linux-kernel - Re: [PATCH V2 2/3] drivers/staging: zcache: host services and PAM services

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Message-ID: <4D533CB5.6060807@vflare.org>
Date:	Wed, 09 Feb 2011 20:17:41 -0500
From:	Nitin Gupta <ngupta@...are.org>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	Dan Magenheimer <dan.magenheimer@...cle.com>, gregkh@...e.de,
	Chris Mason <chris.mason@...cle.com>,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	matthew@....cx, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	jeremy@...p.org, Kurt Hackel <kurt.hackel@...cle.com>,
	npiggin@...nel.dk, riel@...hat.com,
	Konrad Wilk <konrad.wilk@...cle.com>, mel@....ul.ie,
	kosaki.motohiro@...fujitsu.com, sfr@...b.auug.org.au,
	wfg@...l.ustc.edu.cn, tytso@....edu, viro@...iv.linux.org.uk,
	hughd@...gle.com, hannes@...xchg.org
Subject: Re: [PATCH V2 2/3] drivers/staging: zcache: host services and PAM
 services

On 02/09/2011 06:46 PM, Minchan Kim wrote:
> Hi Nitin,
>
> Sorry for late response.
>
> On Thu, Feb 10, 2011 at 2:36 AM, Nitin Gupta<ngupta@...are.org>  wrote:
>> On 02/09/2011 11:39 AM, Dan Magenheimer wrote:
>>>
>>>
>>>> From: Minchan Kim [mailto:minchan.kim@...il.com]
>>>
>>>> As I read your comment, I can't find the benefit of zram compared to
>>>> frontswap.
>>>
>>> Well, I am biased, but I agree that frontswap is a better technical
>>> solution than zram. ;-)  But "dynamic-ity" is very important to
>>> me and may be less important to others.
>>>
>>
>>
>> I agree that frontswap is better than zram when considering swap as the use
>> case - no bio overhead, dynamic resizing. However, zram being a *generic*
>> block-device has some unique cases too like hosting files on /tmp, various
>> caches under /var or any place where a compressed in-memory block device can
>> help.
>
> Yes. I mentioned that benefit but I am not sure the reason is enough.
> What I had in mind long time ago is that zram's functionality into brd.
> So someone who want to compress contents could use it with some mount
> option to enable compression.
> By such way, many ramdisk user can turn it on easily.
> If many user begin using the brd, we can see many report about
> performance then solve brd performance s as well as zcache world-wide
> usage.
>
> Hmm,  the idea is too late?
>
>>
>> So, frontswap and zram have overlapping use case of swap but are not the
>> same.
>
> If we can insert zram's functionality into brd, maybe there is no
> reason to coexist.
>
>
>>

I thought about this before starting with zram development but thought 
adding compression (and in future, defrag) and use of custom allocator 
is just too much of a hassle and thus dropped the idea. If someone is 
anyhow interested in merging brd and zram I would be glad to help but I 
still think that is simply not worth the effort.

Thanks,
Nitin
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