linux-kernel - Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME

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Date:	Wed, 16 Jul 2014 14:45:46 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	James Bottomley <jbottomley@...allels.com>
Cc:	"martin.petersen\@oracle.com" <martin.petersen@...cle.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch\@infradead.org" <hch@...radead.org>,
	"devel\@linuxdriverproject.org" <devel@...uxdriverproject.org>,
	"apw\@canonical.com" <apw@...onical.com>,
	"kys\@microsoft.com" <kys@...rosoft.com>,
	"stable\@vger.kernel.org" <stable@...r.kernel.org>,
	"linux-scsi\@vger.kernel.org" <linux-scsi@...r.kernel.org>,
	"ohering\@suse.com" <ohering@...e.com>,
	"jasowang\@redhat.com" <jasowang@...hat.com>
Subject: Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16

>>>>> "James" == James Bottomley <jbottomley@...allels.com> writes:

>> 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.

James> Hang on ... unless we apply Christoph or my fix, we'll get the
James> same issue with every raid driver (that's about 10 I think) that
James> set no_write_same when they hit a >2TB RAID volume,

no_write_same is set for all the RAID controller drivers (54b2b50c20a6).

If a WRITE SAME(10/16) command fails and the UNMAP bit is not set we'll
set no_write_same=1 and disable REQ_WRITE_SAME support.

If a WRITE SAME(10/16) command fails and the UNMAP bit is set we'll
disable REQ_DISCARD support.

Not sure where the 10 vs. 16 byte 2TB limitation comes into play here?

-- 
Martin K. Petersen	Oracle Linux Engineering
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