linux-kernel - Re: [PATCH v8 4/4] zram: promote zram from staging

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Date:	Wed, 4 Dec 2013 09:04:53 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Jens Axboe <axboe@...nel.dk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>, Bob Liu <bob.liu@...cle.com>,
	Luigi Semenzato <semenzato@...gle.com>,
	Pekka Enberg <penberg@...nel.org>, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH v8 4/4] zram: promote zram from staging

Hello Jerome,

On Tue, Dec 03, 2013 at 12:50:24PM +0100, Jerome Marchand wrote:
> On 11/25/2013 06:06 AM, Minchan Kim wrote:
> > Zram has lived in staging for a LONG LONG time and have been
> > fixed/improved by many contributors so code is clean and stable now.
> > Of course, there are lots of product using zram in real practice.
> > 
> > The major TV companys have used zram as swap since two years ago
> > and recently our production team released android smart phone with zram
> > which is used as swap, too and recently Android Kitkat start to use zram
> > for small memory smart phone.  And there was a report Google released
> > their ChromeOS with zram, too and cyanogenmod have been used zram
> > long time ago. And I heard some disto have used zram block device
> > for tmpfs. In addition, I saw many report from many other peoples.
> > For example, Lubuntu start to use it.
> > 
> > The benefit of zram is very clear. With my experience, one of the benefit
> > was to remove jitter of video application with backgroud memory pressure.
> > It would be effect of efficient memory usage by compression but more issue
> > is whether swap is there or not in the system. Recent mobile platforms have
> > used JAVA so there are many anonymous pages. But embedded system normally
> > are reluctant to use eMMC or SDCard as swap because there is wear-leveling
> > and latency issues so if we do not use swap, it means we can't reclaim
> > anoymous pages and at last, we could encounter OOM kill. :(
> > 
> > Although we have real storage as swap, it was a problem, too. Because
> > it sometime ends up making system very unresponsible caused by slow
> > swap storage performance.
> > 
> > Quote from Luigi on Google
> > "
> > Since Chrome OS was mentioned: the main reason why we don't use swap
> > to a disk (rotating or SSD) is because it doesn't degrade gracefully
> > and leads to a bad interactive experience.  Generally we prefer to
> > manage RAM at a higher level, by transparently killing and restarting
> > processes.  But we noticed that zram is fast enough to be competitive
> > with the latter, and it lets us make more efficient use of the
> > available RAM.
> > "
> > and he announced. http://www.spinics.net/lists/linux-mm/msg57717.html
> > 
> > Other uses case is to use zram for block device. Zram is block device
> > so anyone can format the block device and mount on it so some guys
> > on the internet start zram as /var/tmp.
> > http://forums.gentoo.org/viewtopic-t-838198-start-0.html
> > 
> > Let's promote zram and enhance/maintain it instead of removing.
> > 
> > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > Acked-by: Nitin Gupta <ngupta@...are.org>
> > Acked-by: Pekka Enberg <penberg@...nel.org>
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> > ---
> >  drivers/block/Kconfig           |    2 +
> >  drivers/block/Makefile          |    2 +
> >  drivers/block/zram/Kconfig      |   25 +
> >  drivers/block/zram/Makefile     |    3 +
> >  drivers/block/zram/zram.txt     |   77 +++
> 
> Shouldn't that go in Documentation/ directory?
> In Documentation/blockdev/ maybe.

Sure. I will wait more to get a review from others
and I will update it in next spin.

Thanks.

-- 
Kind regards,
Minchan Kim
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