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 89B84C27C48 for ; Sat, 28 Oct 2023 00:13:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346724AbjJ1ANB (ORCPT ); Fri, 27 Oct 2023 20:13:01 -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 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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-g= uide/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. =20 +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 ti= me + 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 candid= ate + 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/``: =20 general_profit @@ -263,6 +290,45 @@ ksm_swpin_copy note that KSM page might be copied when swapping in because do_swap_pag= e() cannot do all the locking needed to reconstitute a cross-anon_vma KSM p= age. =20 +Advisor +=3D=3D=3D=3D=3D=3D=3D + +The number of candidate pages for KSM is dynamic. It can be often observ= ed +that during the startup of an application more candidate pages need to b= e +processed. Without an advisor the ``pages_to_scan`` parameter needs to b= e +sized for the maximum number of candidate pages. The scan time advisor c= an +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 t= he +observed scan times. The possible values for the ``pages_to_scan`` param= eter is +limited by the ``advisor_min_pages`` and ``advisor_max_pages`` parameter= s. 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 t= ime +advisor scans candidate pages. Lower values make the scan time advisor t= o scan +more aggresively. This is the most important parameter for the configura= tion of +the scan time advisor. + +The Scan time advisor changes the ``pages_to_scan`` parameter based on t= he +observed scan times. The possible values for the ``pages_to_scan`` param= eter is +limited by the ``advisor_min_cpu`` and ``advisor_max_cpu`` parameters. I= n +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 t= ime +advisor scans candidate pages. Lower values make the scan time advisor t= o scan +more aggresively. This is the most important parameter for the configura= tion of +the scan time advisor. + +The initial value and the maximum value can be changed with ``advisor_mi= n_pages`` +and ``advisor_max_pages``. The default values are sufficient for most wo= rkloads. + +The ``pages_to_scan`` parameter is re-calculated after a scan has been c= ompleted. + + -- Izik Eidus, Hugh Dickins, 17 Nov 2009 --=20 2.39.3