Re: OProfile support in Linux 2.5 kernel and do_exit()

[William C. <wc...@nc...>]

I looked throught the code for do_exit() and what it calls related to 
the profiling. It turns out that __exit_mm() ends up calling 
profile_exit_mmap() in do_exit(). Wouldn't that make the 
profile_exit_task() redundant? Below is a diagram of the call chains to 
get from do_exit() to the profile_exit_task() and profile_exit_mmap() 
functions. Each indentation is a call.

do_exit()
	...
	profile_exit_task(tsk);
	...
	__exit_mm(tsk);
		mmput(mm);
			exit_mmap();
				profile_exit_mmap()

There is still a fair amount of code that happens after the __exit_mm(). 
Could the __exit_mm() be moved later in the do_exit()?

-Will


William Cohen wrote:
> John Levon wrote:
> 
>> On Mon, Nov 18, 2002 at 05:29:27PM -0500, William Cohen wrote:
>>
>>
>>> The general premise is if any memory mapping information appears to 
>>> be going away flush the per cpu sample buffer and convert the data 
>>> into a more permanent form. This occurs when there the process exits, 
>>> mmap operation, or unmap operation. The exit verion is handled by 
>>> exit_task_notify(). Both mm operations are handled by mm_notify(). Both 
>>
>>
>>
>> No, the exit is different. It is required (the other flushes are merely
>> for more accurate profiles, and not strictly needed as such). The
>> buffers contain task_struct *, and we must ensure that at
>> free(task_struct)  time there are exactly 0 references to that struct in
>> any of the buffers.
>>
>> regards
>> john
>>
> 
> Yes, OProfile needs to make sure there are absolutely no reference to 
> the task_struct * that has been removed. When exactly does the 
> task_struct * go away? Before or after exit_mmap()? If the task_struct * 
> goes away after mm/mm.c:exit_mmap(), then wouldn't the mm_notify() be 
> sufficient and exit_task_notify() be unneeded?
> 
> -Will
> 
> 
> 
> 
> 
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