Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752353Ab3GXSWK (ORCPT ); Wed, 24 Jul 2013 14:22:10 -0400 Received: from mail-vb0-f53.google.com ([209.85.212.53]:62260 "EHLO mail-vb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751222Ab3GXSWI (ORCPT ); Wed, 24 Jul 2013 14:22:08 -0400 MIME-Version: 1.0 In-Reply-To: <20130724181516.GI8508@moon> References: <20130724160826.GD24851@moon> <20130724163734.GE24851@moon> <20130724171728.GH8508@moon> <1374687373.7382.22.camel@dabdike> <20130724181516.GI8508@moon> From: Andy Lutomirski Date: Wed, 24 Jul 2013 11:21:46 -0700 Message-ID: Subject: Re: [PATCH] mm: Save soft-dirty bits on swapped pages To: Cyrill Gorcunov Cc: James Bottomley , Linux MM , LKML , Pavel Emelyanov , Andrew Morton , Matt Mackall , Xiao Guangrong , Marcelo Tosatti , KOSAKI Motohiro , Stephen Rothwell Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1976 Lines: 41 On Wed, Jul 24, 2013 at 11:15 AM, Cyrill Gorcunov wrote: > On Wed, Jul 24, 2013 at 10:42:24AM -0700, Andy Lutomirski wrote: >> > >> > Lets just be clear about the problem first: the vmscan pass referred to >> > above happens only on clean pages, so the soft dirty bit could only be >> > set if the page was previously dirty and got written back. Now it's an >> > exercise for the reader whether we want to reinstantiate a cleaned >> > evicted page for the purpose of doing an iterative migration or whether >> > we want to flip the page in the migrated entity to be evicted (so if it >> > gets referred to, it pulls in an up to date copy) ... assuming the >> > backing file also gets transferred, of course. > > Good question! I rather forward it to Pavel as an author for soft dirty > bit feature. Pavel? > >> I think I understand your distinction. Nonetheless, given the loss of >> the soft-dirty bit, the migration tool could fail to notice that the >> pages was dirtied and subsequently cleaned and evicted. I'm >> unconvinced that doing this on a per-PTE basis is the right way, >> though. > > I fear for tracking soft-dirty-bit for swapped entries we sinply have > no other place than pte (still i'm quite open for ideas, maybe there > are a better way which I've missed). I know approximately nothing about how swap and anon_vma work. For files, sticking it in struct page seems potentially nicer, although finding a free bit might be tough. (FWIW, I have plans to free up a page flag on x86 some time moderately soon as part of a completely unrelated project.) I think this stuff really belongs to the address_space more than it belongs to the pte. How do you handle the write syscall? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/