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[209.132.183.28]) by mx.google.com with ESMTPS id k6si28998257qki.23.2019.07.25.02.30.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Jul 2019 02:30:27 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D0E5B31628FF; Thu, 25 Jul 2019 09:30:26 +0000 (UTC) Received: from [10.36.117.212] (ovpn-117-212.ams2.redhat.com [10.36.117.212]) by smtp.corp.redhat.com (Postfix) with ESMTP id 943B85C6E3; Thu, 25 Jul 2019 09:30:24 +0000 (UTC) Subject: Re: [PATCH v2 2/5] mm,memory_hotplug: Introduce MHP_VMEMMAP_FLAGS To: Oscar Salvador , Dan Williams Cc: Andrew Morton , Michal Hocko , Pavel Tatashin , Jonathan Cameron , Anshuman Khandual , Vlastimil Babka , Linux MM , Linux Kernel Mailing List References: <20190625075227.15193-1-osalvador@suse.de> <20190625075227.15193-3-osalvador@suse.de> <20190725092751.GA15964@linux> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190725092751.GA15964@linux> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Thu, 25 Jul 2019 09:30:27 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 25.07.19 11:27, Oscar Salvador wrote: > On Wed, Jul 24, 2019 at 01:11:52PM -0700, Dan Williams wrote: >> On Tue, Jun 25, 2019 at 12:53 AM Oscar Salvador wrote: >>> >>> This patch introduces MHP_MEMMAP_DEVICE and MHP_MEMMAP_MEMBLOCK flags, >>> and prepares the callers that add memory to take a "flags" parameter. >>> This "flags" parameter will be evaluated later on in Patch#3 >>> to init mhp_restrictions struct. >>> >>> The callers are: >>> >>> add_memory >>> __add_memory >>> add_memory_resource >>> >>> Unfortunately, we do not have a single entry point to add memory, as depending >>> on the requisites of the caller, they want to hook up in different places, >>> (e.g: Xen reserve_additional_memory()), so we have to spread the parameter >>> in the three callers. >>> >>> The flags are either MHP_MEMMAP_DEVICE or MHP_MEMMAP_MEMBLOCK, and only differ >>> in the way they allocate vmemmap pages within the memory blocks. >>> >>> MHP_MEMMAP_MEMBLOCK: >>> - With this flag, we will allocate vmemmap pages in each memory block. >>> This means that if we hot-add a range that spans multiple memory blocks, >>> we will use the beginning of each memory block for the vmemmap pages. >>> This strategy is good for cases where the caller wants the flexiblity >>> to hot-remove memory in a different granularity than when it was added. >>> >>> E.g: >>> We allocate a range (x,y], that spans 3 memory blocks, and given >>> memory block size = 128MB. >>> [memblock#0 ] >>> [0 - 511 pfns ] - vmemmaps for section#0 >>> [512 - 32767 pfns ] - normal memory >>> >>> [memblock#1 ] >>> [32768 - 33279 pfns] - vmemmaps for section#1 >>> [33280 - 65535 pfns] - normal memory >>> >>> [memblock#2 ] >>> [65536 - 66047 pfns] - vmemmap for section#2 >>> [66048 - 98304 pfns] - normal memory >>> >>> MHP_MEMMAP_DEVICE: >>> - With this flag, we will store all vmemmap pages at the beginning of >>> hot-added memory. >>> >>> E.g: >>> We allocate a range (x,y], that spans 3 memory blocks, and given >>> memory block size = 128MB. >>> [memblock #0 ] >>> [0 - 1533 pfns ] - vmemmap for section#{0-2} >>> [1534 - 98304 pfns] - normal memory >>> >>> When using larger memory blocks (1GB or 2GB), the principle is the same. >>> >>> Of course, MHP_MEMMAP_DEVICE is nicer when it comes to have a large contigous >>> area, while MHP_MEMMAP_MEMBLOCK allows us to have flexibility when removing the >>> memory. >> >> Concept and patch looks good to me, but I don't quite like the >> proliferation of the _DEVICE naming, in theory it need not necessarily >> be ZONE_DEVICE that is the only user of that flag. I also think it >> might be useful to assign a flag for the default 'allocate from RAM' >> case, just so the code is explicit. So, how about: > > Well, MHP_MEMMAP_DEVICE is not tied to ZONE_DEVICE. > MHP_MEMMAP_DEVICE was chosen to make a difference between: > > * allocate memmap pages for the whole memory-device > * allocate memmap pages on each memoryblock that this memory-device spans I agree that DEVICE is misleading here, you are assuming a one-to-one mapping between a device and add_memory(). You are actually taliing about "allocate a single chunk of mmap pages for the whole memory range that is added - which could consist of multiple memory blocks". -- Thanks, David / dhildenb