On Thu, 3 Dec 2009 13:58:05 +0900
Daisuke Nishimura [off-list ref] wrote:

I'm now trying to decrease these overhead as much as possible, and the current
status is bellow.

thanks.

(support for moving swap charge has not been pushed yet in my tree, so I tested
only (1) and (2) cases.)

       |  252M  |  512M  |   1G
  -----+--------+--------+--------
   (1) |  0.20  |  0.40  |  0.81
  -----+--------+--------+--------
   (2) |  0.20  |  0.40  |  0.81

What is the unit of each numbers ? seconds ? And migration of a process with 1G bytes
requires 0.8sec ? But, hmm, speed up twice! sounds nice.

What I've done are are:
- Instead of calling res_counter_uncharge() against the old cgroup in __mem_cgroup_move_account()
  evrytime, call res_counter_uncharge(PAGE_SIZE * moved) at the end of task migration once.

sounds reasonable.

- Instead of calling try_charge repeatedly, call res_counter_charge(PAGE_SIZE * necessary)
  in can_attach() if possible.

sounds reasonable, too.

- Not only res_counter_charge/uncharge, consolidate css_get()/put() too.

please do. But, hmm, I'd like to remove css_put/get per pages ;) But I put it aside now.

BTW, KAMEZAWA-san, are you planning to add mm_counter for swap yet ?

yes. please see my newest patch ;) extreme one.http://marc.info/?l=linux-mm&m=125980393923228&w=2

To tell the truth, instead of making use of mm_counter, I want to parse the page table
in can_attach as I did before, because:
- parsing the page table in can_attach seems not to add so big overheads(see below).

ok.

- if we add support for file-cache and shmem in future, I think we need to parse the page table
  anyway, because there is no independent mm_counter for shmem. I want to treat them
  independently because users don't consider shmem as file-cahce, IMHO.

ok. about scanning page tables. 
Moving 1G means moving 262144, scanning 128 page tables. Maybe not very big cost.

I still doubt moving "shared" pages "silently" is useful but it's another topic, here.

(parsing the page table in can_attach)
       |  252M  |  512M  |   1G
  -----+--------+--------+--------
   (1) |  0.21  |  0.41  |  0.83
  -----+--------+--------+--------
   (2) |  0.21  |  0.41  |  0.83

Hopefully, I want to post a new version in this week.

Thank you for your efforts.

Thanks,
-Kame


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