From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kirill A. Shutemov" Subject: Re: [PATCH V5 5/7] mm: mmap: Add mmap flag to request VM_LOCKONFAULT Date: Mon, 27 Jul 2015 17:03:55 +0300 Message-ID: <20150727140355.GA11360@node.dhcp.inet.fi> References: <1437773325-8623-1-git-send-email-emunson@akamai.com> <1437773325-8623-6-git-send-email-emunson@akamai.com> <20150727073129.GE11657@node.dhcp.inet.fi> <20150727134126.GB17133@akamai.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150727134126.GB17133@akamai.com> 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: Eric B Munson Cc: Andrew Morton , Michal Hocko , Vlastimil Babka , Paul Gortmaker , Chris Metcalf , Guenter Roeck , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org List-Id: linux-arch.vger.kernel.org On Mon, Jul 27, 2015 at 09:41:26AM -0400, Eric B Munson wrote: > On Mon, 27 Jul 2015, Kirill A. Shutemov wrote: > > > On Fri, Jul 24, 2015 at 05:28:43PM -0400, Eric B Munson wrote: > > > The cost of faulting in all memory to be locked can be very high when > > > working with large mappings. If only portions of the mapping will be > > > used this can incur a high penalty for locking. > > > > > > Now that we have the new VMA flag for the locked but not present state, > > > expose it as an mmap option like MAP_LOCKED -> VM_LOCKED. > > > > As I mentioned before, I don't think this interface is justified. > > > > MAP_LOCKED has known issues[1]. The MAP_LOCKED problem is not necessary > > affects MAP_LOCKONFAULT, but still. > > > > Let's not add new interface unless it's demonstrably useful. > > > > [1] http://lkml.kernel.org/g/20150114095019.GC4706@dhcp22.suse.cz > > I understand and should have been more explicit. This patch is still > included becuase I have an internal user that wants to see it added. > The problem discussed in the thread you point out does not affect > MAP_LOCKONFAULT because we do not attempt to populate the region with > MAP_LOCKONFAULT. > > As I told Vlastimil, if this is a hard NAK with the patch I can work > with that. Otherwise I prefer it stays. That's not how it works. Once an ABI added to the kernel it stays there practically forever. Therefore it must be useful to justify maintenance cost. I don't see it demonstrated. So, NAK. -- Kirill A. Shutemov From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f180.google.com ([209.85.212.180]:36624 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754052AbbG0OEA (ORCPT ); Mon, 27 Jul 2015 10:04:00 -0400 Received: by wicgb10 with SMTP id gb10so113945007wic.1 for ; Mon, 27 Jul 2015 07:03:58 -0700 (PDT) Date: Mon, 27 Jul 2015 17:03:55 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH V5 5/7] mm: mmap: Add mmap flag to request VM_LOCKONFAULT Message-ID: <20150727140355.GA11360@node.dhcp.inet.fi> References: <1437773325-8623-1-git-send-email-emunson@akamai.com> <1437773325-8623-6-git-send-email-emunson@akamai.com> <20150727073129.GE11657@node.dhcp.inet.fi> <20150727134126.GB17133@akamai.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150727134126.GB17133@akamai.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Eric B Munson Cc: Andrew Morton , Michal Hocko , Vlastimil Babka , Paul Gortmaker , Chris Metcalf , Guenter Roeck , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org Message-ID: <20150727140355.mcOVz7tKSZDTxJCNhTCCn8TQs65D_e4iyXP8m3_SJuI@z> On Mon, Jul 27, 2015 at 09:41:26AM -0400, Eric B Munson wrote: > On Mon, 27 Jul 2015, Kirill A. Shutemov wrote: > > > On Fri, Jul 24, 2015 at 05:28:43PM -0400, Eric B Munson wrote: > > > The cost of faulting in all memory to be locked can be very high when > > > working with large mappings. If only portions of the mapping will be > > > used this can incur a high penalty for locking. > > > > > > Now that we have the new VMA flag for the locked but not present state, > > > expose it as an mmap option like MAP_LOCKED -> VM_LOCKED. > > > > As I mentioned before, I don't think this interface is justified. > > > > MAP_LOCKED has known issues[1]. The MAP_LOCKED problem is not necessary > > affects MAP_LOCKONFAULT, but still. > > > > Let's not add new interface unless it's demonstrably useful. > > > > [1] http://lkml.kernel.org/g/20150114095019.GC4706@dhcp22.suse.cz > > I understand and should have been more explicit. This patch is still > included becuase I have an internal user that wants to see it added. > The problem discussed in the thread you point out does not affect > MAP_LOCKONFAULT because we do not attempt to populate the region with > MAP_LOCKONFAULT. > > As I told Vlastimil, if this is a hard NAK with the patch I can work > with that. Otherwise I prefer it stays. That's not how it works. Once an ABI added to the kernel it stays there practically forever. Therefore it must be useful to justify maintenance cost. I don't see it demonstrated. So, NAK. -- Kirill A. Shutemov