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=-11.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 B0C95C4167B for ; Thu, 10 Dec 2020 03:58:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7BF3223BA7 for ; Thu, 10 Dec 2020 03:58:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731926AbgLJD6V (ORCPT ); Wed, 9 Dec 2020 22:58:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48224 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731797AbgLJD6C (ORCPT ); Wed, 9 Dec 2020 22:58:02 -0500 Received: from mail-pf1-x443.google.com (mail-pf1-x443.google.com [IPv6:2607:f8b0:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6BB22C0613D6 for ; Wed, 9 Dec 2020 19:57:22 -0800 (PST) Received: by mail-pf1-x443.google.com with SMTP id w6so2798897pfu.1 for ; Wed, 09 Dec 2020 19:57:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=Re97coN1efwIJ9Nx54jKVBSk5iC93sAGDNFz2ZhGMIw=; b=xqUbN1q1BLimYnYGtzvEat1ykwv6ZsS74hV1PPYkuLKLzGj0bVnJI1yHTco5PrzKgz Sw8VM1p0JaxnCEuA13eElkVoRfkZ9wilho3acYxE1UsR++jH7fkndJEo8GkSM/Hxwtc/ rjQCiu5XA9GP/kxCFDIvZy9X6P4c9hol1N5ISMZddh4HBZGkmoMYCTtFeMdb79pZycMN 40jdcLp3trPI02TaFi2w7ITIR5uveX9r+EWDVyRAF/M32d3HH6r9cSNkyLimu7kXOQl/ 7OcDQles76gmUPs39bcwqaARfxrnL+JXLP5K0jaQAylBpmP7QoEKqZEzYbzZ6tOQr+9Q kZLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=Re97coN1efwIJ9Nx54jKVBSk5iC93sAGDNFz2ZhGMIw=; b=UN17k358VsJ8L5sXQfiykOYDojN+iJagvfWbr/3WTarGT2bjwnWAPPltxiy0CXkjKP 48rXDk2HTsK8lMuhZpmFAcXy1Ji3h/ES2DBwahfif5igdkdLS2V1IdWfNT/t6mWkI0XP 4hw4N202PAn7WPMfV9G2rCug+NornxMZN298SB6y3yf7ihi1NXefygAuXexrcRVX9X9T xrGuN15e56iqvr2FP9EtOboOwaC2gtKk7E4+mPr8AqkUXww+7FilH754tGRNQvhollzm tkUvTwk2rynRtNkPzVwDMyCU5ZvUHDx3Liu3Z8LmYsZccyVdcskVbytLsap2zJOQtWZn jcwA== X-Gm-Message-State: AOAM531SebtmcgwA95bWx19HGLRBqeS4/0jUYkVL18vaMW8YHtFhoKup Lbu4m+yIcV2ADpNb40QKyS6Aqw== X-Google-Smtp-Source: ABdhPJyrppp6bKAjkC37jc/EfXs2UPF2Wwx2E32Z+qRSxrIGtRy8uVwRb4JRckCAKRDX24xi5x6z7A== X-Received: by 2002:a62:1409:0:b029:19e:14d1:efb0 with SMTP id 9-20020a6214090000b029019e14d1efb0mr5055596pfu.14.1607572641740; Wed, 09 Dec 2020 19:57:21 -0800 (PST) Received: from localhost.localdomain ([103.136.220.85]) by smtp.gmail.com with ESMTPSA id f33sm4266535pgl.83.2020.12.09.19.57.11 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Dec 2020 19:57:21 -0800 (PST) From: Muchun Song To: corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, rdunlap@infradead.org, oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, almasrymina@google.com, rientjes@google.com, willy@infradead.org, osalvador@suse.de, mhocko@suse.com, song.bao.hua@hisilicon.com, david@redhat.com Cc: duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Muchun Song Subject: [PATCH v8 00/12] Free some vmemmap pages of HugeTLB page Date: Thu, 10 Dec 2020 11:55:14 +0800 Message-Id: <20201210035526.38938-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, This patch series will free some vmemmap pages(struct page structures) associated with each hugetlbpage when preallocated to save memory. In order to reduce the difficulty of the first version of code review. >From this version, we disable PMD/huge page mapping of vmemmap if this feature was enabled. This accutualy eliminate a bunch of the complex code doing page table manipulation. When this patch series is solid, we cam add the code of vmemmap page table manipulation in the future. The struct page structures (page structs) are used to describe a physical page frame. By default, there is a one-to-one mapping from a page frame to it's corresponding page struct. The HugeTLB pages consist of multiple base page size pages and is supported by many architectures. See hugetlbpage.rst in the Documentation directory for more details. On the x86 architecture, HugeTLB pages of size 2MB and 1GB are currently supported. Since the base page size on x86 is 4KB, a 2MB HugeTLB page consists of 512 base pages and a 1GB HugeTLB page consists of 4096 base pages. For each base page, there is a corresponding page struct. Within the HugeTLB subsystem, only the first 4 page structs are used to contain unique information about a HugeTLB page. HUGETLB_CGROUP_MIN_ORDER provides this upper limit. The only 'useful' information in the remaining page structs is the compound_head field, and this field is the same for all tail pages. By removing redundant page structs for HugeTLB pages, memory can returned to the buddy allocator for other uses. When the system boot up, every 2M HugeTLB has 512 struct page structs which size is 8 pages(sizeof(struct