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SubjectRe: [PATCH] thp: reduce khugepaged freezing latency
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


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