linux-kernel - Re: [PATCH 1/2] block: fix leaks associated with discard request payload

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Date:	Wed, 30 Jun 2010 08:18:20 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Christoph Hellwig <hch@....de>,
	James Bottomley <James.Bottomley@...e.de>, axboe@...nel.dk,
	dm-devel@...hat.com, linux-kernel@...r.kernel.org,
	martin.petersen@...cle.com, akpm@...ux-foundation.org,
	linux-scsi@...r.kernel.org,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: Re: [PATCH 1/2] block: fix leaks associated with discard request
 payload

On Wed, Jun 30 2010 at  6:57am -0400,
Boaz Harrosh <bharrosh@...asas.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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