On 12 March 2018 at 14:00, Kirill A. Shutemov <kirill@shutemov.name> wrote:
> On Sun, Mar 11, 2018 at 11:11:52PM +0500, Mikhail Gavrilov wrote:
>> $ uname -a
>> Linux localhost.localdomain 4.15.7-300.fc27.x86_64+debug #1 SMP Wed
>> Feb 28 17:32:16 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
>>
>>
>> How reproduce:
>> 1. start virtual machine
>> 2. open https://oom.sy24.ru/ in Firefox which will helps occurred OOM.
>> Sorry I can't attach here html page because my message will rejected
>> as message would contained HTML subpart.
>>
>> Actual result virtual machine hang and even couldn't be force off.
>>
>> Expected result virtual machine continue work.
>>
>> [ 2335.903277] INFO: task CPU 0/KVM:7450 blocked for more than 120 seconds.
>> [ 2335.903284]       Not tainted 4.15.7-300.fc27.x86_64+debug #1
>> [ 2335.903287] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
>> disables this message.
>> [ 2335.903291] CPU 0/KVM       D10648  7450      1 0x00000000
>> [ 2335.903298] Call Trace:
>> [ 2335.903308]  ? __schedule+0x2e9/0xbb0
>> [ 2335.903318]  ? __lock_page+0xad/0x180
>> [ 2335.903322]  schedule+0x2f/0x90
>> [ 2335.903327]  io_schedule+0x12/0x40
>> [ 2335.903331]  __lock_page+0xed/0x180
>> [ 2335.903338]  ? page_cache_tree_insert+0x130/0x130
>> [ 2335.903347]  deferred_split_scan+0x318/0x340
>
> I guess it's bad idea to wait the page to be unlocked in the relaim path.
> Could you check if this makes a difference:
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 87ab9b8f56b5..529cf36b7edb 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2783,11 +2783,13 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>
>         list_for_each_safe(pos, next, &list) {
>                 page = list_entry((void *)pos, struct page, mapping);
> -               lock_page(page);
> +               if (!trylock_page(page))
> +                       goto next;
>                 /* split_huge_page() removes page from list on success */
>                 if (!split_huge_page(page))
>                         split++;
>                 unlock_page(page);
> +next:
>                 put_page(page);
>         }
>

Kiril,thanks for pay attention to the problem.
But your patch couldn't help. Virtual machine was hang after OOM.
New dmesg is attached.



--
Best Regards,
Mike Gavrilov.