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Re: [ckrm-tech] [PATCH 4/13] BC: context handling [message #8527 is a reply to message #8525]

Thu, 23 November 2006 08:35

Pavel Emelianov
Messages: 1149
Registered: September 2006

Senior Member

Paul Menage wrote:
> On 11/9/06, Kirill Korotaev <dev@sw.ru> wrote:
>> +
>> +int bc_task_move(int pid, struct beancounter *bc, int whole)
>> +{
>
> ...
>
>> +
>> + down_write(&mm->mmap_sem);
>> + err = stop_machine_run(do_set_bcid, &data, NR_CPUS);
>> + up_write(&mm->mmap_sem);
>
> Isn't this a little heavyweight for moving a task into/between
> beancounters?

It's a main reason we were against moving arbitrary task.

We need to track the situation when we change beancounter on
task that is currently handles an interrupt and thus set a
temporary BC as exec one. I see no other way that keeps pair
set_exec_bc()/get_exec_bc() lock-less.

The problem is even larger than I've described. set_exec_bc()
is used widely in OpenVZ beancounters to set temporary context
e.g. for skb handling. Thus we need some safe way to "catch"
the task in a "safe" place. In OpenVZ we solve this by moving
only current into beancounter. In this patch set we have to
move arbitrary task and thus - such complication.

I repeat - we can do this w/o stop_machine, but this would
require locking in set_exec_bc()/get_exec_bc() but it's too
bad. Moving tasks happens rarely but setting context is a
very common operation (e.g. in each interrupt).

We can do the following:

if (tsk == current)
/* fast way */
tsk->exec_bc = bc;
else
/* slow way */
stop_machine_run(...);

What do you think?

> Paul
> -
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[Message index]

		BC: resource beancounters (v6) (with userpages reclamation + configfs) By: dev on Thu, 09 November 2006 16:42
		[PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper By: dev on Thu, 09 November 2006 16:47
		Re: [PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper By: Cedric Le Goater on Fri, 10 November 2006 15:19
		Re: [PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper By: dev on Fri, 10 November 2006 16:40
		[PATCH 2/13] BC: Kconfig and Makefile By: dev on Thu, 09 November 2006 16:47
		[PATCH 3/13] BC: beancounters core and API By: dev on Thu, 09 November 2006 16:49
		[PATCH 4/13] BC: context handling By: dev on Thu, 09 November 2006 16:51
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Thu, 23 November 2006 07:48
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Thu, 23 November 2006 08:35
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Thu, 23 November 2006 08:53
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Thu, 23 November 2006 09:20
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Thu, 23 November 2006 09:31
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Thu, 23 November 2006 09:56
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Thu, 23 November 2006 10:18
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Thu, 23 November 2006 10:45
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Fri, 24 November 2006 10:10
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Sat, 25 November 2006 00:09
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Mon, 27 November 2006 08:27
		[PATCH 5/13] BC: configfs interface By: dev on Thu, 09 November 2006 16:52
		[PATCH 6/13] BC: kmemsize accounting (core) By: dev on Thu, 09 November 2006 16:53
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Paul Jackson on Thu, 09 November 2006 19:05
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Pekka Enberg on Fri, 10 November 2006 22:50
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Pekka Enberg on Fri, 10 November 2006 22:46
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Pavel Emelianov on Mon, 13 November 2006 12:13
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Pavel Machek on Sat, 11 November 2006 05:50
		[PATCH 7/13] BC: kmemsize accounting (hooks) By: dev on Thu, 09 November 2006 16:54
		[PATCH 8/13] BC: privvmpages accounting (core) By: dev on Thu, 09 November 2006 16:56
		[PATCH 9/13] BC: privvmpages accounting (hooks) By: dev on Thu, 09 November 2006 16:57
		[PATCH 10/13] BC: physpages accounting (core) By: dev on Thu, 09 November 2006 16:59
		[PATCH 11/13] BC: physpages accounting (hooks) By: dev on Thu, 09 November 2006 17:01
		[PATCH 12/13] BC: numtasks accounting By: dev on Thu, 09 November 2006 17:02
		[PATCH 13/13] BC: numfiles accounting By: dev on Thu, 09 November 2006 17:03
		Re: BC: resource beancounters (v6) (with userpages reclamation + configfs) By: Herbert Poetzl on Sun, 19 November 2006 19:41

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