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=-8.0 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,URIBL_BLOCKED, 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 85FE8C4338F for ; Mon, 9 Aug 2021 07:41:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 60D1D60FC2 for ; Mon, 9 Aug 2021 07:41:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233522AbhHIHmG (ORCPT ); Mon, 9 Aug 2021 03:42:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:59732 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233467AbhHIHmB (ORCPT ); Mon, 9 Aug 2021 03:42:01 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628494900; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EKDuFOXcudRR7I95TUwGAE5VyDFCMtB+gvkbBiNEmAE=; b=WJhSspK6qpPJArjXVec1o/hiQhR6anLKI/6v966QT6vHvtj0mfKx+cxYBVyYaaS/edi+47 6Yjh2MTdsaO0kj872q4KI2uLM/73i4xdk038QUvX9sFPFq6c3pWbyNPp0X5z1Z6W4jIHMg anhtMAeGmLls0rpiXR+ByrG5lxQel1w= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-374-byWFYvCAMVyewqATwbWLDw-1; Mon, 09 Aug 2021 03:41:38 -0400 X-MC-Unique: byWFYvCAMVyewqATwbWLDw-1 Received: by mail-wm1-f71.google.com with SMTP id o26-20020a05600c511ab0290252d0248251so4326954wms.1 for ; Mon, 09 Aug 2021 00:41:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:organization:subject :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=EKDuFOXcudRR7I95TUwGAE5VyDFCMtB+gvkbBiNEmAE=; b=JesS22p67taahBCE2xRh5tEMerU0tKy4aIB5Y9wLmXIP7biu2WVyR9m4ynVbcn+43w cSFx/2UgUddDWkDayBbg5Rj0TG87UKeBAY55CNi3W+kihuqGucl/5kxOdGIcB9GPSO94 s9CbNtWbBKVsZ1puUv6T6pK+8cnT9VywIwfg6TTqy4w4RDPRMYZqxJD7CqFd/G0UHLLk raiOsGvNax3NIpeh86YaQ/dvEpwFGQ2pUJP40BpUtPc9+p6mhU8z7CNhCazziEE7bhE2 +cdoRr7jHhnnvfXaoS+B3z+lMxFXqZacRO4g5nxWUJgr2gWAO5vyrLPqEZ1HWUTGerFx 3x/g== X-Gm-Message-State: AOAM530Km4ZkwfSvZAzX4w/PiJRfRxOfEpboZA71Svp+9OGQG8tvStFg MPCIe4dOJlXdJhpeqL6jN/T58uIolbaxbH/vo4Ka0ZIwOBqJV3VagxMNyydzxPGKJYI/LiIuxmr YNu19fwBZrW3DId7R/T7WmKF5rtbi/XGDppFAgsb0Ki8qtPsbhqDyW67SnCVfzu/a4gzYTfFA X-Received: by 2002:a05:600c:2248:: with SMTP id a8mr10951232wmm.80.1628494896864; Mon, 09 Aug 2021 00:41:36 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxBjfqegUXUj0G3xjeCjq++n5NBqn1S/Z5VUnLcosVs95+fyJXmZVKh5wXsx6d1EodG9WjJuA== X-Received: by 2002:a05:600c:2248:: with SMTP id a8mr10951214wmm.80.1628494896660; Mon, 09 Aug 2021 00:41:36 -0700 (PDT) Received: from ?IPv6:2003:d8:2f0a:7f00:fad7:3bc9:69d:31f? (p200300d82f0a7f00fad73bc9069d031f.dip0.t-ipconnect.de. [2003:d8:2f0a:7f00:fad7:3bc9:69d:31f]) by smtp.gmail.com with ESMTPSA id c190sm16925787wma.21.2021.08.09.00.41.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Aug 2021 00:41:36 -0700 (PDT) To: Zi Yan , linux-mm@kvack.org Cc: Matthew Wilcox , Vlastimil Babka , "Kirill A . Shutemov" , Mike Kravetz , Michal Hocko , John Hubbard , linux-kernel@vger.kernel.org References: <20210805190253.2795604-1-zi.yan@sent.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot time parameter. Message-ID: <28b57903-fae6-47ac-7e1b-a1dd41421349@redhat.com> Date: Mon, 9 Aug 2021 09:41:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210805190253.2795604-1-zi.yan@sent.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.08.21 21:02, Zi Yan wrote: > From: Zi Yan > > Hi all, > > This patchset add support for kernel boot time adjustable MAX_ORDER, so that > user can change the largest size of pages obtained from buddy allocator. It also > removes the restriction on MAX_ORDER based on SECTION_SIZE_BITS, so that > buddy allocator can merge PFNs across memory sections when SPARSEMEM_VMEMMAP is > set. It is on top of v5.14-rc4-mmotm-2021-08-02-18-51. > > Motivation > === > > This enables kernel to allocate 1GB pages and is necessary for my ongoing work > on adding support for 1GB PUD THP[1]. This is also the conclusion I came up with > after some discussion with David Hildenbrand on what methods should be used for > allocating gigantic pages[2], since other approaches like using CMA allocator or > alloc_contig_pages() are regarded as suboptimal. > > This also prevents increasing