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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 060D2C35242 for ; Wed, 12 Feb 2020 02:25:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 922082082F for ; Wed, 12 Feb 2020 02:25:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 922082082F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id DC27E6B038D; Tue, 11 Feb 2020 21:25:40 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D4DC96B038F; Tue, 11 Feb 2020 21:25:40 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C3AEC6B0390; Tue, 11 Feb 2020 21:25:40 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0081.hostedemail.com [216.40.44.81]) by kanga.kvack.org (Postfix) with ESMTP id A7DA56B038D for ; Tue, 11 Feb 2020 21:25:40 -0500 (EST) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 4C0BB40D9 for ; Wed, 12 Feb 2020 02:25:40 +0000 (UTC) X-FDA: 76479884040.02.bag77_316d4c8238a09 X-HE-Tag: bag77_316d4c8238a09 X-Filterd-Recvd-Size: 3421 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Wed, 12 Feb 2020 02:25:39 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Feb 2020 18:25:38 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,428,1574150400"; d="scan'208";a="222139494" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga007.jf.intel.com with ESMTP; 11 Feb 2020 18:25:36 -0800 Date: Wed, 12 Feb 2020 10:25:55 +0800 From: Wei Yang To: Mel Gorman Cc: Wei Yang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, shakeelb@google.com, yang.shi@linux.alibaba.com Subject: Re: [RFC Patch] mm/vmscan.c: not inherit classzone_idx from previous reclaim Message-ID: <20200212022554.GA7855@richard> Reply-To: Wei Yang References: <20200209074145.31389-1-richardw.yang@linux.intel.com> <20200211104223.GL3466@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200211104223.GL3466@techsingularity.net> User-Agent: Mutt/1.9.4 (2018-02-28) 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: On Tue, Feb 11, 2020 at 10:42:23AM +0000, Mel Gorman wrote: >On Sun, Feb 09, 2020 at 03:41:45PM +0800, Wei Yang wrote: >> Before commit e716f2eb24de ("mm, vmscan: prevent kswapd sleeping >> prematurely due to mismatched classzone_idx"), classzone_idx could have >> two possibilities on a new loop based on whether there is a wakeup >> during reclaiming: >> >> * 0 if no wakeup >> * the classzone_idx request by wakeup >> >> As described in the changelog, this commit is willing to change the >> first case to (MAX_NR_ZONES - 1) to avoid some premature sleep. But it >> does not achieve the goal. >> >> There are two versions of kswapd_classzone_idx() since this change: >> >> * commit e716f2eb24de ("mm, vmscan: prevent kswapd sleeping >> prematurely due to mismatched classzone_idx") >> * commit dffcac2cb88e ("mm/vmscan.c: prevent useless kswapd loops") >> >> Both of them would return the classzone_idx we passed as the 2nd >> parameter when (pgdat->kswapd_classzone_idx == MAX_NR_ZONES). This >> means if there is no wakeup during reclaiming, we would use >> classzone_idx in previous round to sleep. >> > >This is somewhat intended. > >> This patch fixes the logic by using (MAX_NR_ZONES - 1) for the first >> case. >> > >Ok, what is the user-visible impact that is fixed by this patch or is >this based on code review only? Please describe the test case exactly >and the before and after results. I ask because this area is a magnet for >regressions and intuitive ideas often lead to counter-intuitive results. > This is based on code review only. I know your concern. This is an area more like art then engineering :-) Would you mind sharing some idea why we intend to inherit the classzone_idx? And for kswapd_order, we would restart at 0 if no wakeup during reclaim. I am curious about the idea behind this design :-) >-- >Mel Gorman >SUSE Labs -- Wei Yang Help you, Help me