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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 C6633C4167B for ; Mon, 7 Dec 2020 12:14:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 962592339F for ; Mon, 7 Dec 2020 12:14:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727347AbgLGMN4 (ORCPT ); Mon, 7 Dec 2020 07:13:56 -0500 Received: from mx2.suse.de ([195.135.220.15]:49440 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727004AbgLGMN4 (ORCPT ); Mon, 7 Dec 2020 07:13:56 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1607343189; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=N5aTOOY1yDto3hlZWd7sMkEsRnR8D/QRsIEYRP0S3jQ=; b=jBO+lhrGUzRYbOAoxA1UXH9qf/XtMGzeReS9iN55wAuBNvNTaz6+xRKs8VHwziT0y73eTI C7aCVZHr9IkrnJhXTGqpPMuyRlCuun0XMA8Gl4MxeXRj5N5uRLg9KPyyPtsv8O0fRya1uS kkffOn+VWKJgCazdeXzSJNcwruVo5yo= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 80B41AC90; Mon, 7 Dec 2020 12:13:09 +0000 (UTC) Date: Mon, 7 Dec 2020 13:13:07 +0100 From: Michal Hocko To: Joonsoo Kim Cc: Pavel Tatashin , Jason Gunthorpe , LKML , linux-mm , Andrew Morton , Vlastimil Babka , David Hildenbrand , Oscar Salvador , Dan Williams , Sasha Levin , Tyler Hicks , mike.kravetz@oracle.com, Steven Rostedt , Ingo Molnar , Peter Zijlstra , Mel Gorman , Matthew Wilcox , David Rientjes , John Hubbard Subject: Re: [PATCH 0/6] prohibit pinning pages in ZONE_MOVABLE Message-ID: <20201207121307.GG25569@dhcp22.suse.cz> References: <20201202052330.474592-1-pasha.tatashin@soleen.com> <20201204035953.GA17056@js1304-desktop> <20201204161005.GD5487@ziepe.ca> <20201207071238.GA10731@js1304-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201207071238.GA10731@js1304-desktop> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 07-12-20 16:12:50, Joonsoo Kim wrote: > On Fri, Dec 04, 2020 at 12:50:56PM -0500, Pavel Tatashin wrote: > > > > Yes, this indeed could be a problem for some configurations. I will > > > > add your comment to the commit log of one of the patches. > > > > > > It sounds like there is some inherent tension here, breaking THP's > > > when doing pin_user_pages() is a really nasty thing to do. DMA > > > benefits greatly from THP. > > > > > > I know nothing about ZONE_MOVABLE, is this auto-setup or an admin > > > option? If the result of this patch is standard systems can no longer > > > pin > 80% of their memory I have some regression concerns.. > > > > ZONE_MOVABLE can be configured via kernel parameter, or when memory > > nodes are onlined after hot-add; so this is something that admins > > configure. ZONE_MOVABLE is designed to gurantee memory hot-plug > > Just note, the origin of ZONE_MOVABLE is to provide availability of > huge page, especially, hugetlb page. AFAIK, not guarantee memory > hot-plug. See following commit that introduces the ZONE_MOVABLE. > > 2a1e274 Create the ZONE_MOVABLE zone > > > functionality, and not availability of THP, however, I did not know > > about the use case where some admins might configure ZONE_MOVABLE to > > The usecase is lightly mentioned in previous discussion. > > http://lkml.kernel.org/r/alpine.DEB.2.23.453.2011221300100.2830030@chino.kir.corp.google.com > > Anyway, I agree with your other arguments and this patchset. Yes, historically the original motivation for the movable zone was to help creating large pages via compaction. I also do remember Mel not being particularly happy about that. The thing is that the movability constrain is just too strict for this usecases because the movable zone, especially a lot of it, might be causing similar to lowmem/highmem problems very well known from 32b world. So an admin had to be always very careful when configuring to not cause zone pressure problems. Later on, with a higher demand on the memory hotplug - especially the hotremove usecases - it has become clear that the only reliable way for the memory offlining is to rule out any unmovable memory out of the way and that is why a rather strong properly of movable zone was relied on. In the end we are in two rather different requirements here. One for optimization and one for correctness. In this case I would much rather focus on the correctness aspect. -- Michal Hocko SUSE Labs