SECTION_SIZE_BITS when increasing MAX_ORDER, since > increasing SECTION_SIZE_BITS is not desirable as memory hotadd/hotremove chunk > size will be increased as well, causing memory management difficulty for VMs. > > In addition, make MAX_ORDER a kernel boot time parameter can enable user to > adjust buddy allocator without recompiling the kernel for their own needs, so > that one can still have a small MAX_ORDER if he/she does not need to allocate > gigantic pages like 1GB PUD THPs. > > Background > === > > At the moment, kernel imposes MAX_ORDER - 1 + PAGE_SHFIT < SECTION_SIZE_BITS > restriction. This prevents buddy allocator merging pages across memory sections, > as PFNs might not be contiguous and code like page++ would fail. But this would > not be an issue when SPARSEMEM_VMEMMAP is set, since all struct page are > virtually contiguous. In addition, as long as buddy allocator checks the PFN > validity during buddy page merging (done in Patch 3), pages allocated from > buddy allocator can be manipulated by code like page++. > > > Description > === > > I tested the patchset on both x86_64 and ARM64 at 4KB, 16KB, and 64KB base > pages. The systems boot and ltp mm test suite finished without issue. Also > memory hotplug worked on x86_64 when I tested. It definitely needs more tests > and reviews for other architectures. > > In terms of the concerns on performance degradation if MAX_ORDER is increased, > I did some initial performance tests comparing MAX_ORDER=11 and MAX_ORDER=20 on > x86_64 machines and saw no performance difference[3]. > > Patch 1 excludes MAX_ORDER check from 32bit vdso compilation. The check uses > irrelevant 32bit SECTION_SIZE_BITS during 64bit kernel compilation. The > exclusion does not break the check in 32bit kernel, since the check will still > be performed during other kernel component compilation. > > Patch 2 gives FORCE_MAX_ZONEORDER a better name. > > Patch 3 restores the pfn_valid_within() check when buddy allocator can merge > pages across memory sections. The check was removed when ARM64 gets rid of holes > in zones, but holes can appear in zones again after this patchset. > > Patch 4-11 convert the use of MAX_ORDER to SECTION_SIZE_BITS or its derivative > constants, since these code places use MAX_ORDER as boundary check for > physically contiguous pages, where SECTION_SIZE_BITS should be used. After this > patchset, MAX_ORDER can go beyond SECTION_SIZE_BITS, the code can break. > I separate changes to different patches for easy review and can merge them into > a single one if that works better. > > Patch 12 adds a new Kconfig option SET_MAX_ORDER to allow specifying MAX_ORDER > when ARCH_FORCE_MAX_ORDER is not used by the arch, like x86_64. > > Patch 13 converts statically allocated arrays with MAX_ORDER length to dynamic > ones if possible and prepares for making MAX_ORDER a boot time parameter. > > Patch 14 adds a new MIN_MAX_ORDER constant to replace soon-to-be-dynamic > MAX_ORDER for places where converting static array to dynamic one is causing > hassle and not necessary, i.e., ARM64 hypervisor page allocation and SLAB. > > Patch 15 finally changes MAX_ORDER to be a kernel boot time parameter. > > > Any suggestion and/or comment is welcome. Thanks. > > > TODO > === > > 1. Redo the performance comparison tests using this patchset to understand the > performance implication of changing MAX_ORDER. 2. Make alloc_contig_range() cleanly deal with pageblock_order instead of MAX_ORDER - 1 to not force the minimal CMA area size/alignment to be e.g., 1 GiB instead of 4 MiB and to keep virtio-mem working as expected. virtio-mem short term would mean disallowing initialization when an incompatible setup (MAX_ORDER_NR_PAGE > SECTION_NR_PAGES) is detected and bailing out loud that the admin has to fix that on the command line. I have optimizing alloc_contig_range() on my todo list, to get rid of the MAX_ORDER -1 dependency in virtio-mem; but I have no idea when I'll have time to work on that. -- Thanks, David / dhildenb