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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 190B1C43382 for ; Wed, 26 Sep 2018 06:06:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C5A09214AB for ; Wed, 26 Sep 2018 06:06:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C5A09214AB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727054AbeIZMRn (ORCPT ); Wed, 26 Sep 2018 08:17:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:55284 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726355AbeIZMRm (ORCPT ); Wed, 26 Sep 2018 08:17:42 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id DEF98AD05; Wed, 26 Sep 2018 06:06:25 +0000 (UTC) Date: Wed, 26 Sep 2018 08:06:24 +0200 From: Michal Hocko To: Andrew Morton Cc: David Rientjes , Vlastimil Babka , Alexey Dobriyan , "Kirill A. Shutemov" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org Subject: Re: [patch v2] mm, thp: always specify ineligible vmas as nh in smaps Message-ID: <20180926060624.GA18685@dhcp22.suse.cz> References: <20180924195603.GJ18685@dhcp22.suse.cz> <20180924200258.GK18685@dhcp22.suse.cz> <0aa3eb55-82c0-eba3-b12c-2ba22e052a8e@suse.cz> <20180925202959.GY18685@dhcp22.suse.cz> <20180925150406.872aab9f4f945193e5915d69@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180925150406.872aab9f4f945193e5915d69@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 25-09-18 15:04:06, Andrew Morton wrote: > On Tue, 25 Sep 2018 14:45:19 -0700 (PDT) David Rientjes wrote: > > > > > It is also used in > > > > automated testing to ensure that vmas get disabled for thp appropriately > > > > and we used "nh" since that is how PR_SET_THP_DISABLE previously enforced > > > > this, and those tests now break. > > > > > > This sounds like a bit of an abuse to me. It shows how an internal > > > implementation detail leaks out to the userspace which is something we > > > should try to avoid. > > > > > > > Well, it's already how this has worked for years before commit > > 1860033237d4 broke it. Changing the implementation in the kernel is fine > > as long as you don't break userspace who relies on what is exported to it > > and is the only way to determine if MADV_NOHUGEPAGE is preventing it from > > being backed by hugepages. > > 1860033237d4 was over a year ago so perhaps we don't need to be > too worried about restoring the old interface. In which case > we have an opportunity to make improvements such as that suggested > by Michal? Yeah, can we add a way to export PR_SET_THP_DISABLE to userspace somehow? E.g. /proc//status. It is a process wide thing so reporting it per VMA sounds strange at best. This would also keep a sane (and currently documented) semantic for the smaps flag to be really hg - huge page advise flag nh - no-huge page advise flag -- Michal Hocko SUSE Labs