Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759659Ab1EBOi6 (ORCPT ); Mon, 2 May 2011 10:38:58 -0400 Received: from rcsinet10.oracle.com ([148.87.113.121]:16410 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756136Ab1EBOiw (ORCPT ); Mon, 2 May 2011 10:38:52 -0400 To: Lukas Czerner Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Dmitry Monakhov , Jens Axboe Subject: Re: [PATCH 3/3] blkdev: honor discard_granularity in blkdev_issue_discard() From: "Martin K. Petersen" Organization: Oracle References: <1304345841-20063-1-git-send-email-lczerner@redhat.com> <1304345841-20063-3-git-send-email-lczerner@redhat.com> Date: Mon, 02 May 2011 10:38:38 -0400 In-Reply-To: <1304345841-20063-3-git-send-email-lczerner@redhat.com> (Lukas Czerner's message of "Mon, 2 May 2011 16:17:21 +0200") Message-ID: User-Agent: Gnus/5.110013 (No Gnus v0.13) Emacs/23.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Source-IP: acsinet22.oracle.com [141.146.126.238] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090208.4DBEC1F9.00B6:SCFMA922111,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1264 Lines: 27 >>>>> "Lukas" == Lukas Czerner writes: Lukas> As Jeff Moyer pointed out we do not honor discard granularity Lukas> while submitting REQ_DISCARD bios of size smaller than Lukas> max_discard_sectors. That fact might have unwanted consequences Lukas> of device ignoring the request, or even worse if device firmware Lukas> is buggy. We've discussed this before and the consensus was not to do it. The granularity is a hint, not a hard limit like max_discard_sectors. We want the reporting to be comprehensive throughout the block layer. If we start aligning to the granularity at the top we lose information for stacked devices below with a finer granularity. So if we were to align to the granularity we'd want to do it at the bottom of the stack when we issue the command to the device. We've had a few proposed patches to did that but so far we've only found one device where it made a difference. And that case didn't justify adding a quirk. -- Martin K. Petersen Oracle Linux Engineering -- 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/