From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id C4FD66B0087 for ; Thu, 18 Nov 2010 06:03:13 -0500 (EST) Received: from wpaz9.hot.corp.google.com (wpaz9.hot.corp.google.com [172.24.198.73]) by smtp-out.google.com with ESMTP id oAIB38qA007232 for ; Thu, 18 Nov 2010 03:03:08 -0800 Received: from ywa6 (ywa6.prod.google.com [10.192.1.6]) by wpaz9.hot.corp.google.com with ESMTP id oAIB37iA008059 for ; Thu, 18 Nov 2010 03:03:07 -0800 Received: by ywa6 with SMTP id 6so2379585ywa.40 for ; Thu, 18 Nov 2010 03:03:07 -0800 (PST) Date: Thu, 18 Nov 2010 03:03:01 -0800 From: Michel Lespinasse Subject: Re: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback Message-ID: <20101118110301.GA16625@google.com> References: <1289996638-21439-1-git-send-email-walken@google.com> <1289996638-21439-4-git-send-email-walken@google.com> <20101117125756.GA5576@amd> <1290007734.2109.941.camel@laptop> <20101117231143.GQ22876@dastard> <20101117235230.GL3290@thunk.org> <20101117165309.fa859fd3.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101117165309.fa859fd3.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: Ted Ts'o , Dave Chinner , Peter Zijlstra , Nick Piggin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Rik van Riel , Kosaki Motohiro , Theodore Tso , Michael Rubin , Suleiman Souhlal List-ID: On Wed, Nov 17, 2010 at 04:53:09PM -0800, Andrew Morton wrote: > On Wed, 17 Nov 2010 18:52:30 -0500 > "Ted Ts'o" wrote: > > > On Thu, Nov 18, 2010 at 10:11:43AM +1100, Dave Chinner wrote: > > > I don't think ->page_mkwrite can be worked around - we need that to > > > be called on the first write fault of any mmap()d page to ensure it > > > is set up correctly for writeback. If we don't get write faults > > > after the page is mlock()d, then we need the ->page_mkwrite() call > > > during the mlock() call. > > > > OK, so I'm not an mm hacker, so maybe I'm missing something. Could > > part of this be fixed by simply sending the write faults for > > mlock()'ed pages, so page_mkwrite() gets called when the page is > > dirtied. Seems like a real waste to have the file system pre-allocate > > all of the blocks for a mlock()'ed region. Why does mlock() have to > > result in the write faults getting suppressed when the page is > > actually dirtied? This is actually what the patch does - by having mlock() use a read fault, pages are loaded in memory and mlocked, but the ptes are not marked as writable so that a later write access will be caught as a write fault at that time (with all the usual dirtying and page_mkwrite() callbacks). > Yup, I don't think it would be too bad to take a minor fault each time > an mlocked page transitions from clean->dirty. > > In fact we should already be doing that, after the mlocked page gets > written back by kupdate? Hope so! Yes, handle_mm_fault() is careful to never create writable ptes pointing to clean file pages, so that a later write fault will correctly dirty the corresponding page. -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org