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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7AF31C4167B for ; Mon, 4 Dec 2023 23:49:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D16D16B0087; Mon, 4 Dec 2023 18:49:25 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C2D116B0088; Mon, 4 Dec 2023 18:49:25 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AD1C06B008A; Mon, 4 Dec 2023 18:49:25 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 7D20F6B0087 for ; Mon, 4 Dec 2023 18:49:25 -0500 (EST) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 617D980463 for ; Mon, 4 Dec 2023 23:49:25 +0000 (UTC) X-FDA: 81530779890.27.523382E Received: from 66-220-144-178.mail-mxout.facebook.com (66-220-144-178.mail-mxout.facebook.com [66.220.144.178]) by imf06.hostedemail.com (Postfix) with ESMTP id DB32E18001A for ; Mon, 4 Dec 2023 23:49:23 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=none; spf=neutral (imf06.hostedemail.com: 66.220.144.178 is neither permitted nor denied by domain of shr@devkernel.io) smtp.mailfrom=shr@devkernel.io; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1701733764; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references; bh=XItU20KLGq4RN1gSTNWxwfgJDsbPtt7feCDDDhQzEds=; b=pqi312f2L513zWlNKCZ0G1WQAb//NTKeXMWncTZ8xtwSJU/z6xM9iUoRkEp88nzshA5ziD jjvmBoK6gvxSsvSvpM7nhHznv3wGloPvOwtgIdnxzZLtnE+TO6k6UHJ4XHH/eIF6oUa1vD uoAX2MUk/rfA+LkOygA4r2rrbwt15uw= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1701733764; a=rsa-sha256; cv=none; b=7vVUWeQeO5kJxfuQY5uVVXdOHTQRklsFR72sUAUkc1d8oIa6fqVzGDoN5QwtjlamdfV8QB 0wIsIt1lJDT28VwVJ8rDtAFjvJqkt209B3et4S4WigPsnviMJJ/7GJbDjKXU2CgYAkJ8Lh vSkVLPpj1b4ZpZBi/Fp2YKV+E0CRlxw= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=none; spf=neutral (imf06.hostedemail.com: 66.220.144.178 is neither permitted nor denied by domain of shr@devkernel.io) smtp.mailfrom=shr@devkernel.io; dmarc=none Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id 814FC105D3A79; Mon, 4 Dec 2023 15:49:07 -0800 (PST) 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 v3 0/4] mm/ksm: Add ksm advisor Date: Mon, 4 Dec 2023 15:49:02 -0800 Message-Id: <20231204234906.1237478-1-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: oadyq3cydtwqgnmzm9n736y1j655druf X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: DB32E18001A X-Rspam-User: X-HE-Tag: 1701733763-957070 X-HE-Meta: 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 DY+SQARp xcNSRUdLTswyKBXkkEmv0DzAbpmJG0aWVXAoYFT08BRhqQCKcxc+QaUXD3B+G0kzXY1Y4QGNmY9TItYoyxW5iU7eu+G2rksvTOOGe/gBsDanPV5EA7jgX/HTUBQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: What is the KSM advisor? =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 The ksm advisor automatically manages the pages_to_scan setting to achieve a target scan time. The target scan time defines how many seconds it should take to scan all the candidate KSM pages. In other words the pages_to_scan rate is changed by the advisor to achieve the target scan time. Why do we need a KSM advisor? =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 The number of candidate pages for KSM is dynamic. It can often be observe= d 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. With the scan time advisor the pages_to_scan parameter based can be changed based on demand. Algorithm =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D The algorithm calculates the change value based on the target scan time and the previous scan time. To avoid pertubations an exponentially weighted moving average is applied. The algorithm has a max and min value to: - guarantee responsiveness to changes - to limit CPU resource consumption Parameters to influence the KSM scan advisor =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 The respective parameters are: - ksm_advisor_mode 0: None (default), 1: scan time advisor - ksm_advisor_target_scan_time how many seconds a scan should of all candidate pages take - ksm_advisor_max_cpu upper limit for the cpu usage in percent of the ksmd background thread The initial value and the max value for the