page) * 512 / PAGE_SIZE). HugeTLB struct pages(8 pages) page frame(8 pages) +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+ | | | 0 | -------------> | 0 | | | +-----------+ +-----------+ | | | 1 | -------------> | 1 | | | +-----------+ +-----------+ | | | 2 | -------------> | 2 | | | +-----------+ +-----------+ | | | 3 | -------------> | 3 | | | +-----------+ +-----------+ | | | 4 | -------------> | 4 | | 2MB | +-----------+ +-----------+ | | | 5 | -------------> | 5 | | | +-----------+ +-----------+ | | | 6 | -------------> | 6 | | | +-----------+ +-----------+ | | | 7 | -------------> | 7 | | | +-----------+ +-----------+ | | | | | | +-----------+ The value of page->compound_head is the same for all tail pages. The first page of page structs (page 0) associated with the HugeTLB page contains the 4 page structs necessary to describe the HugeTLB. The only use of the remaining pages of page structs (page 1 to page 7) is to point to page->compound_head. Therefore, we can remap pages 2 to 7 to page 1. Only 2 pages of page structs will be used for each HugeTLB page. This will allow us to free the remaining 6 pages to the buddy allocator. Here is how things look after remapping. HugeTLB struct pages(8 pages) page frame(8 pages) +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+ | | | 0 | -------------> | 0 | | | +-----------+ +-----------+ | | | 1 | -------------> | 1 | | | +-----------+ +-----------+ | | | 2 | ----------------^ ^ ^ ^ ^ ^ | | +-----------+ | | | | | | | | 3 | ------------------+ | | | | | | +-----------+ | | | | | | | 4 | --------------------+ | | | | 2MB | +-----------+ | | | | | | 5 | ----------------------+ | | | | +-----------+ | | | | | 6 | ------------------------+ | | | +-----------+ | | | | 7 | --------------------------+ | | +-----------+ | | | | | | +-----------+ When a HugeTLB is freed to the buddy system, we should allocate 6 pages for vmemmap pages and restore the previous mapping relationship. Apart from 2MB HugeTLB page, we also have 1GB HugeTLB page. It is similar to the 2MB HugeTLB page. We also can use this approach to free the vmemmap pages. In this case, for the 1GB HugeTLB page, we can save 4088 pages(There are 4096 pages for struct page structs, we reserve 2 pages for vmemmap and 8 pages for page tables. So we can save 4088 pages). This is a very substantial gain. On our server, run some SPDK/QEMU applications which will use 1024GB hugetlbpage. With this feature enabled, we can save ~16GB(1G hugepage)/~11GB (2MB hugepage, the worst case is 10GB while the best is 12GB) memory. Because there are vmemmap page tables reconstruction on the freeing/allocating path, it increases some overhead. Here are some overhead analysis. 1) Allocating 10240 2MB hugetlb pages. a) With this patch series applied: # time echo 10240 > /proc/sys/vm/nr_hugepages real 0m0.166s user 0m0.000s sys 0m0.166s # bpftrace -e 'kprobe:alloc_fresh_huge_page { @start[tid] = nsecs; } kretprobe:alloc_fresh_huge_page /@start[tid]/ { @latency = hist(nsecs - @start[tid]); delete(@start[tid]); }' Attaching 2 probes... @latency: [8K, 16K) 8360 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| [16K, 32K) 1868 |@@@@@@@@@@@ | [32K, 64K) 10 | | [64K, 128K) 2 | | b) Without this patch series: # time echo 10240 > /proc/sys/vm/nr_hugepages real 0m0.066s user 0m0.000s sys 0m0.066s # bpftrace -e 'kprobe:alloc_fresh_huge_page { @start[tid] = nsecs; } kretprobe:alloc_fresh_huge_page /@start[tid]/ { @latency = hist(nsecs - @start[tid]); delete(@start[tid]); }' Attaching 2 probes... @latency: [4K, 8K) 10176 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| [8K, 16K) 62 | | [16K, 32K) 2 | | Summarize: this feature is about ~2x slower than before. 2) Freeing 10240 2MB hugetlb pages. a) With this patch series applied: # time echo 0 > /proc/sys/vm/nr_hugepages real 0m0.004s user 0m0.000s sys 0m0.002s # bpftrace -e 'kprobe:__free_hugepage { @start[tid] = nsecs; } kretprobe:__free_hugepage /@start[tid]/ { @latency = hist(nsecs - @start[tid]); delete(@start[tid]); }' Attaching 2 probes... @latency: [16K, 32K) 10240 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| b) Without this patch series: # time echo 0 > /proc/sys/vm/nr_hugepages real 0m0.077s user 0m0.001s sys 0m0.075s # bpftrace -e 'kprobe:__free_hugepage { @start[tid] = nsecs; } kretprobe:__free_hugepage /@start[tid]/ { @latency = hist(nsecs - @start[tid]); delete(@start[tid]); }' Attaching 2 probes... @latency: [4K, 8K) 9950 