linux-kernel - Re: [PATCH 3/4] Staging: zram: allow partial page operations

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Date:	Mon, 13 Jun 2011 11:42:17 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Nitin Gupta <ngupta@...are.org>
CC:	Greg Kroah-Hartman <gregkh@...e.de>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 3/4] Staging: zram: allow partial page operations

On 06/10/2011 06:41 PM, Nitin Gupta wrote:
> On 06/10/2011 06:28 AM, Jerome Marchand wrote:
>> Commit 7b19b8d45b216ff3186f066b31937bdbde066f08 (zram: Prevent overflow
>> in logical block size) introduced ZRAM_LOGICAL_BLOCK_SIZE constant to
>> prevent overflow of logical block size on 64k page kernel.
>> However, the current implementation of zram only allow operation on block
>> of the same size as a page. That makes theorically legit 4k requests fail
>> on 64k page kernel.
>>
>> This patch makes zram allow operation on partial pages. Basically, it
>> means we still do operations on full pages internally, but only copy the
>> relevent segments from/to the user memory.
>>
> 
> Couldn't we just change struct queue_limits.logical_block_size type to 
> unsigned int or something so it could hold value of 64K? Then we could
> avoid making all these changes to handle partial page requests.
> 
> Thanks,
> Nitin

I believe logical_block_size is meant to be small. I don't know if it is
reasonable to set it to such a big value as 64k. I CCed Jens and Martin to
have a more valuable opinion on the matter.

Regards,
Jerome
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