From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id A14BF6B0314 for ; Fri, 2 Jun 2017 16:55:51 -0400 (EDT) Received: by mail-wr0-f197.google.com with SMTP id k57so3294564wrk.6 for ; Fri, 02 Jun 2017 13:55:51 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id s11si23496173edd.47.2017.06.02.13.55.49 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 02 Jun 2017 13:55:50 -0700 (PDT) Subject: Re: [PATCH] mm: make PR_SET_THP_DISABLE immediately active 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> From: Vlastimil Babka Message-ID: Date: Fri, 2 Jun 2017 22:55:12 +0200 MIME-Version: 1.0 In-Reply-To: <20170602134038.13728cb77678ae1a7d7128a4@linux-foundation.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Mike Rapoport , Linux API , Michal Hocko , Andrea Arcangeli , Arnd Bergmann , "Kirill A. Shutemov" , Pavel Emelyanov , linux-mm , lkml , Michal Hocko 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? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org