From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Nicholas A. Bellinger" Subject: Re: [PATCH 2/3] target: Add max_write_same_len device attribute Date: Thu, 15 Nov 2012 11:23:12 -0800 Message-ID: <1353007392.4447.22.camel@haakon2.linux-iscsi.org> References: <1352405238-23267-1-git-send-email-nab@linux-iscsi.org> <1352405238-23267-3-git-send-email-nab@linux-iscsi.org> <20121115105312.GC28956@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20121115105312.GC28956@infradead.org> Sender: linux-kernel-owner@vger.kernel.org To: Christoph Hellwig Cc: target-devel , linux-scsi , linux-kernel , Christoph Hellwig , "Martin K. Petersen" List-Id: linux-scsi@vger.kernel.org On Thu, 2012-11-15 at 05:53 -0500, Christoph Hellwig wrote: > On Thu, Nov 08, 2012 at 08:07:17PM +0000, Nicholas A. Bellinger wrote: > > From: Nicholas Bellinger > > > > This patch adds a new max_write_same_len device attribute for use with > > WRITE_SAME w/ UNMAP=0 backend emulation. > > > > Also, update block limits VPD emulation code in spc_emulate_evpd_b0() to > > set the default MAXIMUM WRITE SAME LENGTH value of zero. > > why do we need an exposed attribute for this? > This is useful for userspace to reduce the allowed maximum from the default 0xFFFF set by IBLOCK. Allowing huge WRITE_SAMEs can very much effect performance (esp. with spinning media), so being able to reduce the max we accept via a userspace tunable is helpful. --nab