From: Mark Lord Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation Date: Thu, 18 Nov 2010 17:07:02 -0500 Message-ID: <4CE5A386.7000105@teksavvy.com> References: <1290065809-3976-1-git-send-email-lczerner@redhat.com> <20101118130630.GJ6178@parisc-linux.org> <20101118134804.GN5618@dhcp231-156.rdu.redhat.com> <20101118141957.GK6178@parisc-linux.org> <20101118142918.GA18510@infradead.org> <1290100750.3041.72.camel@mulgrave.site> <1290102098.3041.77.camel@mulgrave.site> <4CE59E57.2090009@teksavvy.com> <1290117009.11007.42.camel@mulgrave.site> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Greg Freemyer , Jeff Moyer , Christoph Hellwig , Matthew Wilcox , Josef Bacik , Lukas Czerner , tytso@mit.edu, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, sandeen@redhat.com To: James Bottomley Return-path: Received: from ironport2-out.teksavvy.com ([206.248.154.181]:38304 "EHLO ironport2-out.pppoe.ca" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754952Ab0KRWHE (ORCPT ); Thu, 18 Nov 2010 17:07:04 -0500 In-Reply-To: <1290117009.11007.42.camel@mulgrave.site> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 10-11-18 04:50 PM, James Bottomley wrote: > > Before we go gung ho on this, there's no evidence that N discontiguous > ranges in one command are any better than the ranges sent N times ... > the same amount of erase overhead gets sent on SSDs. No, we do have evidence: execution time of the TRIM commands on the SSD. The one-range-at-a-time is incredibly slow compared to multiple ranges at a time. That slowness comes from somewhere, with about 99.9% certainty that it is due to the drive performing slow flash erase cycles. I think perhaps we should do the batching as much as possible, and then split them into single ranges for LLDs that cannot handle multi-ranges. Way more efficient that way. Cheers