From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 9AA626B02B4 for ; Thu, 1 Jun 2017 02:58:51 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id h76so43424814pfh.15 for ; Wed, 31 May 2017 23:58:51 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com. [148.163.156.1]) by mx.google.com with ESMTPS id z184si19560432pgb.151.2017.05.31.23.58.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 May 2017 23:58:50 -0700 (PDT) Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v516t68e012578 for ; Thu, 1 Jun 2017 02:58:50 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0a-001b2d01.pphosted.com with ESMTP id 2at43rfxfx-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 01 Jun 2017 02:58:50 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 1 Jun 2017 07:58:46 +0100 Date: Thu, 1 Jun 2017 09:58:39 +0300 From: Mike Rapoport Subject: Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE References: <20170524142735.GF3063@rapoport-lnx> <20170530074408.GA7969@dhcp22.suse.cz> <20170530101921.GA25738@rapoport-lnx> <20170530103930.GB7969@dhcp22.suse.cz> <20170530140456.GA8412@redhat.com> <20170530143941.GK7969@dhcp22.suse.cz> <20170530154326.GB8412@redhat.com> <20170531120822.GL27783@dhcp22.suse.cz> <8FA5E4C2-D289-4AF5-AA09-6C199E58F9A5@linux.vnet.ibm.com> <20170531141809.GB302@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170531141809.GB302@redhat.com> Message-Id: <20170601065838.GB30495@rapoport-lnx> Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Arcangeli Cc: Michal Hocko , Vlastimil Babka , "Kirill A. Shutemov" , Andrew Morton , Arnd Bergmann , "Kirill A. Shutemov" , Pavel Emelyanov , linux-mm , lkml , Linux API On Wed, May 31, 2017 at 04:18:09PM +0200, Andrea Arcangeli wrote: > On Wed, May 31, 2017 at 03:39:22PM +0300, Mike Rapoport wrote: > > For the CRIU usecase, disabling THP for a while and re-enabling it > > back will do the trick, provided VMAs flags are not affected, like > > in the patch you've sent. Moreover, we may even get away with > > Are you going to check uname -r to know when the kABI changed in your > favor (so CRIU cannot ever work with enterprise backports unless you > expand the uname -r coverage), or how do you know the patch is > applied? CRIU does not rely on uname -r. We have code that checks what kernel features we can actually use. For instance, we use UFFDIO_API to see if we can do post-copy at all. > Optimistically assuming people is going to run new CRIU code only on > new kernels looks very risky, it would leads to silent random memory > corruption, so I doubt you can get away without a uname -r check. > > This is fairly simple change too, its main cons is that it adds a > branch to the page fault fast path, the old behavior of the prctl and > the new madvise were both zero cost. > > Still if the prctl is preferred despite the added branch, to avoid > uname -r clashes, to me it sounds better to add a new prctl ID and > keep the old one too. The old one could be implemented the same way as > the new one if you want to save a few bytes of .text. But the old one > should probably do a printk_once to print a deprecation warning so the > old ID with weaker (zero runtime cost) semantics can be removed later. > -- 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