From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: about TRIM/DISCARD support and barriers Date: Mon, 24 Nov 2008 07:52:56 +0900 Message-ID: <1227480776.25499.3.camel@localhost.localdomain> References: <4928E010.4090801@kernel.org> <4929023C.2060302@suse.de> <20081123123514.GI5707@parisc-linux.org> <1227447584.4901.405.camel@macbook.infradead.org> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from accolon.hansenpartnership.com ([76.243.235.52]:49205 "EHLO accolon.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750818AbYKWWxI (ORCPT ); Sun, 23 Nov 2008 17:53:08 -0500 In-Reply-To: <1227447584.4901.405.camel@macbook.infradead.org> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: David Woodhouse Cc: Matthew Wilcox , Tejun Heo , Linux Kernel Mailing List , Nick Piggin , Jens Axboe , IDE/ATA development list , Jeff Garzik , Dongjun Shin , chris.mason@oracle.com On Sun, 2008-11-23 at 13:39 +0000, David Woodhouse wrote: > > We don't attempt to put non-contiguous ranges into a single TRIM yet. > > We don't even merge contiguous ranges -- I still need to fix the > elevators to stop writes crossing writes, I don't think we want to do that ... it's legal if the write isn't a barrier and it will inhibit merging. That may be just fine for a SSD, but it's not for spinning media since they get better performance out of merged writes. > before we can stop discards > from also being barriers. (Discards are just writes, for the purpose of > that conversation). Perhaps they shouldn't be ... they have different characteristics. For instance, a discard may cross a read or write that has no sectors in common with it; a discard may be merged as a non contiguous range (assuming the drive supports multiple ranges), etc. I think it might be better to give it its own type for the elevators. James