On Wed, Mar 21, 2012 at 06:52:04PM +0900, KAMEZAWA Hiroyuki wrote:

As discussed before, I post this to fix the spec and implementation of task moving.
Then, do you think what target kernel version should be ? 3.4/3.5 ?
but yes, it may be late for 3.4....

==
In documentation, it's said that 'shared anon are not moved'.
But in implementation, the check was wrong.

  if (!move_anon() || page_mapcount(page) > 2)

Ah, memcg has been moving shared anon pages for a long time.

Then, here is a discussion about handling of shared anon pages.

 - It's complex
 - Now, shared file caches are moved in force.
 - It adds unclear check as page_mapcount(). To do correct check,
   we should check swap users, etc.
 - No one notice this implementation behavior. So, no one get benefit
   from the design.
 - In general, once task is moved to a cgroup for running, it will not
   be moved....
 - Finally, we have control knob as memory.move_charge_at_immigrate.

Here is a patch to allow moving shared pages, completely. This makes
memcg simpler and fix current broken code.

Note:
 IIUC, libcgroup's cgroup daemon moves tasks after exec().
 So, it's not affected.
 libcgroup's command "cgexec" does move itsef to a memcg and call exec()
 without fork(). it's not affected.

Changelog:
 - fixed PageAnon() check.
 - remove call of lookup_swap_cache()
 - fixed Documentation.

Suggested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: KAMEZAWA Hiroyuki <redacted>

It looks good to me.

Reviewed-by: Naoya Horiguchi <redacted>

Thanks,
Naoya

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