Williams <dan.j.williams@gmail.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>

For the fixed version:

Acked-by: Vlastimil Babka <vbabka@suse.cz>