From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 15 Mar 2017 20:48:09 +0100 (CET) Received: from 216-197-64-233.tingfiber.com ([216.197.64.233]:33324 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S23992100AbdCOTsDMH2aL (ORCPT ); Wed, 15 Mar 2017 20:48:03 +0100 Received: from dalias by brightrain.aerifal.cx with local (Exim 3.15 #2) id 1coEtH-0002WY-00; Wed, 15 Mar 2017 19:47:23 +0000 Date: Wed, 15 Mar 2017 15:47:23 -0400 From: Rich Felker To: Andy Lutomirski , Andy Lutomirski , Till Smejkal , Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Russell King , Catalin Marinas , Will Deacon , Steven Miao , Richard Kuo , Tony Luck , Fenghua Yu , James Hogan , Ralf Baechle , "James E.J. Bottomley" , Helge Deller , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Martin Schwidefsky , Heiko Carstens , Yoshinori Sato , "David S. Miller" , Chris Metcalf , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , X86 ML , Chris Zankel , Max Filippov , Arnd Bergmann , Greg Kroah-Hartman , Laurent Pinchart , Mauro Carvalho Chehab , Pawel Osciak , Marek Szyprowski , Kyungmin Park , David Woodhouse , Brian Norris , Boris Brezillon , Marek Vasut , Richard Weinberger , Cyrille Pitchen , Felipe Balbi , Alexander Viro , Benjamin LaHaise , Nadia Yvette Chambers , Jeff Layton , "J. Bruce Fields" , Peter Zijlstra , Hugh Dickins , Arnaldo Carvalho de Melo , Alexander Shishkin , Jaroslav Kysela , Takashi Iwai , "linux-kernel@vger.kernel.org" , linux-alpha@vger.kernel.org, arcml , "linux-arm-kernel@lists.infradead.org" , adi-buildroot-devel@lists.sourceforge.net, linux-hexagon@vger.kernel.org, "linux-ia64@vger.kernel.org" , linux-metag@vger.kernel.org, Linux MIPS Mailing List , linux-parisc@vger.kernel.org, linuxppc-dev , "linux-s390@vger.kernel.org" , "linux-sh@vger.kernel.org" , sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, Linux Media Mailing List , linux-mtd@lists.infradead.org, USB list , Linux FS Devel , linux-aio@kvack.org, "linux-mm@kvack.org" , Linux API , linux-arch , ALSA development Subject: Re: [RFC PATCH 00/13] Introduce first class virtual address spaces Message-ID: <20170315194723.GJ1693@brightrain.aerifal.cx> References: <20170315194447.scsf3fiwvf7z5gzc@arch-dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170315194447.scsf3fiwvf7z5gzc@arch-dev> User-Agent: Mutt/1.5.21 (2010-09-15) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 57305 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: dalias@libc.org Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Wed, Mar 15, 2017 at 12:44:47PM -0700, Till Smejkal wrote: > On Wed, 15 Mar 2017, Andy Lutomirski wrote: > > > One advantage of VAS segments is that they can be globally queried by user programs > > > which means that VAS segments can be shared by applications that not necessarily have > > > to be related. If I am not mistaken, MAP_SHARED of pure in memory data will only work > > > if the tasks that share the memory region are related (aka. have a common parent that > > > initialized the shared mapping). Otherwise, the shared mapping have to be backed by a > > > file. > > > > What's wrong with memfd_create()? > > > > > VAS segments on the other side allow sharing of pure in memory data by > > > arbitrary related tasks without the need of a file. This becomes especially > > > interesting if one combines VAS segments with non-volatile memory since one can keep > > > data structures in the NVM and still be able to share them between multiple tasks. > > > > What's wrong with regular mmap? > > I never wanted to say that there is something wrong with regular mmap. We just > figured that with VAS segments you could remove the need to mmap your shared data but > instead can keep everything purely in memory. > > Unfortunately, I am not at full speed with memfds. Is my understanding correct that > if the last user of such a file descriptor closes it, the corresponding memory is > freed? Accordingly, memfd cannot be used to keep data in memory while no program is > currently using it, can it? To be able to do this you need again some representation I have a name for application-allocated