Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755701AbbG1LXm (ORCPT ); Tue, 28 Jul 2015 07:23:42 -0400 Received: from mx2.suse.de ([195.135.220.15]:39588 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755290AbbG1LXj (ORCPT ); Tue, 28 Jul 2015 07:23:39 -0400 Subject: Re: [PATCH V5 0/7] Allow user to request memory to be locked on page fault To: Michal Hocko , Eric B Munson References: <1437773325-8623-1-git-send-email-emunson@akamai.com> <55B5F4FF.9070604@suse.cz> <20150727133555.GA17133@akamai.com> <55B63D37.20303@suse.cz> <20150727145409.GB21664@akamai.com> <20150728111725.GG24972@dhcp22.suse.cz> Cc: Andrew Morton , Shuah Khan , Michael Kerrisk , Jonathan Corbet , Ralf Baechle , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org From: Vlastimil Babka Message-ID: <55B76631.6040802@suse.cz> Date: Tue, 28 Jul 2015 13:23:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <20150728111725.GG24972@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2081 Lines: 56 On 07/28/2015 01:17 PM, Michal Hocko wrote: > [I am sorry but I didn't get to this sooner.] > > On Mon 27-07-15 10:54:09, Eric B Munson wrote: >> Now that VM_LOCKONFAULT is a modifier to VM_LOCKED and >> cannot be specified independentally, it might make more sense to mirror >> that relationship to userspace. Which would lead to soemthing like the >> following: > > A modifier makes more sense. > >> To lock and populate a region: >> mlock2(start, len, 0); >> >> To lock on fault a region: >> mlock2(start, len, MLOCK_ONFAULT); >> >> If LOCKONFAULT is seen as a modifier to mlock, then having the flags >> argument as 0 mean do mlock classic makes more sense to me. >> >> To mlock current on fault only: >> mlockall(MCL_CURRENT | MCL_ONFAULT); >> >> To mlock future on fault only: >> mlockall(MCL_FUTURE | MCL_ONFAULT); >> >> To lock everything on fault: >> mlockall(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT); > > Makes sense to me. The only remaining and still tricky part would be > the munlock{all}(flags) behavior. What should munlock(MLOCK_ONFAULT) > do? Keep locked and poppulate the range or simply ignore the flag an > just unlock? munlock(all) already lost both MLOCK_LOCKED and MLOCK_ONFAULT flags in this revision, so I suppose in the next revision it will also not accept MLOCK_ONFAULT, and will just munlock whatever was mlocked in either mode. > I can see some sense to allow munlockall(MCL_FUTURE[|MLOCK_ONFAULT]), > munlockall(MCL_CURRENT) resp. munlockall(MCL_CURRENT|MCL_FUTURE) but > other combinations sound weird to me. The effect of munlockall(MCL_FUTURE|MLOCK_ONFAULT), which you probably intended for converting the onfault to full prepopulation for future mappings, can be achieved by calling mlockall(MCL_FUTURE) (without MLOCK_ONFAULT). > Anyway munlock with flags opens new doors of trickiness. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/