linux-kernel - Re: [PATCH 0/8] zcache: page cache compression support

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Message-ID: <AANLkTim4t4zT5W0TJ7Vwzb568u1W6vz3b_cZirfK0Uhs@mail.gmail.com>
Date:	Thu, 20 Jan 2011 15:16:00 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Nitin Gupta <ngupta@...are.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>, Rik van Riel <riel@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Konrad Wilk <konrad.wilk@...cle.com>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/8] zcache: page cache compression support

Hi Christoph,

On Thu, Jan 20, 2011 at 07:33:29AM -0500, Nitin Gupta wrote:
>> I just started looking into kztmem (weird name!) but on
>> the high level it seems so much similar to zcache with some
>> dynamic resizing added (callback for shrinker interface).
>>
>> Now, I'll try rebuilding zcache according to new cleancache
>> API as provided by these set of patches. This will help refresh
>> whatever issues I was having back then with pagecache
>> compression and maybe pick useful bits/directions from
>> new kztmem work.

On Thu, Jan 20, 2011 at 2:47 PM, Christoph Hellwig <hch@...radead.org> wrote:
> Yes, we shouldn't have two drivers doing almost the same in the
> tree.  Also adding core hooks for staging drivers really is against
> the idea of staging of having a separate crap tree.  So it would be
> good to get zcache into a state where we can merge it into the
> proper tree first.  And then we can discuss if adding an abstraction
> layer between it and the core VM really makes sense, and if it does
> how.   But I'm pretty sure there's now need for multiple layers of
> abstraction for something that's relatively core VM functionality.
>
> E.g. the abstraction should involve because of it's users, not the
> compressed caching code should involve because it's needed to present
> a user for otherwise useless code.

I'm not sure which hooks you're referring to but for zcache we did this:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=b3a27d0529c6e5206f1b60f60263e3ecfd0d77cb

I completely agree with getting zcache merged properly before going
for the cleancache stuff.

                        Pekka
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