Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751267AbdFBUzw (ORCPT ); Fri, 2 Jun 2017 16:55:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:49405 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750971AbdFBUzv (ORCPT ); Fri, 2 Jun 2017 16:55:51 -0400 Subject: Re: [PATCH] mm: make PR_SET_THP_DISABLE immediately active To: Andrew Morton References: <1496415802-30944-1-git-send-email-rppt@linux.vnet.ibm.com> <20170602125059.66209870607085b84c257593@linux-foundation.org> <8a810c81-6a72-2af0-a450-6f03c71d8cca@suse.cz> <20170602134038.13728cb77678ae1a7d7128a4@linux-foundation.org> Cc: Mike Rapoport , Linux API , Michal Hocko , Andrea Arcangeli , Arnd Bergmann , "Kirill A. Shutemov" , Pavel Emelyanov , linux-mm , lkml , Michal Hocko From: Vlastimil Babka Message-ID: Date: Fri, 2 Jun 2017 22:55:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170602134038.13728cb77678ae1a7d7128a4@linux-foundation.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1360 Lines: 38 On 06/02/2017 10:40 PM, Andrew Morton wrote: > On Fri, 2 Jun 2017 22:31:47 +0200 Vlastimil Babka wrote: >>> Perhaps we should be adding new prctl modes to select this new >>> behaviour and leave the existing PR_SET_THP_DISABLE behaviour as-is? >> >> I think we can reasonably assume that most users of the prctl do just >> the fork() & exec() thing, so they will be unaffected. > > That sounds optimistic. Perhaps people are using the current behaviour > to set on particular mapping to MMF_DISABLE_THP, with > > prctl(PR_SET_THP_DISABLE) > mmap() > prctl(PR_CLR_THP_DISABLE) > > ? > > Seems a reasonable thing to do. Using madvise(MADV_NOHUGEPAGE) seems reasonabler to me, with the same effect. And it's older (2.6.38). > But who knows - people do all sorts of > inventive things. Yeah :( but we can hope they don't even know that the prctl currently behaves they way it does - man page doesn't suggest it would, and most of us in this thread found it surprising. >> And as usual, if >> somebody does complain in the end, we revert and try the other way? > > But by then it's too late - the new behaviour will be out in the field. Revert in stable then? But I don't think this patch should go to stable. I understand right that CRIU will switch to the UFFDIO_COPY approach and doesn't need the prctl change/new madvise anymore?