linux-kernel - Re: [Fwd: [-mm] Add an owner to the mm

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Message-ID: <4806C633.3000302@linux.vnet.ibm.com>
Date:	Thu, 17 Apr 2008 09:08:27 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
CC:	Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, serue@...ibm.com,
	penberg@...helsinki.fi, linux-kernel@...r.kernel.org
Subject: Re: [Fwd: [-mm] Add an owner to the mm_struct (v9)]

Oleg Nesterov wrote:
> On 04/15, Paul Menage wrote:
>> On Tue, Apr 15, 2008 at 10:13 AM, Oleg Nesterov <oleg@...sign.ru> wrote:
>>>  Let's suppose the process with a lot of threads does exit_group() and nobody
>>>  else uses this ->mm. How many time we will re-assign mm->owner and iterate
>>>  over the all threads in system ?
>>>
>> In general we won't get to the third loop, since one of the first two
>> loops (children or siblings) will find another mm user.
> 
> Well yes, the second loop checks parent->children ... all sub-threads have
> the same parent.
> 
> I'd suggest to use ->real_parent though. And the third loop could be
> 

real_parent is for ptraced processes right?

> 	for_each_process(g) {
> 		c = g;
> 		do {
> 			if (!c->mm)
> 				continue;
> 			if (c->mm != mm)
> 				break;
> 			goto assign_new_owner;
> 		} while_each_thread(g, c);
> 	}
> 

I had this loop earlier (inspired from zap_threads()), is this loop more
efficient than what we have?

> Still. can't we make mm->mm_users_list ?
> 

I suspect that will be expensive to maintain. Specially with large number of
threads. I see a large space overhead and time overhead and additional
synchronization overhead. Apart from finding the next owner is there any other
advantage?

> Oleg.
> 


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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