Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753898AbYCRN7j (ORCPT ); Tue, 18 Mar 2008 09:59:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752774AbYCRN7a (ORCPT ); Tue, 18 Mar 2008 09:59:30 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:33930 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752676AbYCRN7a (ORCPT ); Tue, 18 Mar 2008 09:59:30 -0400 Subject: Re: [patch 4/8] mm: allow not updating BDI stats in end_page_writeback() From: Peter Zijlstra To: Miklos Szeredi Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org In-Reply-To: References: <20080317191908.123631326@szeredi.hu> <20080317191945.122011759@szeredi.hu> <1205840031.8514.346.camel@twins> <1205843375.8514.357.camel@twins> <1205845702.8514.365.camel@twins> Content-Type: text/plain Date: Tue, 18 Mar 2008 14:59:20 +0100 Message-Id: <1205848760.8514.366.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.21.92 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1565 Lines: 33 On Tue, 2008-03-18 at 14:58 +0100, Miklos Szeredi wrote: > > > > So the thing that's in your way is that removing a page from the radix > > > > tree doesn't imply its done writing. So perhaps we should make that > > > > distinction instead? > > > > > > > > So instead of conditionally do part of the accounting, never do it and > > > > require something like: page_writeback_complete() to be called after a > > > > successfull test_clear_page_writeback(). > > > > > > Yes, that's a possibility, but then normal filesystems miss out on the > > > small optimization provided by doing the BDI accounting functions > > > inside the same IRQ disabled region as the radix tree operation. > > > Would that have any significant performance impact? > > > > Yeah, realized that. Don't know, would have to measure it somehow... > > some archs are rather slow with disabling IRQs, but we're talking about > > writeout which should be dominated by the IO times. > > > > Its just that your proposal exposes too much guts, I'd like the > > interface to be a little higher level. > > Well, but this is the kernel, you can't really make foolproof > interfaces. If we'll go with Andrew's suggestion, I'll add comments > warning users about not touching those flags unless they know what > they are doing, OK? Yeah, I guess so :-) -- 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/