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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1D156C33CB1 for ; Thu, 16 Jan 2020 10:22:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DBB6420661 for ; Thu, 16 Jan 2020 10:22:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DBB6420661 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 742F08E0062; Thu, 16 Jan 2020 05:22:43 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6F35F8E003F; Thu, 16 Jan 2020 05:22:43 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6092A8E0062; Thu, 16 Jan 2020 05:22:43 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0134.hostedemail.com [216.40.44.134]) by kanga.kvack.org (Postfix) with ESMTP id 486488E003F for ; Thu, 16 Jan 2020 05:22:43 -0500 (EST) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id E76218248068 for ; Thu, 16 Jan 2020 10:22:42 +0000 (UTC) X-FDA: 76383108564.05.sand58_17a5a83dd2043 X-HE-Tag: sand58_17a5a83dd2043 X-Filterd-Recvd-Size: 2905 Received: from Galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by imf16.hostedemail.com (Postfix) with ESMTP for ; Thu, 16 Jan 2020 10:22:42 +0000 (UTC) Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1is2IR-0003rz-Ht; Thu, 16 Jan 2020 11:22:39 +0100 Date: Thu, 16 Jan 2020 11:22:39 +0100 From: Sebastian Andrzej Siewior To: Vlastimil Babka Cc: linux-mm@kvack.org, Thomas Gleixner , Andrew Morton , Luis Chamberlain , Kees Cook , Iurii Zaikin , Mel Gorman , Linux API Subject: Re: [PATCH] mm/compaction: Disable compact_unevictable_allowed on RT Message-ID: <20200116102239.m2trw3cvosn7q5a5@linutronix.de> References: <20200115161035.893221-1-bigeasy@linutronix.de> <4cf4507b-0632-34e6-5985-df933559af9f@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <4cf4507b-0632-34e6-5985-df933559af9f@suse.cz> 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 2020-01-15 23:04:19 [+0100], Vlastimil Babka wrote: > On 1/15/2020 5:10 PM, Sebastian Andrzej Siewior wrote: > > Since commit > > 5bbe3547aa3ba ("mm: allow compaction of unevictable pages") > > > > it is allowed to examine mlocked pages and compact them by default. > > On -RT even minor pagefaults are problematic because it may take a few > > 100us to resolve them and until then the task is blocked. > > Fine, this makes sense on RT I guess. There might be some trade-off for > high-order allocation latencies though. We could perhaps migrate such mlocked > pages to pages allocated without __GFP_MOVABLE during the mlock() to at least > somewhat prevent them being scattered all over the zones. For MCL_FUTURE, > allocate them as unmovable from the beginning. But that can wait until issues > are reported. > I assume you have similar solution for NUMA balancing and whatever else can > cause minor faults? I've found this one while testing. Could you please point to the NUMA balancing that might be an issue? > > Make compact_unevictable_allowed = 0 default and remove it from /proc on > > RT. > > Removing it is maybe going too far in terms of RT kernel differences confusing > users? Change the default sure, perhaps making it read-only, but removing? Okay. I will make it RO then. > > Link: https://lore.kernel.org/linux-mm/20190710144138.qyn4tuttdq6h7kqx@linutronix.de/ > > In any case the sysctl Documentation/ should be updated? And perhaps also the > mlock manpage as you noted in the older thread above? Sure. Let me add the sysctl documentation to this patch and then I will look into the manpage. > Thanks, > Vlastimil Sebastian