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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8C438C433EF for ; Wed, 18 May 2022 01:48:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233976AbiERBsN (ORCPT ); Tue, 17 May 2022 21:48:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57982 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233886AbiERBrV (ORCPT ); Tue, 17 May 2022 21:47:21 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 72C40546BC for ; Tue, 17 May 2022 18:47:13 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-2f4dfd09d7fso8829047b3.0 for ; Tue, 17 May 2022 18:47:13 -0700 (PDT) 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=pC2YGHfY+9xAk1NrS3hVRRGbc59d6jA/kKpqRhmXjZU=; b=d4/5u6MDRmW4dQggwuo45gVHOGcNR7n57VvoOlxwEtWbUwad4GE8aoDysmKFGLTaVE q+zAo3ySyTwPb9hp05gRFncfuWt2nDjGuN6VfZpZuMbuyUxFM11g/agQlrVYIWn1IUxs XkipmOMieNU1uw2D5zUVznCFAV+YUSCTxsr5zTWuavGi78sw6myMYTLZC8XhvytNpf3w IdBNhbj1+CBfR+UZPTYwWusujy0kZWjqR/t/5FIxrla+ArWZXJekE7zvVGx0uTRTrMsM zI9Ssfi5ZbP1ZDD5VM0Y1nW3UsmRKOCaVKiAoWD7WX2rZnxkta80sIocB8kK4eb0Qz/t MIog== 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=pC2YGHfY+9xAk1NrS3hVRRGbc59d6jA/kKpqRhmXjZU=; b=ZRnXWUcOO4QqiAAQRhk4VLyxUO74vwpOOgDq2hupHi5ETB4aTEpFIFBs191iM/NpFR +0ftTwuWl6ymxypki1wnVNs+klw1JCh5ML0B8X2hgQSxVFBrCHsOKOeqTBeNLdpBCCx4 o8T7S9L/0EzetbSVulw96kvmNyKSvUusUUT7Vy3ec/ZIqhhua4x6Ph0QzdypMUWXCZ6x 3nh04+xGT9SY/NU8BVZKNpdQLC/6OBUMm5KODLD92p0OqoWmYIoGDibSIa27OB8/UyM+ SC9hkP6q634vk+FZB9TxT16YKFoaLTx2Egn6Tv4/xcNyvypxFtJchmqH8pjaDJXDzzFw zDfQ== X-Gm-Message-State: AOAM532zVvVqVFSfzfGVQco8L4lIcpbTEahQ7y2MPBM0xKMccKY64jJh nP8CCJKcDZTFCrrFb2vmkXwUCQhm9Vw= X-Google-Smtp-Source: ABdhPJyp1Ue7r2nSH4HDYmkzwihmYW9ugw8ScU0gZU8yTvmMpO6V3hTtIt1pn8lV2v+Jf8Sc9X480fPnoAo= X-Received: from yuzhao.bld.corp.google.com ([2620:15c:183:200:f7bc:90c9:d86e:4ea8]) (user=yuzhao job=sendgmr) by 2002:a0d:ccc3:0:b0:2ff:4e0:2be5 with SMTP id o186-20020a0dccc3000000b002ff04e02be5mr12603557ywd.225.1652838432493; Tue, 17 May 2022 18:47:12 -0700 (PDT) Date: Tue, 17 May 2022 19:46:32 -0600 In-Reply-To: <20220518014632.922072-1-yuzhao@google.com> Message-Id: <20220518014632.922072-14-yuzhao@google.com> Mime-Version: 1.0 References: <20220518014632.922072-1-yuzhao@google.com> X-Mailer: git-send-email 2.36.0.550.gb090851708-goog Subject: [PATCH v11 13/14] mm: multi-gen LRU: admin guide From: Yu Zhao To: Andrew Morton , linux-mm@kvack.org Cc: Andi Kleen , Aneesh Kumar , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Johannes Weiner , Jonathan Corbet , Linus Torvalds , Matthew Wilcox , Mel Gorman , Michael Larabel , Michal Hocko , Mike Rapoport , Peter Zijlstra , Tejun Heo , Vlastimil Babka , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, page-reclaim@google.com, Yu Zhao , Brian Geffon , Jan Alexander Steffens , Oleksandr Natalenko , Steven Barrett , Suleiman Souhlal , Daniel Byrne , Donald Carr , "=?UTF-8?q?Holger=20Hoffst=C3=A4tte?=" , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh , Vaibhav Jain Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Hoffst=C3=A4tte 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 | 156 ++++++++++++++++++ mm/Kconfig | 3 +- 3 files changed, 159 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-g= uide/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..6355f2b5019d --- /dev/null +++ b/Documentation/admin-guide/mm/multigen_lru.rst @@ -0,0 +1,156 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Multi-Gen LRU +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +The multi-gen LRU is an alternative LRU implementation that optimizes +page reclaim and improves performance under memory pressure. Page +reclaim decides the kernel's caching policy and ability to overcommit +memory. It directly impacts the kswapd CPU usage and RAM efficiency. + +Quick start +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Build the kernel with the following configurations. + +* ``CONFIG_LRU_GEN=3Dy`` +* ``CONFIG_LRU_GEN_ENABLED=3Dy`` + +All set! + +Runtime options +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +``/sys/kernel/mm/lru_gen/`` contains stable ABIs described in the +following subsections. + +Kill switch +----------- +``enabled`` accepts different values to enable or disable the +following components. Its default value depends on +``CONFIG_LRU_GEN_ENABLED``. All the components should be enabled +unless some of them have unforeseen side effects. Writing to +``enabled`` 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. + +=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Values Components +=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +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 for workloads that contiguously map hot pages, + whose accessed bits can be otherwise cleared by fewer larger + batches. +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. +=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +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=3D1000`` usually +eliminates intolerable janks due to thrashing. Larger values like +``N=3D3000`` make janks less noticeable at the risk of premature OOM +kills. + +The default value ``0`` means disabled. + +Experimental features +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +``/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=3Dy`` keeps historical stats from +evicted generations in this file. + +Working set estimation +---------------------- +Working set estimation measures how much memory an application needs +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, the 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. +``MAX_NR_GENS`` decides the number of bins for each histogram. The +histograms are noncumulative. +:: + + 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 bin contains an estimated number of pages that have been accessed +within ``age_in_ms``. 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 [force_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, +and vice versa. ``force_scan`` defaults to ``1`` and, if it is set to +``0``, it employs heuristics to reduce the overhead, which is likely +to reduce the coverage as well. + +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 pages defined by +this time interval. + +Proactive reclaim +----------------- +Proactive reclaim induces page reclaim when there is no memory +pressure. It usually targets cold pages only. E.g., when a new job +comes in, the job scheduler wants to proactively reclaim cold pages on +the server it 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. If it fails to +materialize enough cold pages because of the overestimation, it +retries on the next server according to the ranking result obtained +from the working set estimation step. This less forceful approach +limits the impacts on the existing jobs. diff --git a/mm/Kconfig b/mm/Kconfig index 426ea5f57d88..05291697055a 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -916,7 +916,8 @@ config LRU_GEN # make sure folio->flags has enough spare bits depends on 64BIT || !SPARSEMEM || SPARSEMEM_VMEMMAP help - A high performance LRU implementation to overcommit memory. + A high performance LRU implementation to overcommit memory. See + Documentation/admin-guide/mm/multigen_lru.rst for details. =20 config LRU_GEN_ENABLED bool "Enable by default" --=20 2.36.0.550.gb090851708-goog