Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755748AbZICRw2 (ORCPT ); Thu, 3 Sep 2009 13:52:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753982AbZICRw1 (ORCPT ); Thu, 3 Sep 2009 13:52:27 -0400 Received: from casper.infradead.org ([85.118.1.10]:59800 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752853AbZICRw0 (ORCPT ); Thu, 3 Sep 2009 13:52:26 -0400 Subject: Re: [PATCH 1/7] Make DISCARD_BARRIER and DISCARD_NOBARRIER writes instead of reads From: David Woodhouse To: Christoph Hellwig Cc: linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, liml@rtr.ca, jens.axboe@oracle.com, matthew@wil.cx, Matthew Wilcox In-Reply-To: <20090829231121.144124147@bombadil.infradead.org> References: <20090829230332.017137693@bombadil.infradead.org> <20090829231121.144124147@bombadil.infradead.org> Content-Type: text/plain Date: Thu, 03 Sep 2009 18:52:20 +0100 Message-Id: <1252000340.4483.529.camel@macbook.infradead.org> Mime-Version: 1.0 X-Mailer: Evolution 2.26.3 (2.26.3-1.fc11) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1248 Lines: 29 On Sat, 2009-08-29 at 19:03 -0400, Christoph Hellwig wrote: > > The commands are conceptually writes, and in the case of IDE and SCSI > commands actually are writes. They were only reads because we thought > that would interact better with the elevators. Now the elevators know > about discard requests, that advantage no longer exists. Can you drop the final sentence of that? It isn't true, and I never said it. s/. Now.*/, but that isn't necessary, and making them writes makes it easier for the low-level IDE and SCSI code to cope with the fact that the command has to be sent with a payload./ The elevators _still_ don't know about discards, and will still let reads and writes (and discards, which are just a special case of writes) to the same sector all cross each other on the queue unless there's some external factor to prevent it. -- David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation -- 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/