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 X-Spam-Level: X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 66355C47087 for ; Fri, 28 May 2021 11:59:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A6FB6127A for ; Fri, 28 May 2021 11:59:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236137AbhE1MBO (ORCPT ); Fri, 28 May 2021 08:01:14 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:41180 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233262AbhE1MBN (ORCPT ); Fri, 28 May 2021 08:01:13 -0400 Received: from imap.suse.de (imap-alt.suse-dmz.suse.de [192.168.254.47]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id B95181FD2E; Fri, 28 May 2021 11:59:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1622203177; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Tyj9l9ik9fiIzg7ahnLVcj3TFNtj4jX5IrQ8z2cWPgA=; b=sdVeV8ySnJTQu+Ca7f81XuRHK4s3f4zOZkd7iI2juhIk9CE0wSMoVODxn2zP5huAUkhyDs lWghtWP1rCAZ2VLjJNPEum/30qcBNpgGe3Or9Lj0Y+YNRxd43BbljEREkEdN3mK8ce9uNI ppVP+Q7TTCc+55a/Czu3plq3vwkrNfM= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1622203177; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Tyj9l9ik9fiIzg7ahnLVcj3TFNtj4jX5IrQ8z2cWPgA=; b=6xtxs6wu8gQnc+RhFPNUB1RttB7BEmlJBYfrKl9wxIEnVMnLk5lKDRaXX8KQAd1oWknvVq ImgSg2IQ6sEZm/Cw== Received: from imap3-int (imap-alt.suse-dmz.suse.de [192.168.254.47]) by imap.suse.de (Postfix) with ESMTP id A0CEE11A98; Fri, 28 May 2021 11:59:37 +0000 (UTC) Received: from director2.suse.de ([192.168.254.72]) by imap3-int with ESMTPSA id tAS5JinbsGCJGAAALh3uQQ (envelope-from ); Fri, 28 May 2021 11:59:37 +0000 To: Mel Gorman , Andrew Morton Cc: Hillf Danton , Dave Hansen , Michal Hocko , LKML , Linux-MM References: <20210525080119.5455-1-mgorman@techsingularity.net> <20210525080119.5455-7-mgorman@techsingularity.net> From: Vlastimil Babka Subject: Re: [PATCH 6/6] mm/page_alloc: Introduce vm.percpu_pagelist_high_fraction Message-ID: <018c4b99-81a5-bc12-03cd-662a938ef05a@suse.cz> Date: Fri, 28 May 2021 13:59:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 MIME-Version: 1.0 In-Reply-To: <20210525080119.5455-7-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/25/21 10:01 AM, Mel Gorman wrote: > This introduces a new sysctl vm.percpu_pagelist_high_fraction. It is > similar to the old vm.percpu_pagelist_fraction. The old sysctl increased > both pcp->batch and pcp->high with the higher pcp->high potentially > reducing zone->lock contention. However, the higher pcp->batch value also > potentially increased allocation latency while the PCP was refilled. > This sysctl only adjusts pcp->high so that zone->lock contention is > potentially reduced but allocation latency during a PCP refill remains > the same. > > # grep -E "high:|batch" /proc/zoneinfo | tail -2 > high: 649 > batch: 63 > > # sysctl vm.percpu_pagelist_high_fraction=8 > # grep -E "high:|batch" /proc/zoneinfo | tail -2 > high: 35071 > batch: 63 > > # sysctl vm.percpu_pagelist_high_fraction=64 > high: 4383 > batch: 63 > > # sysctl vm.percpu_pagelist_high_fraction=0 > high: 649 > batch: 63 > > Signed-off-by: Mel Gorman > Acked-by: Dave Hansen Acked-by: Vlastimil Babka Documentation nit below: > @@ -789,6 +790,25 @@ panic_on_oom=2+kdump gives you very strong tool to investigate > why oom happens. You can get snapshot. > > > +percpu_pagelist_high_fraction > +============================= > + > +This is the fraction of pages in each zone that are allocated for each > +per cpu page list. The min value for this is 8. It means that we do > +not allow more than 1/8th of pages in each zone to be allocated in any > +single per_cpu_pagelist. This, while technically correct (as an upper limit) is somewhat misleading as the limit for a single per_cpu_pagelist also considers the number of local cpus. > This entry only changes the value of hot per > +cpu pagelists. User can specify a number like 100 to allocate 1/100th > +of each zone to each per cpu page list. This is worse. Anyone trying to reproduce this example on a system with multiple cpus per node and checking the result will be puzzled. So I think the part about number of local cpus should be mentioned to avoid confusion. > +The batch value of each per cpu pagelist remains the same regardless of the > +value of the high fraction so allocation latencies are unaffected. > + > +The initial value is zero. Kernel uses this value to set the high pcp->high > +mark based on the low watermark for the zone and the number of local > +online CPUs. If the user writes '0' to this sysctl, it will revert to > +this default behavior. > + > +