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[23.128.96.32]) by mx.google.com with ESMTPS id v13-20020a170903238d00b001b3d27ca12fsi4033742plh.207.2023.10.04.12.09.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Oct 2023 12:09:20 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.32 as permitted sender) client-ip=23.128.96.32; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.32 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 agentk.vger.email (Postfix) with ESMTP id 148FD804C224; Wed, 4 Oct 2023 12:08:55 -0700 (PDT) X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.10 at agentk.vger.email Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245483AbjJDTHy (ORCPT + 19 others); Wed, 4 Oct 2023 15:07:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343901AbjJDTHZ (ORCPT ); Wed, 4 Oct 2023 15:07:25 -0400 Received: from 66-220-144-178.mail-mxout.facebook.com (66-220-144-178.mail-mxout.facebook.com [66.220.144.178]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D7DF30F4 for ; Wed, 4 Oct 2023 12:03:19 -0700 (PDT) Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id 0F49CD08C004; Wed, 4 Oct 2023 12:03:03 -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 v1 4/4] mm/ksm: document ksm advisor and its sysfs knobs Date: Wed, 4 Oct 2023 12:02:49 -0700 Message-Id: <20231004190249.829015-5-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20231004190249.829015-1-shr@devkernel.io> References: <20231004190249.829015-1-shr@devkernel.io> MIME-Version: 1.0 X-Spam-Status: No, score=2.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_SBL_CSS,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on agentk.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 (agentk.vger.email [0.0.0.0]); Wed, 04 Oct 2023 12:08:55 -0700 (PDT) X-Spam-Level: ** X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1778853148892726045 X-GMAIL-MSGID: 1778853148892726045 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 | 45 ++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst index e59231ac6bb7..8de93650d3b0 100644 --- a/Documentation/admin-guide/mm/ksm.rst +++ b/Documentation/admin-guide/mm/ksm.rst @@ -164,6 +164,25 @@ 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_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 5000. + +advisor_target_scan_time + specifies the target scan time in seconds to scan all the candidate + pages. The default value is 200 seconds. + The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``: general_profit @@ -263,6 +282,32 @@ 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 ``pages_to_scan`` parameter is re-calculated after a scan has been completed. + + -- Izik Eidus, Hugh Dickins, 17 Nov 2009