Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754747AbbHXNus (ORCPT ); Mon, 24 Aug 2015 09:50:48 -0400 Received: from mail-la0-f52.google.com ([209.85.215.52]:34807 "EHLO mail-la0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754137AbbHXNuq (ORCPT ); Mon, 24 Aug 2015 09:50:46 -0400 MIME-Version: 1.0 In-Reply-To: <55DB1C77.8070705@suse.cz> References: <1439097776-27695-1-git-send-email-emunson@akamai.com> <1439097776-27695-4-git-send-email-emunson@akamai.com> <20150812115909.GA5182@dhcp22.suse.cz> <20150819213345.GB4536@akamai.com> <20150820075611.GD4780@dhcp22.suse.cz> <20150820170309.GA11557@akamai.com> <20150821072552.GF23723@dhcp22.suse.cz> <20150821183132.GA12835@akamai.com> <55DB1C77.8070705@suse.cz> Date: Mon, 24 Aug 2015 16:50:44 +0300 Message-ID: Subject: Re: [PATCH v7 3/6] mm: Introduce VM_LOCKONFAULT From: Konstantin Khlebnikov To: Vlastimil Babka Cc: Eric B Munson , Michal Hocko , Andrew Morton , Jonathan Corbet , "Kirill A. Shutemov" , Linux Kernel Mailing List , dri-devel , "linux-mm@kvack.org" , Linux API Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1962 Lines: 49 On Mon, Aug 24, 2015 at 4:30 PM, Vlastimil Babka wrote: > On 08/24/2015 12:17 PM, Konstantin Khlebnikov wrote: >>> >>> >>> I am in the middle of implementing lock on fault this way, but I cannot >>> see how we will hanlde mremap of a lock on fault region. Say we have >>> the following: >>> >>> addr = mmap(len, MAP_ANONYMOUS, ...); >>> mlock(addr, len, MLOCK_ONFAULT); >>> ... >>> mremap(addr, len, 2 * len, ...) >>> >>> There is no way for mremap to know that the area being remapped was lock >>> on fault so it will be locked and prefaulted by remap. How can we avoid >>> this without tracking per vma if it was locked with lock or lock on >>> fault? >> >> >> remap can count filled ptes and prefault only completely populated areas. > > > Does (and should) mremap really prefault non-present pages? Shouldn't it > just prepare the page tables and that's it? As I see mremap prefaults pages when it extends mlocked area. Also quote from manpage : If the memory segment specified by old_address and old_size is locked : (using mlock(2) or similar), then this lock is maintained when the segment is : resized and/or relocated. As a consequence, the amount of memory locked : by the process may change. > >> There might be a problem after failed populate: remap will handle them >> as lock on fault. In this case we can fill ptes with swap-like non-present >> entries to remember that fact and count them as should-be-locked pages. > > > I don't think we should strive to have mremap try to fix the inherent > unreliability of mmap (MAP_POPULATE)? I don't think so. MAP_POPULATE works only when mmap happens. Flag MREMAP_POPULATE might be a good idea. Just for symmetry. -- 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/