Date: Wed, 30 Jun 2010 08:18:20 -0400
From: Mike Snitzer <snitzer@redhat.com>
To: Boaz Harrosh <bharrosh@panasas.com>
Cc: Christoph Hellwig <hch@lst.de>, James Bottomley <James.Bottomley@suse.de>,
       axboe@kernel.dk, dm-devel@redhat.com, linux-kernel@vger.kernel.org,
       martin.petersen@oracle.com, akpm@linux-foundation.org,
       linux-scsi@vger.kernel.org,
       FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Subject: Re: [PATCH 1/2] block: fix leaks associated with discard request
 payload
Message-ID: <20100630121820.GB22798@redhat.com>
References: <20100622180029.GA15950@redhat.com>
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 <1277652576.4366.19.camel@mulgrave.site>
 <4C2B012B.2000407@panasas.com>
 <20100630084204.GA27609@lst.de>
 <4C2B1B7D.2090607@panasas.com>
 <20100630104155.GA1370@lst.de>
 <4C2B2318.1030107@panasas.com>
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On Wed, Jun 30 2010 at  6:57am -0400,
Boaz Harrosh <bharrosh@panasas.com> wrote:

> On 06/30/2010 01:41 PM, Christoph Hellwig wrote:
> > On Wed, Jun 30, 2010 at 01:25:01PM +0300, Boaz Harrosh wrote:
> >> OK, Thanks, I see. Is it one of these operations, (like we have in OSD) where
> >> the CDB information spills into the payload? like the scatter-gather and extent
> >> lists and such.
> > 
> > For UNMAP the payload is a list of block number / length pairs, while
> > the CDB itself doesn't contain any information like that.  It's a rather
> > awkward command.
> > 
> 
> How big can that be? could we, maybe, use the sense_buffer, properly allocated
> already?
> 
> >> Do we actually use a WRITE_SAME which is not zero? for what use?
> > 
> > The kernel doesn't issue any WRITE SAME without the unmap bit set.
> 
> So if the unmap bit is set then the page can just be zero, right?
> 
> I still think a static zero-page is a worth while optimization. And
> block-drivers can take care with special needs with a private mem_pool
> or something. For the discard-type user and generic block layer the
> page is just an implementation specific residue, No?

Why should the block layer have any role in managing this page?  Block
layer doesn't care about it, SCSI does.

Mike
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