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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 3091EC433FF for ; Thu, 1 Aug 2019 18:46:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 017B12084C for ; Thu, 1 Aug 2019 18:46:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730133AbfHASqJ (ORCPT ); Thu, 1 Aug 2019 14:46:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57050 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726017AbfHASqI (ORCPT ); Thu, 1 Aug 2019 14:46:08 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9ACBF30D0F62; Thu, 1 Aug 2019 18:46:07 +0000 (UTC) Received: from [10.36.116.65] (ovpn-116-65.ams2.redhat.com [10.36.116.65]) by smtp.corp.redhat.com (Postfix) with ESMTP id D2A085C541; Thu, 1 Aug 2019 18:46:04 +0000 (UTC) Subject: Re: [PATCH v3 0/5] Allocate memmap from hotadded memory To: Oscar Salvador , akpm@linux-foundation.org Cc: dan.j.williams@intel.com, pasha.tatashin@soleen.com, mhocko@suse.com, anshuman.khandual@arm.com, Jonathan.Cameron@huawei.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190725160207.19579-1-osalvador@suse.de> 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: <777bd999-5c76-bd43-9f46-a827423798ce@redhat.com> Date: Thu, 1 Aug 2019 20:46:04 +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: <20190725160207.19579-1-osalvador@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Thu, 01 Aug 2019 18:46:07 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.07.19 18:02, Oscar Salvador wrote: > Here we go with v3. > > v3 -> v2: > * Rewrite about vmemmap pages handling. > Prior to this version, I was (ab)using hugepages fields > from struct page, while here I am officially adding a new > sub-page type with the fields I need. > > * Drop MHP_MEMMAP_{MEMBLOCK,DEVICE} in favor of MHP_MEMMAP_ON_MEMORY. > While I am still not 100% if this the right decision, and while I > still see some gaining in having MHP_MEMMAP_{MEMBLOCK,DEVICE}, > having only one flag ease the code. > If the user wants to allocate memmaps per memblock, it'll > have to call add_memory() variants with memory-block granularity. > > If we happen to have a more clear usecase MHP_MEMMAP_MEMBLOCK > flag in the future, so user does not have to bother about the way > it calls add_memory() variants, but only pass a flag, we can add it. > Actually, I already had the code, so add it in the future is going to be > easy. > > * Granularity check when hot-removing memory. > Just checking that the granularity is the same. > > [Testing] > > - x86_64: small and large memblocks (128MB, 1G and 2G) > > So far, only acpi memory hotplug uses the new flag. > The other callers can be changed depending on their needs. > > [Coverletter] > > This is another step to make memory hotplug more usable. The primary > goal of this patchset is to reduce memory overhead of the hot-added > memory (at least for SPARSEMEM_VMEMMAP memory model). The current way we use > to populate memmap (struct page array) has two main drawbacks: > > a) it consumes an additional memory until the hotadded memory itself is > onlined and > b) memmap might end up on a different numa node which is especially true > for movable_node configuration. > > a) it is a problem especially for memory hotplug based memory "ballooning" > solutions when the delay between physical memory hotplug and the > onlining can lead to OOM and that led to introduction of hacks like auto > onlining (see 31bc3858ea3e ("memory-hotplug: add automatic onlining > policy for the newly added memory")). > > b) can have performance drawbacks. > > One way to mitigate all these issues is to simply allocate memmap array > (which is the largest memory footprint of the physical memory hotplug) > from the hot-added memory itself. SPARSEMEM_VMEMMAP memory model allows > us to map any pfn range so the memory doesn't need to be online to be > usable for the array. See patch 3 for more details. > This feature is only usable when CONFIG_SPARSEMEM_VMEMMAP is set. > > [Overall design]: > > Implementation wise we reuse vmem_altmap infrastructure to override > the default allocator used by vmemap_populate. Once the memmap is > allocated we need a way to mark altmap pfns used for the allocation. > If MHP_MEMMAP_ON_MEMORY flag was passed, we set up the layout of the > altmap structure at the beginning of __add_pages(), and then we call > mark_vmemmap_pages(). > > MHP_MEMMAP_ON_MEMORY flag parameter will specify to allocate memmaps > from the hot-added range. > If callers wants memmaps to be allocated per memory block, it will > have to call add_memory() variants in memory-block granularity > spanning the whole range, while if it wants to allocate memmaps > per whole memory range, just one call will do. > > Want to add 384MB (3 sections, 3 memory-blocks) > e.g: > > add_memory(0x1000, size_memory_block); > add_memory(0x2000, size_memory_block); > add_memory(0x3000, size_memory_block); > Some more thoughts: 1. It can happen that pfn_online() for a vmemmap page returns either true or false, depending on the state of the section. It could be that the memory block holding the vmemmap is offline while another memory block making use of it is online. I guess this isn't bad (I assume it is similar for the altmap), however it could be that makedumpfile will exclude the vmemmap from dumps (as it will usually only dump pages in sections marked online if I am not wrong - maybe it special cases vmemmaps already). Also, could be that it is not saved/restored during hibernation. We'll have to verify. 2. memmap access when adding/removing memory The memmap is initialized when onlining memory. We still have to clean up accessing the memmap in remove_memory(). You seem to introduce new users - which is bad. Especially when removing memory we never onlined. When removing memory, you shouldn't have to worry about any orders - nobody should touch the memmap. I am aware that we still query the zone - are there other users that touch the memmap when removing memory? 3. isolation/compaction I am not sure if simply unconditionally skipping over Vmemmap pages is a good idea. I would have guessed it is better to hinder callers from even triggering this. E.g., Only online the pieces that don't contain the vmemmap. When offlining a memory block, only actually try to offline the pieces that were onlined - excluding the vmemmap. Might require some smaller reworks but shouldn't be too hard as far as I can tell. 4. mhp_flags and altmap with __add_pages() I have hoped that we can handle the specific of MMAP_ON_MEMORY completely in add_memory() - nobody else needs MMAP_ON_MEMORY (we have the generic altmap concept already). So, setup the struct vmem_altmap; in add_memory() and pass it directly. During arch_add_memory(), nobody should be touching the vmemmap either way, as it is completely uninitialized. When we return from arch_add_memory() in add_memory(), we could then initialize the memmap for the vmemmap pages (e.g., set them to PageVmemmap) - via mhp_mark_vmemmap_pages() or such. What exactly speaks against this approach? (moving the MMAP_ON_MEMORY handling completely out of __add_pages())? Am I missing some access the could be evil while the pages are not mapped? (I'd love to see __add_pages() only eat an altmap again, and keep the MMAP_ON_MEMORY thingy specific to add_memory()) -- Thanks, David / dhildenb