kernel resources that persist without a process holding a reference to them or a node in the filesystem: a bug. See: sysvipc. Rich From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 216-197-64-233.tingfiber.com ([216.197.64.233]:33324 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S23992100AbdCOTsDMH2aL (ORCPT ); Wed, 15 Mar 2017 20:48:03 +0100 Date: Wed, 15 Mar 2017 15:47:23 -0400 From: Rich Felker Subject: Re: [RFC PATCH 00/13] Introduce first class virtual address spaces Message-ID: <20170315194723.GJ1693@brightrain.aerifal.cx> References: <20170315194447.scsf3fiwvf7z5gzc@arch-dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170315194447.scsf3fiwvf7z5gzc@arch-dev> Return-Path: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Andy Lutomirski , Andy Lutomirski , Till Smejkal , Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Russell King , Catalin Marinas , Will Deacon , Steven Miao , Richard Kuo , Tony Luck , Fenghua Yu , James Hogan , Ralf Baechle , "James E.J. Bottomley" , Helge Deller , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Martin Schwidefsky , Heiko Carstens , Yoshinori Sato , "David S. Miller" , Chris Metcalf , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , X86 ML , Chris Zankel , Max Filippov , Arnd Bergmann , Greg Kroah-Hartman , Laurent Pinchart , Mauro Carvalho Chehab , Pawel Osciak , Marek Szyprowski , Kyungmin Park , David Woodhouse , Brian Norris , Boris Brezillon , Marek Vasut , Richard Weinberger , Cyrille Pitchen , Felipe Balbi , Alexander Viro , Benjamin LaHaise , Nadia Yvette Chambers , Jeff Layton , "J. Bruce Fields" , Peter Zijlstra , Hugh Dickins , Arnaldo Carvalho de Melo , Alexander Shishkin , Jaroslav Kysela , Takashi Iwai , "linux-kernel@vger.kernel.org" , linux-alpha@vger.kernel.org, arcml , "linux-arm-kernel@lists.infradead.org" , adi-buildroot-devel@lists.sourceforge.net, linux-hexagon@vger.kernel.org, "linux-ia64@vger.kernel.org" , linux-metag@vger.kernel.org, Linux MIPS Mailing List , linux-parisc@vger.kernel.org, linuxppc-dev , "linux-s390@vger.kernel.org" , "linux-sh@vger.kernel.org" , sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, Linux Media Mailing List , linux-mtd@lists.infradead.org, USB list , Linux FS Devel , linux-aio@kvack.org, "linux-mm@kvack.org" , Linux API , linux-arch , ALSA development Message-ID: <20170315194723.yFIMaQDr42bXlkwu2RMXllUp9tNtdhg-uC60gCty3q4@z> On Wed, Mar 15, 2017 at 12:44:47PM -0700, Till Smejkal wrote: > On Wed, 15 Mar 2017, Andy Lutomirski wrote: > > > One advantage of VAS segments is that they can be globally queried by user programs > > > which means that VAS segments can be shared by applications that not necessarily have > > > to be related. If I am not mistaken, MAP_SHARED of pure in memory data will only work > > > if the tasks that share the memory region are related (aka. have a common parent that > > > initialized the shared mapping). Otherwise, the shared mapping have to be backed by a > > > file. > > > > What's wrong with memfd_create()? > > > > > VAS segments on the other side allow sharing of pure in memory data by > > > arbitrary related tasks without the need of a file. This becomes especially > > > interesting if one combines VAS segments with non-volatile memory since one can keep > > > data structures in the NVM and still be able to share them between multiple tasks. > > > > What's wrong with regular mmap? > > I never wanted to say that there is something wrong with regular mmap. We just > figured that with VAS segments you could remove the need to mmap your shared data but > instead can keep everything purely in memory. > > Unfortunately, I am not at full speed with memfds. Is my understanding correct that > if the last user of such a file descriptor closes it, the corresponding memory is > freed? Accordingly, memfd cannot be used to keep data in memory while no program is > currently using it, can it? To be able to do this you need again some representation I have a name for application-allocated kernel resources that persist without a process holding a reference to them or a node in the filesystem: a bug. See: sysvipc. Rich