Re: [PATCH] thp: reduce khugepaged freezing latency

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

On 11/09/2011 09:23 PM, Tejun Heo wrote:
> Hello, Andrea, Srivatsa.
> 
> On Wed, Nov 09, 2011 at 06:15:38PM +0530, Srivatsa S. Bhat wrote:
>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>>> index 4298aba..67311d1 100644
>>>> --- a/mm/huge_memory.c
>>>> +++ b/mm/huge_memory.c
>>>> @@ -2277,6 +2277,7 @@ static struct page *khugepaged_alloc_hugepage(void)
>>>>  		if (!hpage) {
>>>>  			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
>>>>  			khugepaged_alloc_sleep();
>>>> +			try_to_freeze();
>>>>  		} else
>>>>  			count_vm_event(THP_COLLAPSE_ALLOC);
>>>>  	} while (unlikely(!hpage) &&
>>>> @@ -2331,7 +2332,7 @@ static int khugepaged(void *none)
>>>>  {
>>>>  	struct mm_slot *mm_slot;
>>>>
>>>> -	set_freezable();
>>>> +	set_freezable_with_signal();
>>>>  	set_user_nice(current, 19);
> 
> Oooh, please don't do that.  It's already gone in the pm tree.  It
> would be best if wait_event_freezable_timeout() can be used
> (ie. wakeup condition should be set somewhere) but, if not, something
> like the following sould work.
> 
> static void khugepaged_alloc_sleep(void)
> {
> 	DEFINE_WAIT(wait);
> 	add_wait_queue(&khugepaged_wait, &wait);
> 	try_to_freeze();
> 	schedule_timeout_interruptible(
> 			msecs_to_jiffies(
> 				khugepaged_alloc_sleep_millisecs));
> 	try_to_freeze();
> 	remove_wait_queue(&khugepaged_wait, &wait);
> }
> 												

Right, Andrea this is what I meant. First of all we don't need both
set_freezable_with_signal() _and_ an additional try_to_freeze().
And since we are anyway doing away with set_freezable_with_signal(),
we can just use try_to_freeze() as Tejun suggested above.  

Thanks,
Srivatsa S. Bhat