From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlastimil Babka Subject: Re: [PATCH v7 3/6] mm: Introduce VM_LOCKONFAULT Date: Mon, 24 Aug 2015 15:30:31 +0200 Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: owner-linux-mm@kvack.org To: Konstantin Khlebnikov , Eric B Munson Cc: Michal Hocko , Andrew Morton , Jonathan Corbet , "Kirill A. Shutemov" , Linux Kernel Mailing List , dri-devel , "linux-mm@kvack.org" , Linux API List-Id: dri-devel@lists.freedesktop.org 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? > 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)? -- 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