From patchwork Tue Sep 12 17:52:24 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Roesch X-Patchwork-Id: 13381987 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 D5CB5EE3F00 for ; Tue, 12 Sep 2023 17:52:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2C4486B011C; Tue, 12 Sep 2023 13:52:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 274EC6B0132; Tue, 12 Sep 2023 13:52:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 163AB6B0133; Tue, 12 Sep 2023 13:52:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 00DB06B011C for ; Tue, 12 Sep 2023 13:52:53 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id C934FC0310 for ; Tue, 12 Sep 2023 17:52:53 +0000 (UTC) X-FDA: 81228691026.11.B930083 Received: from 66-220-144-178.mail-mxout.facebook.com (66-220-144-178.mail-mxout.facebook.com [66.220.144.178]) by imf30.hostedemail.com (Postfix) with ESMTP id 3BC7D80005 for ; Tue, 12 Sep 2023 17:52:52 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=none; dmarc=none; spf=neutral (imf30.hostedemail.com: 66.220.144.178 is neither permitted nor denied by domain of shr@devkernel.io) smtp.mailfrom=shr@devkernel.io ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1694541172; 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=l+n9FJ6lOfF30jIQ75PT+DFsBoxSFVNR8rLKeRoXW5k=; b=igjvM7iinjRuuAV0mhFaR/6dzpTZcMUIOMcwqB/ANqRd0nhDDLbka7X4T0+zDS2/Vd9ldH BGpJp1XuBpFjTZVlZEmHrJ41VmcGA8BAin69yOhWWGKLzOBd4o2a5RGptMoLo2vcVoDhJq iAh/2SWaB8l3cstAewjjR85xEv0m1f4= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=none; dmarc=none; spf=neutral (imf30.hostedemail.com: 66.220.144.178 is neither permitted nor denied by domain of shr@devkernel.io) smtp.mailfrom=shr@devkernel.io ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1694541172; a=rsa-sha256; cv=none; b=8LnTcsbgPQL5y07LJDIkEcLxlhaLEl+raRELDLhoJI9BiQoW08iU2rMOO91zpUcagc6XAl ske/8B3g3RG58juV9Jqbk8xm0Ke3tEXxQen6g8fkkP5mywjxZNShzXJARUMIgoNcbzxWvt E/CUBD/duqBv/hqXfBEIVXcMOqOdf9U= Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id D9E9DBCD1627; Tue, 12 Sep 2023 10:52:38 -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 0/4] Smart scanning mode for KSM Date: Tue, 12 Sep 2023 10:52:24 -0700 Message-Id: <20230912175228.952039-1-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3BC7D80005 X-Stat-Signature: 55x7r7iaex396robixbfzpii5eacxi6z X-HE-Tag: 1694541172-670143 X-HE-Meta: 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 YsC2WxFH 9PGGMHv8pWWYApfnLyYYeGDQ4Sw== 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: This patch series adds "smart scanning" for KSM. What is smart scanning? ======================= KSM evaluates all the candidate pages for each scan. It does not use historic information from previous scans. This has the effect that candidate pages that couldn't be used for KSM de-duplication continue to be evaluated for each scan. The idea of "smart scanning" is to keep historic information. With the historic information we can temporarily skip the candidate page for one or several scans. Details: ======== "Smart scanning" is to keep two small counters to store if the page has been used for KSM. One counter stores how often we already tried to use the page for KSM and the other counter stores when a page will be used as a candidate page again. How often we skip the candidate page depends how often a page failed KSM de-duplication. The code skips a maximum of 8 times. During testing this has shown to be a good compromise for different workloads. New sysfs knob: =============== Smart scanning is not enabled by default. With /sys/kernel/mm/ksm/smart_scan smart scanning can be enabled. Monitoring: =========== To monitor how effective smart scanning is a new sysfs knob has been introduced. /sys/kernel/mm/pages_skipped report how many pages have been skipped by smart scanning. Results: ======== - Various workloads have shown a 20% - 25% reduction in page scans For the instagram workload for instance, the number of pages scanned has been reduced from over 20M pages per scan to less than 15M pages. - Less pages scans also resulted in an overall higher de-duplication rate as some shorter lived pages could be de-duplicated additionally - Less pages scanned allows to reduce the pages_to_scan parameter and this resulted in a 25% reduction in terms of CPU. - The improvements have been observed for workloads that enable KSM with madvise as well as prctl Stefan Roesch (4): mm/ksm: add "smart" page scanning mode mm/ksm: add pages_skipped metric mm/ksm: document smart scan mode mm/ksm: document pages_skipped sysfs knob Documentation/admin-guide/mm/ksm.rst | 11 ++++ mm/ksm.c | 87 ++++++++++++++++++++++++++++ 2 files changed, 98 insertions(+) base-commit: 15bcc9730fcd7526a3b92eff105d6701767a53bb