Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753468AbdF2VkM (ORCPT ); Thu, 29 Jun 2017 17:40:12 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:17599 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752454AbdF2VkK (ORCPT ); Thu, 29 Jun 2017 17:40:10 -0400 Reply-To: prakash.sangappa@oracle.com Subject: Re: [RFC PATCH] userfaultfd: Add feature to request for a signal delivery References: <9363561f-a9cd-7ab6-9c11-ab9a99dc89f1@oracle.com> <20170627070643.GA28078@dhcp22.suse.cz> <20170627153557.GB10091@rapoport-lnx> <51508e99-d2dd-894f-8d8a-678e3747c1ee@oracle.com> <20170628131806.GD10091@rapoport-lnx> <3a8e0042-4c49-3ec8-c59f-9036f8e54621@oracle.com> <20170629080910.GC31603@dhcp22.suse.cz> To: Michal Hocko Cc: Mike Rapoport , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , Mike Kravetz , Dave Hansen , Christoph Hellwig , linux-api@vger.kernel.org From: "prakash.sangappa" Message-ID: <936bde7b-1913-5589-22f4-9bbfdb6a8dd5@oracle.com> Date: Thu, 29 Jun 2017 14:41:22 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <20170629080910.GC31603@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1239 Lines: 28 On 06/29/2017 01:09 AM, Michal Hocko wrote: > On Wed 28-06-17 11:23:32, Prakash Sangappa wrote: >> >> On 6/28/17 6:18 AM, Mike Rapoport wrote: > [...] >>> I've just been thinking that maybe it would be possible to use >>> UFFD_EVENT_REMOVE for this case. We anyway need to implement the generation >>> of UFFD_EVENT_REMOVE for the case of hole punching in hugetlbfs for >>> non-cooperative userfaultfd. It could be that it will solve your issue as >>> well. >>> >> Will this result in a signal delivery? >> >> In the use case described, the database application does not need any event >> for hole punching. Basically, just a signal for any invalid access to >> mapped area over holes in the file. > OK, but it would be better to think that through for other potential > usecases so that this doesn't end up as a single hugetlb feature. E.g. > what should happen if a regular anonymous memory gets swapped out? > Should we deliver signal as well? How does userspace tell whether this > was a no backing page from unavailable backing page? This may not be useful in all cases. Potential, it could be used with use of mlock() on anonymous memory to ensure any access to memory that is not locked is caught, again for robustness purpose.