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Subject: Re: [RFC PATCH 0/7] Memory hotplug/hotremove at subsection size
To:     Zi Yan <ziy@nvidia.com>, Oscar Salvador <osalvador@suse.de>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@kernel.org>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Michal Hocko <mhocko@suse.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Wei Yang <richard.weiyang@linux.alibaba.com>,
        linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org
References: <20210506152623.178731-1-zi.yan@sent.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <fb60eabd-f8ef-2cb1-7338-7725efe3c286@redhat.com>
Date:   Thu, 6 May 2021 17:31:09 +0200
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On 06.05.21 17:26, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> Hi all,
> 
> This patchset tries to remove the restriction on memory hotplug/hotremove
> granularity, which is always greater or equal to memory section size[1].
> With the patchset, kernel is able to online/offline memory at a size independent
> of memory section size, as small as 2MB (the subsection size).

... which doesn't make any sense as we can only online/offline whole 
memory block devices.

> 
> The motivation is to increase MAX_ORDER of the buddy allocator and pageblock
> size without increasing memory hotplug/hotremove granularity at the same time,

Gah, no. Please no. No.

> so that the kernel can allocator 1GB pages using buddy allocator and utilizes
> existing pageblock based anti-fragmentation, paving the road for 1GB THP
> support[2].

Not like this, please no.

> 
> The patchset utilizes the existing subsection support[3] and changes the
> section size alignment checks to subsection size alignment checks. There are
> also changes to pageblock code to support partial pageblocks, when pageblock
> size is increased along with MAX_ORDER. Increasing pageblock size can enable
> kernel to utilize existing anti-fragmentation mechanism for gigantic page
> allocations.

Please not like this.

> 
> The last patch increases SECTION_SIZE_BITS to demonstrate the use of memory
> hotplug/hotremove subsection, but is not intended to be merged as is. It is
> there in case one wants to try this out and will be removed during the final
> submission.
> 
> Feel free to give suggestions and comments. I am looking forward to your
> feedback.

Please not like this.

-- 
Thanks,

David / dhildenb