Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935001AbaGPSpO (ORCPT ); Wed, 16 Jul 2014 14:45:14 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:30890 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934841AbaGPSpL convert rfc822-to-8bit (ORCPT ); Wed, 16 Jul 2014 14:45:11 -0400 From: "Elliott, Robert (Server Storage)" To: James Bottomley , "martin.petersen@oracle.com" CC: "linux-kernel@vger.kernel.org" , "hch@infradead.org" , "devel@linuxdriverproject.org" , "apw@canonical.com" , "kys@microsoft.com" , "stable@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "ohering@suse.com" , "jasowang@redhat.com" Subject: RE: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16 Thread-Topic: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16 Thread-Index: AQHPoR4GwAidebdDdkqVl4qxemzvp5ui/ekAgAABJhA= Date: Wed, 16 Jul 2014 18:43:43 +0000 Message-ID: <94D0CD8314A33A4D9D801C0FE68B402958BA721F@G9W0745.americas.hpqcorp.net> References: <20140709084300.GD6012@infradead.org> <1404935792.2184.5.camel@dabdike.int.hansenpartnership.com> <2f3ae589e6f149acbe4c5dd79f905971@BY2PR03MB299.namprd03.prod.outlook.com> <1404944843.2184.8.camel@dabdike.int.hansenpartnership.com> <20140711063216.GA20660@infradead.org> <328b7a6174ef4dd8a54a7db5ac959834@BY2PR03MB299.namprd03.prod.outlook.com> <20140716110111.GA7382@infradead.org> <20140716173827.GB20528@infradead.org> <1405533734.3165.12.camel@dabdike.int.hansenpartnership.com> In-Reply-To: <1405533734.3165.12.camel@dabdike.int.hansenpartnership.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [16.210.48.37] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: linux-scsi-owner@vger.kernel.org [mailto:linux-scsi- > owner@vger.kernel.org] On Behalf Of James Bottomley > Sent: Wednesday, 16 July, 2014 1:02 PM > To: martin.petersen@oracle.com > Cc: linux-kernel@vger.kernel.org; hch@infradead.org; > devel@linuxdriverproject.org; apw@canonical.com; kys@microsoft.com; > stable@vger.kernel.org; linux-scsi@vger.kernel.org; ohering@suse.com; > jasowang@redhat.com > Subject: Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16 > > On Wed, 2014-07-16 at 13:47 -0400, Martin K. Petersen wrote: > > >>>>> "Christoph" == hch@infradead org writes: > > > > Christoph> Oh, we actually have devices that support WRITE SAME with > > Christoph> unmap, but not without? That's defintively a little strange. > > > > Yep :( > > > > There were several SSDs that did not want to support wearing out flash > > by writing gobs of zeroes and only support the UNMAP case. > > > > Christoph> Yes, and it did this intentionally. I really wouldn't expect > > Christoph> devices to support WRITE SAME with UNMAP but blow up on a > > Christoph> WRITE SAME without it (and not just simple fail it in an > > Christoph> orderly way). > > > > *sigh* > > > > Christoph> It definitively seems odd to default to trying WRITE SAME for > > Christoph> unmap for a device that explicitly tells us that it doesn't > > Christoph> support WRITE SAME. > > > > Maybe it's just a naming thing. I was really trying to convey > > no_req_write_same support, not no_write_same_10_or_16. > > > > Christoph> Note that I'm not against your patch - I suspect forcing us > > Christoph> to read EVPD pages even for devices that claim to be SPC-2 > > Christoph> will come in useful in various scenarios. > > > > I don't have a problem with a BLIST_PREFER_UNMAP flag or something like > > that. But BLIST_TRY_VPD_PAGES seems more generally useful and it does > > fix the problem at hand. That's why I went that route. > > Hang on ... unless we apply Christoph or my fix, we'll get the same > issue with every raid driver (that's about 10 I think) that set > no_write_same when they hit a >2TB RAID volume, so I think we need both > fixes. > > James > WRITE SAME with the UNMAP bit set to one (and a few other conditions) guarantees that the data is zeroed out, while the UNMAP command is just a hint. They're not fully interchangeable. Which semantics are implied by REQ_DISCARD and these functions? One benefit of UNMAP is that UNMAP supports a list of discontiguous LBA ranges, whereas WRITE SAME just supports one LBA range. sd_setup_discard_cmnd is not taking advantage of this feature, though. Ideally, the block layer would merge multiple discards into one UNMAP command if they're stuck on the request queue for a while, like it merges adjacent reads and writes. That would pave the way for building up WRITE SCATTERED and READ GATHERED commands. -- 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/