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=-8.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,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 345FDC433E2 for ; Thu, 10 Sep 2020 08:09:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA8D720731 for ; Thu, 10 Sep 2020 08:09:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Uctz+8i0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730150AbgIJIJL (ORCPT ); Thu, 10 Sep 2020 04:09:11 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:54033 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726381AbgIJIJF (ORCPT ); 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Thu, 10 Sep 2020 08:08:59 +0000 (UTC) Received: from [10.36.113.88] (ovpn-113-88.ams2.redhat.com [10.36.113.88]) by smtp.corp.redhat.com (Postfix) with ESMTP id A1A57702E7; Thu, 10 Sep 2020 08:08:57 +0000 (UTC) Subject: Re: [PATCH] arm64/mm: add fallback option to allocate virtually contiguous memory To: Anshuman Khandual , Sudarshan Rajagopalan , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Catalin Marinas , Will Deacon , Mark Rutland , Logan Gunthorpe , Andrew Morton , Steven Price References: <01010174769e2b68-a6f3768e-aef8-43c7-b357-a8cb1e17d3eb-000000@us-west-2.amazonses.com> <0475e813-cb95-0992-39e4-593bfd5cdbf8@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63W5Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAjwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat GmbH Message-ID: <372df305-3bff-bf8e-e2a3-a03932df58d5@redhat.com> Date: Thu, 10 Sep 2020 10:08:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <0475e813-cb95-0992-39e4-593bfd5cdbf8@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10.09.20 08:45, Anshuman Khandual wrote: > Hello Sudarshan, > > On 09/10/2020 11:35 AM, Sudarshan Rajagopalan wrote: >> When section mappings are enabled, we allocate vmemmap pages from physically >> continuous memory of size PMD_SZIE using vmemmap_alloc_block_buf(). Section> mappings are good to reduce TLB pressure. But when system is highly fragmented >> and memory blocks are being hot-added at runtime, its possible that such >> physically continuous memory allocations can fail. Rather than failing the > > Did you really see this happen on a system ? > >> memory hot-add procedure, add a fallback option to allocate vmemmap pages from >> discontinuous pages using vmemmap_populate_basepages(). > > Which could lead to a mixed page size mapping in the VMEMMAP area. Right, with gives you a slight performance hit - nobody really cares, especially if it happens in corner cases only. At least x86_64 (see vmemmap_populate_hugepages()) and s390x (added recently by me) implement that behavior. Assume you run in a virtualized environment where your hypervisor tries to do some smart dynamic guest resizing - like monitoring the guest memory consumption and adding more memory on demand. You much rather want hotadd to succeed (in these corner cases) that failing just because you weren't able to grab a huge page in one instance. Examples include XEN balloon, Hyper-V balloon, and virtio-mem. We might see some of these for arm64 as well (if don't already do). > Allocation failure in vmemmap_populate() should just cleanly fail > the memory hot add operation, which can then be retried. Why the > retry has to be offloaded to kernel ? (not sure what "offloaded to kernel" really means here - add_memory() is also just triggered from the kernel) I disagree, we should try our best to add memory and make it available, especially when short on memory already. -- Thanks, David / dhildenb 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=-8.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 A1B2FC43461 for ; Thu, 10 Sep 2020 08:10:29 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 41A4A20731 for ; 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bh=MWe5lAa1TnJBDk3hGPO0meJcDbYEKLd27dPFAHQzo0Q=; b=Ip43FBA+rKiKjn6hIN9YO7Np+ROPF3SO9oL6BxLwRyJXMPXZ0hh26lD1e1gZDgMQDTXJvH p5LL7ktRarbTzOtd4ioFCiO9PVhwEbEHdf+Eykg5xmzC0lauddw+dQX3IWkTHacSqORyDn flUq/If3TZ8cfPvmcz+EMpUKjDkkiTU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-504-aL7eg-OIM9uf5CSKIx3sDQ-1; Thu, 10 Sep 2020 04:09:01 -0400 X-MC-Unique: aL7eg-OIM9uf5CSKIx3sDQ-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id D4EA81882FAA; Thu, 10 Sep 2020 08:08:59 +0000 (UTC) Received: from [10.36.113.88] (ovpn-113-88.ams2.redhat.com [10.36.113.88]) by smtp.corp.redhat.com (Postfix) with ESMTP id A1A57702E7; Thu, 10 Sep 2020 08:08:57 +0000 (UTC) Subject: Re: [PATCH] arm64/mm: add fallback option to allocate virtually contiguous memory To: Anshuman Khandual , Sudarshan Rajagopalan , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <01010174769e2b68-a6f3768e-aef8-43c7-b357-a8cb1e17d3eb-000000@us-west-2.amazonses.com> <0475e813-cb95-0992-39e4-593bfd5cdbf8@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <0475e813-cb95-0992-39e4-593bfd5cdbf8@arm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200910_040905_744950_22605318 X-CRM114-Status: GOOD ( 20.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Will Deacon , Catalin Marinas , Steven Price , Andrew Morton , Logan Gunthorpe Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 10.09.20 08:45, Anshuman Khandual wrote: > Hello Sudarshan, > > On 09/10/2020 11:35 AM, Sudarshan Rajagopalan wrote: >> When section mappings are enabled, we allocate vmemmap pages from physically >> continuous memory of size PMD_SZIE using vmemmap_alloc_block_buf(). Section> mappings are good to reduce TLB pressure. But when system is highly fragmented >> and memory blocks are being hot-added at runtime, its possible that such >> physically continuous memory allocations can fail. Rather than failing the > > Did you really see this happen on a system ? > >> memory hot-add procedure, add a fallback option to allocate vmemmap pages from >> discontinuous pages using vmemmap_populate_basepages(). > > Which could lead to a mixed page size mapping in the VMEMMAP area. Right, with gives you a slight performance hit - nobody really cares, especially if it happens in corner cases only. At least x86_64 (see vmemmap_populate_hugepages()) and s390x (added recently by me) implement that behavior. Assume you run in a virtualized environment where your hypervisor tries to do some smart dynamic guest resizing - like monitoring the guest memory consumption and adding more memory on demand. You much rather want hotadd to succeed (in these corner cases) that failing just because you weren't able to grab a huge page in one instance. Examples include XEN balloon, Hyper-V balloon, and virtio-mem. We might see some of these for arm64 as well (if don't already do). > Allocation failure in vmemmap_populate() should just cleanly fail > the memory hot add operation, which can then be retried. Why the > retry has to be offloaded to kernel ? (not sure what "offloaded to kernel" really means here - add_memory() is also just triggered from the kernel) I disagree, we should try our best to add memory and make it available, especially when short on memory already. -- Thanks, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel