From patchwork Tue Mar 8 23:47:23 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Yu Zhao X-Patchwork-Id: 12774491 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9417C433EF for ; Tue, 8 Mar 2022 23:48:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 623928D0010; Tue, 8 Mar 2022 18:48:44 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 583218D0001; Tue, 8 Mar 2022 18:48:44 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3D6988D0010; Tue, 8 Mar 2022 18:48:44 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.27]) by kanga.kvack.org (Postfix) with ESMTP id 2F6C08D0001 for ; Tue, 8 Mar 2022 18:48:44 -0500 (EST) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id D8F5F1ED5 for ; Tue, 8 Mar 2022 23:48:43 +0000 (UTC) X-FDA: 79222861326.06.59D0A5C Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) by imf16.hostedemail.com (Postfix) with ESMTP id 43AF6180007 for ; Tue, 8 Mar 2022 23:48:43 +0000 (UTC) Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-2dcd6a5e4b6so3955937b3.4 for ; Tue, 08 Mar 2022 15:48:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc:content-transfer-encoding; bh=5w1OIfygzSAzOtR1gEmt6DQmNATik/MV9LcnsLZ7twE=; b=VmtraZ998i0c3SLIXGsaDapNpLDnNwC90h3F9NhYwhfeLG4kWQ0pxVDK0xFqBdd31/ O75Uyb1YCFIXEs3jPi1jSsnrhN0sSNoWLADWTG2DDE7svbB5RNZMPBETU0CZMpdwjnRk cHhuCTwAjwuj5JW668Ylb4zSDeQyhvV6qavV9prGeugTCy3oekzyNdbW/I584eMcAcqz 3INfnz7jrWWKKBafzc+djKDRdNPjY/4BrQ/6yNQcHdfYf+VdHaxaPY/B1Rw8HKWzXhzn oik6vT19Wq7DIt6GpFUpzrsli17ZFl72q1uqxb1D6dhlst7F0xhjsm3bgnqv+Yqs5hoG S51A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc:content-transfer-encoding; bh=5w1OIfygzSAzOtR1gEmt6DQmNATik/MV9LcnsLZ7twE=; b=OOzIKksvTNUFY/NH5XdnUdfEI2gAl35KU+KmQO92Xln5GkEifN1fZobZ4kAlSa+2BA utNG0KzORJ2WxDUIy1jQnYqdtfLWcTsrQ0IRAbsRNe3ONXYSJ4ITJdAj0/64Pml5noL7 gDgYnPiqkRToVf4Cc+QEv5cHZQVQEItoypUabDfATI7jFtZ2lneGP5J0OFOTDWFzDJP1 bJ7rP7BzQpEtu3j7VFUIDULNv7r99S4VruNkY8RcCW/gHskDea63UI+pi0cXbIasPiAW jec1ipa83lE9CR68qsl3+3y1k8/Ph+m87r4+3Hhe3v8N/qjEZZkkDCatMHGuPoD6PbBz Y0uw== X-Gm-Message-State: AOAM533uaU8O1jMDI/fQmY3UXvS0i5ALI27ptOoYn8PyLgd+2aXzMglq BlkmouQ7vufG32l8kStuBdn1sKvqZZ0= X-Google-Smtp-Source: ABdhPJzKcl/TP6kH+FmylpiM0aHD/7GierDsHJdkwsZVoIQCtyZIj202X1NnTxJc8Yav7hJXeGgtyQYmv+w= X-Received: from yuzhao.bld.corp.google.com ([2620:15c:183:200:57a6:54a6:aad1:c0a8]) (user=yuzhao job=sendgmr) by 2002:a25:b9ca:0:b0:619:649f:1bf6 with SMTP id y10-20020a25b9ca000000b00619649f1bf6mr14098274ybj.196.1646783322500; Tue, 08 Mar 2022 15:48:42 -0800 (PST) Date: Tue, 8 Mar 2022 16:47:23 -0700 In-Reply-To: <20220308234723.3834941-1-yuzhao@google.com> Message-Id: <20220308234723.3834941-14-yuzhao@google.com> Mime-Version: 1.0 References: <20220308234723.3834941-1-yuzhao@google.com> X-Mailer: git-send-email 2.35.1.616.g0bdcbb4464-goog Subject: [PATCH v8 13/14] mm: multi-gen LRU: admin guide From: Yu Zhao To: Andrew Morton Cc: Andi Kleen , Aneesh Kumar , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Linus Torvalds , Matthew Wilcox , Mel Gorman , Michael Larabel , Michal Hocko , Mike Rapoport , Rik van Riel , Vlastimil Babka , Will Deacon , Ying Huang , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, page-reclaim@google.com, x86@kernel.org, Yu Zhao , Brian Geffon , Jan Alexander Steffens , Oleksandr Natalenko , Steven Barrett , Suleiman Souhlal , Daniel Byrne , Donald Carr , " =?utf-8?q?Holger_Hoffst=C3=A4tte?= " , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh , Vaibhav Jain X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 43AF6180007 X-Stat-Signature: wu7fmio53t7uyjhph6zkth35jeo9b983 Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=VmtraZ99; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf16.hostedemail.com: domain of 3WusnYgYKCOchdiQJXPXXPUN.LXVURWdg-VVTeJLT.XaP@flex--yuzhao.bounces.google.com designates 209.85.128.201 as permitted sender) smtp.mailfrom=3WusnYgYKCOchdiQJXPXXPUN.LXVURWdg-VVTeJLT.XaP@flex--yuzhao.bounces.google.com X-HE-Tag: 1646783323-349558 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Add an admin guide. Signed-off-by: Yu Zhao Acked-by: Brian Geffon Acked-by: Jan Alexander Steffens (heftig) Acked-by: Oleksandr Natalenko Acked-by: Steven Barrett Acked-by: Suleiman Souhlal Tested-by: Daniel Byrne Tested-by: Donald Carr Tested-by: Holger Hoffstätte Tested-by: Konstantin Kharlamov Tested-by: Shuang Zhai Tested-by: Sofia Trinh Tested-by: Vaibhav Jain --- Documentation/admin-guide/mm/index.rst | 1 + Documentation/admin-guide/mm/multigen_lru.rst | 146 ++++++++++++++++++ mm/Kconfig | 3 +- 3 files changed, 149 insertions(+), 1 deletion(-) create mode 100644 Documentation/admin-guide/mm/multigen_lru.rst diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst index c21b5823f126..2cf5bae62036 100644 --- a/Documentation/admin-guide/mm/index.rst +++ b/Documentation/admin-guide/mm/index.rst @@ -32,6 +32,7 @@ the Linux memory management. idle_page_tracking ksm memory-hotplug + multigen_lru nommu-mmap numa_memory_policy numaperf diff --git a/Documentation/admin-guide/mm/multigen_lru.rst b/Documentation/admin-guide/mm/multigen_lru.rst new file mode 100644 index 000000000000..c60dcae5a1a9 --- /dev/null +++ b/Documentation/admin-guide/mm/multigen_lru.rst @@ -0,0 +1,146 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============= +Multi-Gen LRU +============= +Quick start +=========== +Build the kernel with the following configurations. + +* ``CONFIG_LRU_GEN=y`` +* ``CONFIG_LRU_GEN_ENABLED=y`` + +All set! + +Runtime options +=============== +``/sys/kernel/mm/lru_gen/`` contains stable ABIs described in the +following subsections. + +Kill switch +----------- +``enable`` accepts different values to enable or disabled the +following components. The default value of this file depends on +``CONFIG_LRU_GEN_ENABLED``. All the components should be enabled +unless some of them have unforeseen side effects. Writing to +``enable`` has no effect when a component is not supported by the +hardware, and valid values will be accepted even when the main switch +is off. + +====== =============================================================== +Values Components +====== =============================================================== +0x0001 The main switch for the multi-gen LRU. +0x0002 Clearing the accessed bit in leaf page table entries in large + batches, when MMU sets it (e.g., on x86). This behavior can + theoretically worsen lock contention (mmap_lock). If it is + disabled, the multi-gen LRU will suffer a minor performance + degradation. +0x0004 Clearing the accessed bit in non-leaf page table entries as + well, when MMU sets it (e.g., on x86). This behavior was not + verified on x86 varieties other than Intel and AMD. If it is + disabled, the multi-gen LRU will suffer a negligible + performance degradation. +[yYnN] Apply to all the components above. +====== =============================================================== + +E.g., +:: + + echo y >/sys/kernel/mm/lru_gen/enabled + cat /sys/kernel/mm/lru_gen/enabled + 0x0007 + echo 5 >/sys/kernel/mm/lru_gen/enabled + cat /sys/kernel/mm/lru_gen/enabled + 0x0005 + +Thrashing prevention +-------------------- +Personal computers are more sensitive to thrashing because it can +cause janks (lags when rendering UI) and negatively impact user +experience. The multi-gen LRU offers thrashing prevention to the +majority of laptop and desktop users who do not have ``oomd``. + +Users can write ``N`` to ``min_ttl_ms`` to prevent the working set of +``N`` milliseconds from getting evicted. The OOM killer is triggered +if this working set cannot be kept in memory. In other words, this +option works as an adjustable pressure relief valve, and when open, it +terminates applications that are hopefully not being used. + +Based on the average human detectable lag (~100ms), ``N=1000`` usually +eliminates intolerable janks due to thrashing. Larger values like +``N=3000`` make janks less noticeable at the risk of premature OOM +kills. + +Experimental features +===================== +``/sys/kernel/debug/lru_gen`` accepts commands described in the +following subsections. Multiple command lines are supported, so does +concatenation with delimiters ``,`` and ``;``. + +``/sys/kernel/debug/lru_gen_full`` provides additional stats for +debugging. ``CONFIG_LRU_GEN_STATS=y`` keeps historical stats from +evicted generations in this file. + +Working set estimation +---------------------- +Working set estimation measures how much memory an application +requires in a given time interval, and it is usually done with little +impact on the performance of the application. E.g., data centers want +to optimize job scheduling (bin packing) to improve memory +utilizations. When a new job comes in, the job scheduler needs to find +out whether each server it manages can allocate a certain amount of +memory for this new job before it can pick a candidate. To do so, this +job scheduler needs to estimate the working sets of the existing jobs. + +When it is read, ``lru_gen`` returns a histogram of numbers of pages +accessed over different time intervals for each memcg and node. +``CONFIG_NR_LRU_GENS`` decides the number of bins for each histogram. +:: + + memcg memcg_id memcg_path + node node_id + min_gen_nr age_in_ms nr_anon_pages nr_file_pages + ... + max_gen_nr age_in_ms nr_anon_pages nr_file_pages + +Each generation contains an estimated number of pages that have been +accessed within ``age_in_ms`` non-cumulatively. E.g., ``min_gen_nr`` +contains the coldest pages and ``max_gen_nr`` contains the hottest +pages, since ``age_in_ms`` of the former is the largest and that of +the latter is the smallest. + +Users can write ``+ memcg_id node_id max_gen_nr +[can_swap[full_scan]]`` to ``lru_gen`` to create a new generation +``max_gen_nr+1``. ``can_swap`` defaults to the swap setting and, if it +is set to ``1``, it forces the scan of anon pages when swap is off. +``full_scan`` defaults to ``1`` and, if it is set to ``0``, it reduces +the overhead as well as the coverage when scanning page tables. + +A typical use case is that a job scheduler writes to ``lru_gen`` at a +certain time interval to create new generations, and it ranks the +servers it manages based on the sizes of their cold memory defined by +this time interval. + +Proactive reclaim +----------------- +Proactive reclaim induces memory reclaim when there is no memory +pressure and usually targets cold memory only. E.g., when a new job +comes in, the job scheduler wants to proactively reclaim memory on the +server it has selected to improve the chance of successfully landing +this new job. + +Users can write ``- memcg_id node_id min_gen_nr [swappiness +[nr_to_reclaim]]`` to ``lru_gen`` to evict generations less than or +equal to ``min_gen_nr``. Note that ``min_gen_nr`` should be less than +``max_gen_nr-1`` as ``max_gen_nr`` and ``max_gen_nr-1`` are not fully +aged and therefore cannot be evicted. ``swappiness`` overrides the +default value in ``/proc/sys/vm/swappiness``. ``nr_to_reclaim`` limits +the number of pages to evict. + +A typical use case is that a job scheduler writes to ``lru_gen`` +before it tries to land a new job on a server, and if it fails to +materialize the cold memory without impacting the existing jobs on +this server, it retries on the next server according to the ranking +result obtained from the working set estimation step described +earlier. diff --git a/mm/Kconfig b/mm/Kconfig index e9d5f1d09ac4..414eee6390a6 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -899,7 +899,8 @@ config LRU_GEN # the following options can use up the spare bits in page flags depends on !MAXSMP && (64BIT || !SPARSEMEM || SPARSEMEM_VMEMMAP) help - A high performance LRU implementation for memory overcommit. + A high performance LRU implementation for memory overcommit. See + Documentation/admin-guide/mm/multigen_lru.rst for details. config LRU_GEN_ENABLED bool "Enable by default"