linux-ext4 - Re: [PATCH V2 0/7] Cleancache (was Transcendent Memory): overview

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Message-Id: <3721BEE2-DF2D-452A-8F01-E690E32C6B33@oracle.com>
Date:	Wed, 2 Jun 2010 22:53:44 -0600
From:	Andreas Dilger <andreas.dilger@...cle.com>
To:	ngupta@...are.org
Cc:	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Minchan Kim <minchan.kim@...il.com>, chris.mason@...cle.com,
	viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
	adilger@....com, tytso@....edu, mfasheh@...e.com,
	joel.becker@...cle.com, matthew@....cx,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	ocfs2-devel@....oracle.com, linux-mm@...ck.org, jeremy@...p.org,
	JBeulich@...ell.com, kurt.hackel@...cle.com, npiggin@...e.de,
	dave.mccracken@...cle.com, riel@...hat.com, avi@...hat.com,
	konrad.wilk@...cle.com
Subject: Re: [PATCH V2 0/7] Cleancache (was Transcendent Memory): overview

On 2010-06-02, at 20:46, Nitin Gupta wrote:
> On 06/03/2010 04:32 AM, Dan Magenheimer wrote:
>>> From: Minchan Kim [mailto:minchan.kim@...il.com]
>> 
>>>> I am also eagerly awaiting Nitin Gupta's cleancache backend
>>>> and implementation to do in-kernel page cache compression.
>>> 
>>> Do Nitin say he will make backend of cleancache for
>>> page cache compression?
>>> 
>>> It would be good feature.
>>> I have a interest, too. :)
>> 
>> That was Nitin's plan for his GSOC project when we last discussed
>> this.  Nitin is on the cc list and can comment if this has
>> changed.
> 
> Yes, I have just started work on in-kernel page cache compression
> backend for cleancache :)

Is there a design doc for this implementation?  I was thinking it would be quite clever to do compression in, say, 64kB or 128kB chunks in a mapping (to get decent compression) and then write these compressed chunks directly from the page cache to disk in btrfs and/or a revived compressed ext4.

That would mean that the on-disk compression algorithm needs to match the in-memory algorithm, which implies that the in-memory compression algorithm should be selectable on a per-mapping basis.

Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.

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