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| [8K, 16K) 287 |@ | [16K, 32K) 3 | | Summarize: The overhead of __free_hugepage is about ~2-4x slower than before. But according to the allocation test above, I think that here is also ~2x slower than before. But why the 'real' time of patched is smaller than before? Because In this patch series, the freeing hugetlb is asynchronous(through kwoker). Although the overhead has increased, the overhead is not significant. Like Mike said, "However, remember that the majority of use cases create hugetlb pages at or shortly after boot time and add them to the pool. So, additional overhead is at pool creation time. There is no change to 'normal run time' operations of getting a page from or returning a page to the pool (think page fault/unmap)". Todo: - Free all of the tail vmemmap pages Now for the 2MB HugrTLB page, we only free 6 vmemmap pages. we really can free 7 vmemmap pages. In this case, we can see 8 of the 512 struct page structures has beed set PG_head flag. If we can adjust compound_head() slightly and make compound_head() return the real head struct page when the parameter is the tail struct page but with PG_head flag set. In order to make the code evolution route clearer. This feature can can be a separate patch after this patchset is solid. - Support for other architectures (e.g. aarch64). - Enable PMD/huge page mapping of vmemmap even if this feature was enabled. Changelog in v7 -> v8: - Adjust the order of patches. Very thanks to David and Oscar. Your suggestions are very valuable. Changelog in v6 -> v7: - Rebase to linux-next 20201130 - Do not use basepage mapping for vmemmap when this feature is disabled. - Rework some patchs. [PATCH v6 08/16] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page [PATCH v6 10/16] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page Thanks to Oscar and Barry. Changelog in v5 -> v6: - Disable PMD/huge page mapping of vmemmap if this feature was enabled. - Simplify the first version code. Changelog in v4 -> v5: - Rework somme comments and code in the [PATCH v4 04/21] and [PATCH v4 05/21]. Thanks to Mike and Oscar's suggestions. Changelog in v3 -> v4: - Move all the vmemmap functions to hugetlb_vmemmap.c. - Make the CONFIG_HUGETLB_PAGE_FREE_VMEMMAP default to y, if we want to disable this feature, we should disable it by a boot/kernel command line. - Remove vmemmap_pgtable_{init, deposit, withdraw}() helper functions. - Initialize page table lock for vmemmap through core_initcall mechanism. Thanks for Mike and Oscar's suggestions. Changelog in v2 -> v3: - Rename some helps function name. Thanks Mike. - Rework some code. Thanks Mike and Oscar. - Remap the tail vmemmap page with PAGE_KERNEL_RO instead of PAGE_KERNEL. Thanks Matthew. - Add some overhead analysis in the cover letter. - Use vmemap pmd table lock instead of a hugetlb specific global lock. Changelog in v1 -> v2: - Fix do not call dissolve_compound_page in alloc_huge_page_vmemmap(). - Fix some typo and code style problems. - Remove unused handle_vmemmap_fault(). - Merge some commits to one commit suggested by Mike. Muchun Song (12): mm/memory_hotplug: Factor out bootmem core functions to bootmem_info.c mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP mm/bootmem_info: Introduce free_bootmem_page helper mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page mm/hugetlb: Defer freeing of HugeTLB pages mm/hugetlb: Allocate the vmemmap pages associated with each HugeTLB page mm/hugetlb: Set the PageHWPoison to the raw error page mm/hugetlb: Flush work when dissolving hugetlb page mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate mm/hugetlb: Gather discrete indexes of tail page mm/hugetlb: Optimize the code with the help of the compiler Documentation/admin-guide/kernel-parameters.txt | 9 + Documentation/admin-guide/mm/hugetlbpage.rst | 3 + arch/x86/mm/init_64.c | 13 +- fs/Kconfig | 15 + include/linux/bootmem_info.h | 59 +++ include/linux/hugetlb.h | 36 ++ include/linux/hugetlb_cgroup.h | 15 +- include/linux/memory_hotplug.h | 27 -- mm/Makefile | 2 + mm/bootmem_info.c | 124 +++++++ mm/hugetlb.c | 165 +++++++-- mm/hugetlb_vmemmap.c | 463 ++++++++++++++++++++++++ mm/hugetlb_vmemmap.h | 44 +++ mm/memory_hotplug.c | 116 ------ mm/sparse.c | 1 + 15 files changed, 918 insertions(+), 174 deletions(-) create mode 100644 include/linux/bootmem_info.h create mode 100644 mm/bootmem_info.c create mode 100644 mm/hugetlb_vmemmap.c create mode 100644 mm/hugetlb_vmemmap.h -- 2.11.0