From mboxrd@z Thu Jan 1 00:00:00 1970 From: "prakash.sangappa" Subject: Re: [RFC PATCH] userfaultfd: Add feature to request for a signal delivery Date: Thu, 29 Jun 2017 14:49:01 -0700 Message-ID: <64c1f66e-95ca-7abb-6e22-44209ff7c73f@oracle.com> 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> <20170629104605.GA24911@rapoport-lnx> Reply-To: prakash.sangappa@oracle.com Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170629104605.GA24911@rapoport-lnx> Sender: owner-linux-mm@kvack.org To: Mike Rapoport Cc: Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , Mike Kravetz , Dave Hansen , Christoph Hellwig , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org On 06/29/2017 03:46 AM, Mike Rapoport wrote: > On Wed, Jun 28, 2017 at 11:23:32AM -0700, Prakash Sangappa wrote: [...] >> >> 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. > > Well, what I had in mind was using a single-process uffd monitor that will > track all the userfault file descriptors. With UFFD_EVENT_REMOVE this > process will know what areas are invalid and it will be able to process the > invalid access in any way it likes, e.g. send SIGBUS to the database > application. Use of a monitor process is also an overhead for the database. > > If you mmap() and userfaultfd_register() only at the initialization time, > it might be also possible to avoid sending userfault file descriptors to > the monitor process with UFFD_FEATURE_EVENT_FORK. The new processes are always exec'd in the database case and these processes could be mapping different files. So, not sure if UFFD_FEATURE_EVENT_FORK will be useful. Also, it may not be one process spawning the other new processes. > > -- > Sincerely yours, > Mike. > -- 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