From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx198.postini.com [74.125.245.198]) by kanga.kvack.org (Postfix) with SMTP id B2A0F6B0031 for ; Thu, 25 Jul 2013 03:29:43 -0400 (EDT) Message-ID: <51F0D3CA.3080902@parallels.com> Date: Thu, 25 Jul 2013 11:29:14 +0400 From: Pavel Emelyanov MIME-Version: 1.0 Subject: Re: [PATCH] mm: Save soft-dirty bits on swapped pages References: <20130724163734.GE24851@moon> <20130724171728.GH8508@moon> <1374687373.7382.22.camel@dabdike> <20130724181516.GI8508@moon> <20130724185256.GA24365@moon> <51F0232D.6060306@parallels.com> <20130724190453.GJ8508@moon> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski , Cyrill Gorcunov Cc: James Bottomley , Linux MM , LKML , Andrew Morton , Matt Mackall , Xiao Guangrong , Marcelo Tosatti , KOSAKI Motohiro , Stephen Rothwell On 07/24/2013 11:40 PM, Andy Lutomirski wrote: > On Wed, Jul 24, 2013 at 12:04 PM, Cyrill Gorcunov wrote: >> On Wed, Jul 24, 2013 at 10:55:41PM +0400, Pavel Emelyanov wrote: >>>> >>>> Well, some part of information already lays in pte (such as 'file' bit, >>>> swap entries) so it looks natural i think to work on this level. but >>>> letme think if use page struct for that be more convenient... >>> >>> It hardly will be. Consider we have a page shared between two tasks, >>> then first one "touches" it and soft-dirty is put onto his PTE and, >>> subsequently, the page itself. The we go and clear sofr-dirty for the >>> 2nd task. What should we do with the soft-dirty bit on the page? >> >> Indeed, this won't help. Well then, bippidy-boppidy-boo, our >> pants are metaphorically on fire (c) > > Hmm. So there are at least three kinds of memory: > > Anonymous pages: soft-dirty works > Shared file-backed pages: soft-dirty does not work > Private file-backed pages: soft-dirty works (but see below) The shared file-backed pages case works, but unmap-map case doesn't preserve the soft-dirty bit. Just like the private file did. We'll fix this case next. > Perhaps another bit should be allocated to expose to userspace either > "soft-dirty", "soft-clean", or "soft-dirty unsupported"? > > There's another possible issue with private file-backed pages, though: > how do you distinguish clean-and-not-cowed from cowed-but-soft-clean? > (The former will reflect changes in the underlying file, I think, but > the latter won't.) There's a bit called PAGE_FILE bit in /proc/pagemap file introduced with the 052fb0d635df5d49dfc85687d94e1a87bf09378d commit. Plz, refer to Documentation/vm/pagemap.txt and soft-dirty.txt, all this is described there pretty well. > --Andy Thanks, Pavel -- 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