Re: lowmemory android driver not needed?

[KAMEZAWA Hiroyuki]

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