From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH V5 0/7] Allow user to request memory to be locked on page fault Date: Tue, 28 Jul 2015 13:17:25 +0200 Message-ID: <20150728111725.GG24972@dhcp22.suse.cz> 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> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20150727145409.GB21664@akamai.com> Sender: linux-alpha-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Eric B Munson Cc: Vlastimil Babka , 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 [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? 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. Anyway munlock with flags opens new doors of trickiness. -- Michal Hocko SUSE Labs