Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751204AbdFCKfH convert rfc822-to-8bit (ORCPT ); Sat, 3 Jun 2017 06:35:07 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:48368 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751173AbdFCKfG (ORCPT ); Sat, 3 Jun 2017 06:35:06 -0400 Date: Sat, 03 Jun 2017 13:34:52 +0300 User-Agent: K-9 Mail for Android In-Reply-To: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Subject: Re: [PATCH] mm: make PR_SET_THP_DISABLE immediately active To: Vlastimil Babka , Andrew Morton CC: Linux API , Michal Hocko , Andrea Arcangeli , Arnd Bergmann , "Kirill A. Shutemov" , Pavel Emelyanov , linux-mm , lkml , Michal Hocko From: Mike Rapoprt X-TM-AS-GCONF: 00 x-cbid: 17060310-0016-0000-0000-000004B3D9B4 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17060310-0017-0000-0000-000027E2405B Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-06-03_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1706030200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1650 Lines: 52 On June 2, 2017 11:55:12 PM GMT+03:00, Vlastimil Babka wrote: >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? Yes, we are going to use UFFDIO_COPY. We still might want to have control over THP in the future without changing per-VMA flags, though. -- Sincerely yours, Mike.