From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Mon, 27 Jul 2015 16:04:05 +0200 (CEST) Received: from mail-wi0-f171.google.com ([209.85.212.171]:35180 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S27011327AbbG0OEDvp1Td (ORCPT ); Mon, 27 Jul 2015 16:04:03 +0200 Received: by wibxm9 with SMTP id xm9so114294750wib.0 for ; Mon, 27 Jul 2015 07:03:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-type:content-disposition:in-reply-to :user-agent; bh=NVtlRwEH+9fXuOZWWkQAoqqSwJSMJwMXMF4EIN9MwiI=; b=aRF5Op7Nz54O6tcI8Qe2ScPuKUQPdN+bHjy8Uv6S9aNSkpBamkTm5aD3L+KxYmVG9e 4Y1rlDobk/guzcbtLCZZtjqUHS4iBehR8SsUbPDuEwqaQa71Zv9ehkb3/W90hlvKrahp SjDARfKW0qorH/URZijCTJ5p4ASYohnAc0FWUYeGxTYX9VIvjvqTgGBx/Rkn24SlQOZB 10i4ccgb3hAJP/tehXUtfcmWtwlyLeKBSf8XaaHY/zcMo+o17nsbRpdPcUgqtGFNwmQa ngSEdLEjTOQ671Ly7434BGhdB2V1/bYMTAOg5oTf8WGM2tDbElcCGX45oJN4QDXY9OYb whmQ== X-Gm-Message-State: ALoCoQl32TpxY+PT2vbXqw5Vr1aQsQiBBE9iTuo8hxRcXPDFOddSpEU5v+lRTpjiRe/DxIUm2+nT X-Received: by 10.194.60.131 with SMTP id h3mr54229573wjr.156.1438005838509; Mon, 27 Jul 2015 07:03:58 -0700 (PDT) Received: from node.shutemov.name (dsl-espbrasgw1-54f9d4-72.dhcp.inet.fi. [84.249.212.72]) by smtp.gmail.com with ESMTPSA id ib9sm28122090wjb.2.2015.07.27.07.03.56 (version=TLSv1.2 cipher=AES128-GCM-SHA256 bits=128/128); Mon, 27 Jul 2015 07:03:57 -0700 (PDT) Received: by node.shutemov.name (Postfix, from userid 1000) id 937B866C9FA3; Mon, 27 Jul 2015 17:03:55 +0300 (EEST) Date: Mon, 27 Jul 2015 17:03:55 +0300 From: "Kirill A. Shutemov" 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 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> User-Agent: Mutt/1.5.23.1 (2014-03-12) 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: 48446 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: kirill@shutemov.name 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 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