linux-kernel - Re: [PATCH 1/3]: compressed RAM block device

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Date:	Wed, 18 Mar 2009 18:08:30 +0530
From:	Nitin Gupta <ngupta@...are.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3]: compressed RAM block device

Nick Piggin wrote:
> On Tuesday 17 March 2009 22:36:46 Nitin Gupta wrote:
>>   drivers/block/Kconfig     |   22 +
>>   drivers/block/Makefile    |    1 +
>>   drivers/block/compcache.c |  995
>> +++++++++++++++++++++++++++++++++++++++++++++ drivers/block/compcache.h | 
>> 160 ++++++++
>>   4 files changed, 1178 insertions(+), 0 deletions(-)
>>
>> Creates RAM based block device (ramzswap0) which can be used as swap
>> device. Pages swapped to this are compressed and stored in memory itself.
>>
>> The module is called compcache.ko. It depends on:
>>   - xvmalloc.ko: memory allocator
>>   - lzo_compress.ko
>>   - lzo_decompress.ko
>>
>> See Documentation/blockdev/compcache.txt for usage details.
>>
>> Project home: http://code.google.com/p/compcache/
> 

> I wonder how hard it would be to make the compression code
> use an arbitrary file or device for the storage backend rather
> than make a new block device? Then you could make a new ram
> block device that can swap its pages out (or even extend brd.c
> with that functionality, or use loop on tmpfs etc).
> 

Its already done as mentioned in Documentation/blockdev/compcache.txt
(patch 3/3) but I should have added it here also: compcache accepts
"backing_dev" parameter for backing swap partition - this allows us to
forward any R/W request to backing swap device. Currently only poorly
compressible pages (compress length > PAGE_SIZE/2) are forwarded to
backing_dev.

Thanks,
Nitin




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