linux-kernel - Re: lowmemory android driver not needed?

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Message-Id: <20090121122952.18e4bb8c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 21 Jan 2009 12:29:52 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Greg KH <greg@...ah.com>, Paul Mundt <lethal@...ux-sh.org>,
	Trilok Soni <soni.trilok@...il.com>,
	Arve Hj?nnev?g <arve@...roid.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@...e.cz>,
	Brian Swetland <swetland@...gle.com>, arve@...gle.com,
	San Mehat <san@...roid.com>, Robert Love <rlove@...gle.com>,
	linux-kernel@...r.kernel.org,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	ext Juha Yrj?l? <juha.yrjola@...idboot.com>,
	viktor.rosendahl@...ia.com
Subject: Re: lowmemory android driver not needed?

On Wed, 21 Jan 2009 11:50:48 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> last year, I received many feedback from lkml folks and my article reader.
> (I monthly write kernel patch introduction article to japanese web
>  magazine and receive some feedback periodically)
> 
> I learned many people want flexibility notification.
> (per workload, per user, et al)
> eg. nokia lowmem driver have exception process defined by uid.
> 
> at top of last year, I thought memcg don't provide good infrastructure.
> the first version memcg is just pretty funny joke. if its config turn on,
> memory workload performance decrease ~30% although the user don't use 
> memcg at runtime. then nobody use it.
> but recently, KAMEZAWA hiroyuki (and Li zefan, Daisuke Nishimura et al)
> dramatically improvement memcg performance. 
> now, memcg overhead become less than 1%. 
                             ^^^^^^^^^^^^
just depends on workload...

> 
> Then, I think any memory accounting activity should use this infrastructure.
> That's my homework.
> 

But, memcg requires much memory to track usage of pages, a page_cgroup structure, 
40bytes per page on 64bit, 20bytes per page on 32bit.
Probably, for embeded people, this additinal memory usage is not acceptable.

Below is just a noise:
==
As my personal project, I'd like to write on-demand-fake-numa for generic archs.
Now, section size is 128MB on x86-64. I'd like to allow following ops.

  # create_new_node (echo node_number > /sys/device/system/node/add_fake_node)
  # offline memory (echo offline > /sys/device/system/memory/memoryXXX/state)
  # attach offlined memory to new node
                   (echo node_number > /sys/device/system/memory/memoryXXX/attach)
  # online memmory (echo online > /sys/device/system/memory/memoryXXX/state)

Then, memoryXXX (128MB of chunk of memory) is controlled under a new fake node
"node_number".

For embeded systems, you may be able to modify SECTION_SIZE smaller (8-16MB?) and
cpuset will give them enough resource isolation.
(But not so flexible as memory cgroup.)

you can use node+cpuset information to track memory usage by apps.

Note: OOM-Killer kills process within cpuset.

Thanks,
-Kame






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