pages_to_scan parameter can be limited with: - ksm_advisor_min_pages minimum value for pages_to_scan per batch - ksm_advisor_max_pages maximum value for pages_to_scan per batch The default settings for the above two parameters should be suitable for most workloads. The parameters are exposed as knobs in /sys/kernel/mm/ksm. By default the scan time advisor is disabled. Currently there are two advisors: - none and - scan-time. Resource savings =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Tests with various workloads have shown considerable CPU savings. Most of the workloads I have investigated have more candidate pages during startup. Once the workload is stable in terms of memory, the number of candidate pages is reduced. Without the advisor, the pages_to_scan needs to be sized for the maximum number of candidate pages. So having this advisor definitely helps in reducing CPU consumption. For the instagram workload, the advisor achieves a 25% CPU reduction. Once the memory is stable, the pages_to_scan parameter gets reduced to about 40% of its max value. The new advisor works especially well if the smart scan feature is also enabled. How is defining a target scan time better? =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 For an administrator it is more logical to set a target scan time.. The administrator can determine how many pages are scanned on each scan. Therefore setting a target scan time makes more sense. In addition the administrator might have a good idea about the memory sizing of its respective workloads. Setting cpu limits is easier than setting The pages_to_scan parameter. Th= e pages_to_scan parameter is per batch. For the administrator it is difficu= lt to set the pages_to_scan parameter. Tracing =3D=3D=3D=3D=3D=3D=3D A new tracing event has been added for the scan time advisor. The new trace event is called ksm_advisor. It reports the scan time, the new pages_to_scan setting and the cpu usage of the ksmd background thread. Other approaches =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Approach 1: Adapt pages_to_scan after processing each batch. If KSM merges pages, increase the scan rate, if less KSM pages, reduce the the pages_to_scan rate. This doesn't work too well. While it increases the pages_to_scan for a short period, but generally it ends up with a too low pages_to_scan rate. Approach 2: Adapt pages_to_scan after each scan. The problem with that approach is that the calculated scan rate tends to be high. The more aggressive KSM scans, the more pages it can de-duplicate. There have been earlier attempts at an advisor: propose auto-run mode of ksm and its tests (https://marc.info/?l=3Dlinux-mm&m=3D166029880214485&w=3D2) Changes: =3D=3D=3D=3D=3D=3D=3D=3D V3: - Use string parameters for advisor mode - Removed min cpu load sysfs knob - dropped unused enums in ksm_advisor_type - renamed KSM_ADVISOR_LAST to KSM_ADVISOR_COUNT - init_advisor() is needed but changed how it is initialized - don't allow to change pages_to_scan parameter when scan-time advisor is enabled - add ksm_advisor_start_scan() and ksm_advisor_stop_scan() functions to calculate scan time - removed scan time parameter to scan_time_advisor() function V2: - Use functions for long long calculations to support 32 bit platforms - Use cpu min and cpu max settings for the advisor instead of the pages min and max parameters. - pages min and max values are now used for the initial and max values. Generally they are not required to be changed. - Add cpu percent usage value to tracepoint definition - Update documentation for cpu min and cpu max values=20 - Update commit messages for the above changes *** BLURB HERE *** Stefan Roesch (4): mm/ksm: add ksm advisor mm/ksm: add sysfs knobs for advisor mm/ksm: add tracepoint for ksm advisor mm/ksm: document ksm advisor and its sysfs knobs Documentation/admin-guide/mm/ksm.rst | 54 +++++ include/trace/events/ksm.h | 33 +++ mm/ksm.c | 303 ++++++++++++++++++++++++++- 3 files changed, 389 insertions(+), 1 deletion(-) base-commit: 12d04a7bf0da67321229d2bc8b1a7074d65415a9 --=20 2.39.3