From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F252FC32751 for ; Wed, 31 Jul 2019 13:42:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B73FB206A2 for ; Wed, 31 Jul 2019 13:42:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729630AbfGaNm5 (ORCPT ); Wed, 31 Jul 2019 09:42:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59381 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726907AbfGaNm5 (ORCPT ); Wed, 31 Jul 2019 09:42:57 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 84E8C811DE; Wed, 31 Jul 2019 13:42:56 +0000 (UTC) Received: from [10.36.117.240] (ovpn-117-240.ams2.redhat.com [10.36.117.240]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9596E19C5B; Wed, 31 Jul 2019 13:42:54 +0000 (UTC) Subject: Re: [PATCH v1] drivers/base/memory.c: Don't store end_section_nr in memory blocks To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Greg Kroah-Hartman , "Rafael J. Wysocki" , Andrew Morton , Pavel Tatashin , Dan Williams , Oscar Salvador References: <20190731122213.13392-1-david@redhat.com> <20190731124356.GL9330@dhcp22.suse.cz> <20190731132534.GQ9330@dhcp22.suse.cz> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: <58bd9479-051b-a13b-b6d0-c93aac2ed1b3@redhat.com> Date: Wed, 31 Jul 2019 15:42:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190731132534.GQ9330@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 31 Jul 2019 13:42:56 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31.07.19 15:25, Michal Hocko wrote: > On Wed 31-07-19 15:12:12, David Hildenbrand wrote: >> On 31.07.19 14:43, Michal Hocko wrote: >>> On Wed 31-07-19 14:22:13, David Hildenbrand wrote: >>>> Each memory block spans the same amount of sections/pages/bytes. The size >>>> is determined before the first memory block is created. No need to store >>>> what we can easily calculate - and the calculations even look simpler now. >>> >>> While this cleanup helps a bit, I am not sure this is really worth >>> bothering. I guess we can agree when I say that the memblock interface >>> is suboptimal (to put it mildly). Shouldn't we strive for making it >>> a real hotplug API in the future? What do I mean by that? Why should >>> be any memblock fixed in size? Shouldn't we have use hotplugable units >>> instead (aka pfn range that userspace can work with sensibly)? Do we >>> know of any existing userspace that would depend on the current single >>> section res. 2GB sized memblocks? >> >> Short story: It is already ABI (e.g., >> /sys/devices/system/memory/block_size_bytes) - around since 2005 (!) - >> since we had memory block devices. >> >> I suspect that it is mainly manually used. But I might be wrong. > > Any pointer to the real userspace depending on it? Most usecases I am > aware of rely on udev events and either onlining or offlining the memory > in the handler. Yes, that's also what I know - onlining and triggering kexec(). On s390x, admins online sub-increments to selectively add memory to a VM - but we could still emulate that by adding memory for that use case in the kernel in the current granularity. See https://books.google.de/books?id=afq4CgAAQBAJ&pg=PA117&lpg=PA117&dq=/sys/devices/system/memory/block_size_bytes&source=bl&ots=iYk_vW5O4G&sig=ACfU3U0s-O-SOVaQO-7HpKO5Hj866w9Pxw&hl=de&sa=X&ved=2ahUKEwjOjPqIot_jAhVPfZoKHcxpAqcQ6AEwB3oECAgQAQ#v=onepage&q=%2Fsys%2Fdevices%2Fsystem%2Fmemory%2Fblock_size_bytes&f=false > > I know we have documented this as an ABI and it is really _sad_ that > this ABI didn't get through normal scrutiny any user visible interface > should go through but these are sins of the past... A quick google search indicates that Kata containers queries the block size: https://github.com/kata-containers/runtime/issues/796 Powerpc userspace queries it: https://groups.google.com/forum/#!msg/powerpc-utils-devel/dKjZCqpTxus/AwkstV2ABwAJ I can imagine that ppc dynamic memory onlines only pieces of added memory - DIMMs AFAIK (haven't looked at the details). There might be more users. > >> Long story: >> >> How would you want to number memory blocks? At least no longer by phys >> index. For now, memory blocks are ordered and numbered by their block id. > > memory_${mem_section_nr_of_start_pfn} > Fair enough, although this could break some scripts where people manually offline/online specific blocks. (but who knows what people/scripts do :( ) >> Admins might want to online parts of a DIMM MOVABLE/NORMAL, to more >> reliably use huge pages but still have enough space for kernel memory >> (e.g., page tables). They might like that a DIMM is actually a set of >> memory blocks instead of one big chunk. > > They might. Do they though? There are many theoretical usecases but > let's face it, there is a cost given to the current state. E.g. the > number of memblock directories is already quite large on machines with a > lot of memory even though they use large blocks. That has negative > implications already (e.g. the number of events you get, any iteration > on the /sys etc.). Also 2G memblocks are quite arbitrary and they > already limit the above usecase some, right? I mean there are other theoretical issues: Onlining a very big DIMM in one shot might trigger OOM, while slowly adding/onlining would currently works. Who knows if that is relevant in practice. Also, it would break the current use case of memtrace, which removes memory in a granularity that wasn't added. But luckily, memtrace is an exception :) > >> IOW: You can consider it a restriction to add e.g., DIMMs only in one >> bigger chunks. >> >>> >>> All that being said, I do not oppose to the patch but can we start >>> thinking about the underlying memblock limitations rather than micro >>> cleanups? >> >> I am pro cleaning up what we have right now, not expect it to eventually >> change some-when in the future. (btw, I highly doubt it will change) > > I do agree, but having the memblock fixed size doesn't really go along > with variable memblock size if we ever go there. But as I've said I am > not really against the patch. Fair enough, for now I am not convinced that we will actually see variable memory blocks in the near future. Thanks for the discussion (I was thinking about the same concept a while back when trying to find out if there could be an easy way to identify which memory blocks belong to a single DIMM you want to eventually unplug and therefore online it all to the MOVABLE zone). -- Thanks, David / dhildenb