From nobody Sat Jan 3 06:37:40 2026 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 B1F1EE7C4E9 for ; Wed, 4 Oct 2023 19:07:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245486AbjJDTH4 (ORCPT ); Wed, 4 Oct 2023 15:07:56 -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 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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-gui= de/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. =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 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/k= sm/``: =20 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 pag= e. =20 +Advisor +=3D=3D=3D=3D=3D=3D=3D + +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`` paramet= er 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 configurati= on of +the scan time advisor. + +The ``pages_to_scan`` parameter is re-calculated after a scan has been com= pleted. + + -- Izik Eidus, Hugh Dickins, 17 Nov 2009 --=20 2.39.3