Re: [PATCH -mmotm 4/5] memcg: avoid oom during recharge at task move

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Thu, 3 Dec 2009 13:58:05 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> 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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