Re: Interactivity regression since v3.11 in mm/vmscan.c

[Felipe Contreras]

On Thu, Jun 5, 2014 at 8:37 AM, Michal Hocko <mhocko@xxxxxxx> wrote:
> On Thu 05-06-14 06:33:40, Felipe Contreras wrote:

>> For a while I've noticed that my machine bogs down in certain
>> situations, usually while doing heavy I/O operations, it is not just the
>> I/O operations, but everything, including the graphical interface, even
>> the mouse pointer.
>>
>> As far as I can recall this did not happen in the past.
>>
>> I noticed this specially on certain operations, for example updating a
>> a game on Steam (to an exteranl USB 3.0 device), or copying TV episodes
>> to a USB memory stick (probably flash-based).
>
> We had a similar report for opensuse. The common part was that there was
> an IO to a slow USB device going on.

Well, it's a USB 3.0 device, I can write at 250 MB/s, so it's not
really that slow.

And in fact, when I read and write to and from the same USB 3.0
device, I don't see the issue.

>> Then I went back to the latest stable version (v3.14.5), and commented
>> out the line I think is causing the slow down:
>>
>>   if (nr_unqueued_dirty == nr_taken || nr_immediate)
>>         congestion_wait(BLK_RW_ASYNC, HZ/10);
>
> Yes, I came to the same check. I didn't have any confirmation yet so
> thanks for your confirmation. I've suggested to reduce this
> congestion_wait only to kswapd:
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 32c661d66a45..ef6a1c0e788c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1566,7 +1566,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>                  * implies that pages are cycling through the LRU faster than
>                  * they are written so also forcibly stall.
>                  */
> -               if (nr_unqueued_dirty == nr_taken || nr_immediate)
> +               if ((nr_unqueued_dirty == nr_taken || nr_immediate) && current_is_kswapd())
>                         congestion_wait(BLK_RW_ASYNC, HZ/10);
>         }

Unfortunately that doesn't fix the issue for me.

-- 
Felipe Contreras
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