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[209.132.183.28]) by mx.google.com with ESMTPS id 25si920123qts.195.2019.03.29.02.01.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 Mar 2019 02:01:30 -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-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id ED0F1308FC5E; Fri, 29 Mar 2019 09:01:29 +0000 (UTC) Received: from [10.36.117.0] (unknown [10.36.117.0]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5ABD060851; Fri, 29 Mar 2019 09:01:27 +0000 (UTC) Subject: Re: [PATCH 0/4] mm,memory_hotplug: allocate memmap from hotadded memory From: David Hildenbrand To: Oscar Salvador Cc: akpm@linux-foundation.org, mhocko@suse.com, dan.j.williams@intel.com, Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20190328134320.13232-1-osalvador@suse.de> <20190329084547.5k37xjwvkgffwajo@d104.suse.de> <23dcfb4a-339b-dcaf-c037-331f82fdef5a@redhat.com> Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <23dcfb4a-339b-dcaf-c037-331f82fdef5a@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Fri, 29 Mar 2019 09:01:30 +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 29.03.19 09:56, David Hildenbrand wrote: > On 29.03.19 09:45, Oscar Salvador wrote: >> On Thu, Mar 28, 2019 at 04:31:44PM +0100, David Hildenbrand wrote: >>> Correct me if I am wrong. I think I was confused - vmemmap data is still >>> allocated *per memory block*, not for the whole added memory, correct? >> >> No, vmemap data is allocated per memory-resource added. >> In case a DIMM, would be a DIMM, in case a qemu memory-device, would be that >> memory-device. >> That is counting that ACPI does not split the DIMM/memory-device in several memory >> resources. >> If that happens, then acpi_memory_enable_device() calls __add_memory for every >> memory-resource, which means that the vmemmap data will be allocated per >> memory-resource. >> I did not see this happening though, and I am not sure under which circumstances >> can happen (I have to study the ACPI code a bit more). >> >> The problem with allocating vmemmap data per memblock, is the fragmentation. >> Let us say you do the following: >> >> * memblock granularity 128M >> >> (qemu) object_add memory-backend-ram,id=ram0,size=256M >> (qemu) device_add pc-dimm,id=dimm0,memdev=ram0,node=1 >> >> This will create two memblocks (2 sections), and if we allocate the vmemmap >> data for each corresponding section within it section(memblock), you only get >> 126M contiguous memory. > > Oh okay, so actually the way I guessed it would be now. > > While this makes totally sense, I'll have to look how it is currently > handled, meaning if there is a change. I somewhat remembering that > delayed struct pages initialization would initialize vmmap per section, > not per memory resource. > > But as I work on 10 things differently, my mind sometimes seems to > forget stuff in order to replace it with random nonsense. Will look into > the details to not have to ask too many dumb questions. s/differently/concurrently/ See, nonsense ;) -- Thanks, David / dhildenb