hi all
On Wed, Apr 30, 2014 at 11:42 PM, Kirill A. Shutemov
<kirill@xxxxxxxxxxxxx> wrote:
> On Tue, Apr 15, 2014 at 10:06:56PM -0400, Sasha Levin wrote:
>> Hi all,
>>
>> I often see hung task triggering in khugepaged within collapse_huge_page().
>>
>> I've initially assumed the case may be that the guests are too loaded and
>> the warning occurs because of load, but after increasing the timeout to
>> 1200 sec I still see the warning.
>
> I suspect it's race (although I didn't track down exact scenario) with
> __khugepaged_exit().
>
> Comment in __khugepaged_exit() says that khugepaged_test_exit() always
> called under mmap_sem:
>
> 2045 void __khugepaged_exit(struct mm_struct *mm)
> ...
> 2063 } else if (mm_slot) {
> 2064 /*
> 2065 * This is required to serialize against
> 2066 * khugepaged_test_exit() (which is guaranteed to run
> 2067 * under mmap sem read mode). Stop here (after we
> 2068 * return all pagetables will be destroyed) until
> 2069 * khugepaged has finished working on the pagetables
> 2070 * under the mmap_sem.
> 2071 */
> 2072 down_write(&mm->mmap_sem);
> 2073 up_write(&mm->mmap_sem);
> 2074 }
> 2075 }
>
> But this is not true. At least khugepaged_scan_mm_slot() calls it without
> the sem:
>
> 2566 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
> 2567 struct page **hpage)
> ...
> 2046 {
> 2047 struct mm_slot *mm_slot;
> 2048 int free = 0;
> 2049
> 2050 spin_lock(&khugepaged_mm_lock);
> 2051 mm_slot = get_mm_slot(mm);
> 2052 if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
> 2053 hash_del(&mm_slot->hash);
> 2054 list_del(&mm_slot->mm_node);
> 2055 free = 1;
> 2056 }
> 2057 spin_unlock(&khugepaged_mm_lock);
> 2058
> 2059 if (free) {
> 2060 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
> 2061 free_mm_slot(mm_slot);
> 2062 mmdrop(mm);
>
> Not sure yet if it's a real problem or not. Andrea, could you comment on
> this?
>
> Sasha, please try patch below.
>
This box is quite,
CPU: 0 PID: 0 Comm: swapper/0
CPU: 1 PID: 0 Comm: swapper/1
CPU: 2 PID: 0 Comm: swapper/2
CPU: 3 PID: 0 Comm: swapper/3
CPU: 4 PID: 0 Comm: swapper/4
CPU: 5 PID: 0 Comm: swapper/5
CPU: 6 PID: 0 Comm: swapper/6
CPU: 7 PID: 0 Comm: swapper/7
CPU: 8 PID: 0 Comm: swapper/8
CPU: 9 PID: 0 Comm: swapper/9
CPU: 10 PID: 0 Comm: swapper/10
CPU: 11 PID: 0 Comm: swapper/11
CPU: 12 PID: 0 Comm: swapper/12
CPU: 13 PID: 0 Comm: swapper/13
CPU: 14 PID: 0 Comm: swapper/14
CPU: 15 PID: 0 Comm: swapper/15
CPU: 16 PID: 0 Comm: swapper/16
CPU: 17 PID: 0 Comm: swapper/17
CPU: 18 PID: 0 Comm: swapper/18
CPU: 19 PID: 0 Comm: swapper/19
CPU: 20 PID: 0 Comm: swapper/20
CPU: 21 PID: 3540 Comm: khungtaskd
CPU: 22 PID: 0 Comm: swapper/22
CPU: 23 PID: 0 Comm: swapper/23
and lets make more noise.
Hillf
---
--- a/mm/huge_memory.c Thu May 1 22:20:20 2014
+++ b/mm/huge_memory.c Thu May 1 22:24:06 2014
@@ -2732,7 +2732,8 @@ static void khugepaged_wait_work(void)
}
if (khugepaged_enabled())
- wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
+ wait_event_freezable_timeout(khugepaged_wait, khugepaged_wait_event(),
+ msecs_to_jiffies(2000));
}
static int khugepaged(void *none)
--
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>