From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030342AbXCFWHd (ORCPT ); Tue, 6 Mar 2007 17:07:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030357AbXCFWHd (ORCPT ); Tue, 6 Mar 2007 17:07:33 -0500 Received: from amsfep19-int.chello.nl ([213.46.243.16]:56188 "EHLO amsfep11-int.chello.nl" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1030342AbXCFWHc (ORCPT ); Tue, 6 Mar 2007 17:07:32 -0500 Subject: Re: [patch 2/8] update ctime and mtime for mmaped write From: Peter Zijlstra To: Miklos Szeredi Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, staubach@redhat.com, hugh@veritas.com In-Reply-To: <1173217621.4718.27.camel@lappy> References: <20070306180443.669036741@szeredi.hu> <20070306180549.312408559@szeredi.hu> <1173213151.4718.16.camel@lappy> <1173217621.4718.27.camel@lappy> Content-Type: text/plain Date: Tue, 06 Mar 2007 23:07:23 +0100 Message-Id: <1173218843.4718.38.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.8.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2007-03-06 at 22:47 +0100, Peter Zijlstra wrote: > On Tue, 2007-03-06 at 22:24 +0100, Miklos Szeredi wrote: > > > I'm not liking this, its not a constant operation as the name implies. > > > > OK, I'll think of something better. > > > > > And it style is a bit out of line with the rest of rmap. > > > > > > The thing it actually does is page_mkclean(), all it doesn't do is > > > setting the pte read-only. > > > > > > I can understand you wanting to avoid the overhead of the minor faults > > > resulting from using page_mkclean(), but I'm not sure its worth it. > > > > It would be nice if the cost of MS_ASYNC wouldn't be too high. And I > > do have the feeling that minor faults are far more expensive than > > cleaning the dirty bit in the ptes. > > > > Do you have any numbers? > > None what so ever, but I always think of msync as a rare function > (infrequent when compared to (minor) faults overall). But I don't have > numbers backing that up either. > > Also, the radix tree scan you do isn't exactly cheap either. > > So what I was wondering is whether its worth optimizing this at the cost > of another rmap walker. (one with very dubious semantics at that - it > clears the pte dirty bit but doesn't particularly care about that nor > does it respect the PG_dirty / PTE dirty relation) What this functionality requires is that MS_ASYNC is a full barrier wrt. dirtyness. That is, we want to call set_page_dirty_mappig() as soon as we touch a page in a dirtying fashion after MS_{,A}SYNC gets called. Hence we need the full page_mkclean() functionality, otherwise we don't set AS_CMTIME again in time.