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[23.128.96.34]) by mx.google.com with ESMTPS id e4-20020a656884000000b005b11e5a69fdsi1703920pgt.508.2023.10.27.17.13.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Oct 2023 17:13:24 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.34 as permitted sender) client-ip=23.128.96.34; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.34 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (depot.vger.email [IPv6:2620:137:e000::3:0]) by howler.vger.email (Postfix) with ESMTP id 286A683F02BC; Fri, 27 Oct 2023 17:13:17 -0700 (PDT) X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.10 at howler.vger.email Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232648AbjJ1ANA (ORCPT + 27 others); Fri, 27 Oct 2023 20:13:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230104AbjJ1AM7 (ORCPT ); Fri, 27 Oct 2023 20:12:59 -0400 Received: from 66-220-144-179.mail-mxout.facebook.com (66-220-144-179.mail-mxout.facebook.com [66.220.144.179]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 29BEE1B6 for ; Fri, 27 Oct 2023 17:12:57 -0700 (PDT) Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id 762FBE5A2603; Fri, 27 Oct 2023 17:10:28 -0700 (PDT) From: Stefan Roesch To: kernel-team@fb.com Cc: shr@devkernel.io, akpm@linux-foundation.org, david@redhat.com, hannes@cmpxchg.org, riel@surriel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 4/4] mm/ksm: document ksm advisor and its sysfs knobs Date: Fri, 27 Oct 2023 17:09:45 -0700 Message-Id: <20231028000945.2428830-5-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20231028000945.2428830-1-shr@devkernel.io> References: <20231028000945.2428830-1-shr@devkernel.io> MIME-Version: 1.0 X-Spam-Status: No, score=-0.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on howler.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (howler.vger.email [0.0.0.0]); Fri, 27 Oct 2023 17:13:17 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1780956009513056762 X-GMAIL-MSGID: 1780956009513056762 This documents the KSM advisor and its new knobs in /sys/fs/kernel/mm. Signed-off-by: Stefan Roesch --- Documentation/admin-guide/mm/ksm.rst | 66 ++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst index e59231ac6bb7..7e956692b656 100644 --- a/Documentation/admin-guide/mm/ksm.rst +++ b/Documentation/admin-guide/mm/ksm.rst @@ -164,6 +164,33 @@ smart_scan optimization is enabled. The ``pages_skipped`` metric shows how effective the setting is. +advisor_mode + The ``advisor_mode`` selects the current advisor. Two modes are + supported: 0 (None) and 1 (Scan time). The default is None. By + setting ``advisor_mode`` to 1, the scan time advisor is enabled. + The section about ``advisor`` explains in detail how the scan time + advisor works. + +advisor_min_cpu + specifies the lower limit of the cpu percent usage of the ksmd + background thread. The default is 15. + +adivsor_max_cpu + specifies the upper limit of the cpu percent usage of the ksmd + background thread. The default is 70. + +advisor_target_scan_time + specifies the target scan time in seconds to scan all the candidate + pages. The default value is 200 seconds. + +advisor_min_pages + specifies the lower limit of the ``pages_to_scan`` parameter of the + scan time advisor. The default is 500. + +adivsor_max_pages + specifies the upper limit of the ``pages_to_scan`` parameter of the + scan time advisor. The default is 30000. + The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``: general_profit @@ -263,6 +290,45 @@ ksm_swpin_copy note that KSM page might be copied when swapping in because do_swap_page() cannot do all the locking needed to reconstitute a cross-anon_vma KSM page. +Advisor +======= + +The number of candidate pages for KSM is dynamic. It can be often observed +that during the startup of an application more candidate pages need to be +processed. Without an advisor the ``pages_to_scan`` parameter needs to be +sized for the maximum number of candidate pages. The scan time advisor can +changes the ``pages_to_scan`` parameter based on demand. + +The advisor can be enabled, so KSM can automatically adapt to changes in the +number of candidate pages to scan. Two advisors are implemented: 0 (None) and +1 (Scan time). With None no advisor is enabled. The default is None. + +The Scan time advisor changes the ``pages_to_scan`` parameter based on the +observed scan times. The possible values for the ``pages_to_scan`` parameter is +limited by the ``advisor_min_pages`` and ``advisor_max_pages`` parameters. In +addition there is also the ``advisor_target_scan_time`` parameter. This +parameter sets the target time to scan all the KSM candidate pages. The +parameter ``advisor_target_scan_time`` decides how aggressive the scan time +advisor scans candidate pages. Lower values make the scan time advisor to scan +more aggresively. This is the most important parameter for the configuration of +the scan time advisor. + +The Scan time advisor changes the ``pages_to_scan`` parameter based on the +observed scan times. The possible values for the ``pages_to_scan`` parameter is +limited by the ``advisor_min_cpu`` and ``advisor_max_cpu`` parameters. In +addition there is also the ``advisor_target_scan_time`` parameter. This +parameter sets the target time to scan all the KSM candidate pages. The +parameter ``advisor_target_scan_time`` decides how aggressive the scan time +advisor scans candidate pages. Lower values make the scan time advisor to scan +more aggresively. This is the most important parameter for the configuration of +the scan time advisor. + +The initial value and the maximum value can be changed with ``advisor_min_pages`` +and ``advisor_max_pages``. The default values are sufficient for most workloads. + +The ``pages_to_scan`` parameter is re-calculated after a scan has been completed. + + -- Izik Eidus, Hugh Dickins, 17 Nov 2009