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

From: Boaz Harrosh <bharrosh@panasas.com>
To: Christoph Hellwig <hch@lst.de>
Cc: James Bottomley <James.Bottomley@suse.de>,
	Mike Snitzer <snitzer@redhat.com>,
	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
Date: Wed, 30 Jun 2010 13:57:28 +0300	[thread overview]
Message-ID: <4C2B2318.1030107@panasas.com> (raw)
In-Reply-To: <20100630104155.GA1370@lst.de>

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?

But don't mind me, I'm just babbling. Not that I'll do anything about it.
Boaz