From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Date: Thu, 06 May 2021 15:31:09 +0000 Subject: Re: [RFC PATCH 0/7] Memory hotplug/hotremove at subsection size Message-Id: List-Id: References: <20210506152623.178731-1-zi.yan@sent.com> In-Reply-To: <20210506152623.178731-1-zi.yan@sent.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Zi Yan , Oscar Salvador Cc: Michael Ellerman , Benjamin Herrenschmidt , Thomas Gleixner , x86@kernel.org, Andy Lutomirski , "Rafael J . Wysocki" , Andrew Morton , Mike Rapoport , Anshuman Khandual , Michal Hocko , Dan Williams , Wei Yang , linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org On 06.05.21 17:26, Zi Yan wrote: > From: Zi Yan > > 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