Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753442AbcD1ACD (ORCPT ); Wed, 27 Apr 2016 20:02:03 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:33102 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752205AbcD1ACB (ORCPT ); Wed, 27 Apr 2016 20:02:01 -0400 To: Rafael David Tinoco Cc: Ben Hutchings , linux-kernel@vger.kernel.org, stable@vger.kernel.org, akpm@linux-foundation.org, Paolo Bonzini , "Martin K. Petersen" , Christoph Hellwig Subject: Re: [PATCH 3.16 106/217] sd: disable discard_zeroes_data for UNMAP From: "Martin K. Petersen" Organization: Oracle Corporation References: Date: Wed, 27 Apr 2016 20:01:36 -0400 In-Reply-To: (Rafael David Tinoco's message of "Wed, 27 Apr 2016 17:43:55 -0300") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 901 Lines: 19 >>>>> "Rafael" == Rafael David Tinoco writes: Rafael> It seems that changing discard method from UNMAP to WRITE Rafael> SAME(16) without using NDOB bit (as first described in Rafael> sbc3r35b.pdf) can cause performance problems on big discards Rafael> (since data-out buffer will be checked for every WRITE SAME Rafael> command). I think this is happening after this commit, since Rafael> NDOB bit wasn't implemented with this change (afaik, iirc). We don't currently use NDOB since there is no VPD parameter to key off of. I am also not aware of any devices that actually support it. I am working on some patches that changes how we submit write same and unmap down the stack to make it easier for the target subsystem to provide zeroing guarantees. Those changes will clean some of this up but they are 4.8 material. -- Martin K. Petersen Oracle Linux Engineering