From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Corbet Subject: Re: [PATCH V3 3/5] mm: mlock: Introduce VM_LOCKONFAULT and add mlock flags to enable it Date: Wed, 8 Jul 2015 15:17:50 -0600 Message-ID: <20150708151750.75e65859@lwn.net> References: <1436288623-13007-1-git-send-email-emunson@akamai.com> <1436288623-13007-4-git-send-email-emunson@akamai.com> <20150708132351.61c13db6@lwn.net> <20150708203456.GC4669@akamai.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <20150708203456.GC4669@akamai.com> Sender: sparclinux-owner@vger.kernel.org To: Eric B Munson Cc: Andrew Morton , Michal Hocko , Vlastimil Babka , 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 List-Id: linux-api@vger.kernel.org On Wed, 8 Jul 2015 16:34:56 -0400 Eric B Munson wrote: > > Quick, possibly dumb question: I've been beating my head against these for > > a little bit, and I can't figure out what's supposed to happen in this > > case: > > > > mlock2(addr, len, MLOCK_ONFAULT); > > munlock2(addr, len, MLOCK_LOCKED); > > > > It looks to me like it will clear VM_LOCKED without actually unlocking any > > pages. Is that the intended result? > > This is not quite right, what happens when you call munlock2(addr, len, > MLOCK_LOCKED); is we call apply_vma_flags(addr, len, VM_LOCKED, false). >>From your explanation, it looks like what I said *was* right...what I was missing was the fact that VM_LOCKED isn't set in the first place. So that call would be a no-op, clearing a flag that's already cleared. One other question...if I call mlock2(MLOCK_ONFAULT) on a range that already has resident pages, I believe that those pages will not be locked until they are reclaimed and faulted back in again, right? I suspect that could be surprising to users. Thanks, jon