Re: [v5][PATCH 6/6] mm: vmscan: drain batch list during long operations

Minchan Kim
2013-06-04T23:23:22Z

Hello Dave,

On Tue, Jun 04, 2013 at 08:24:38AM -0700, Dave Hansen wrote:
> On 06/03/2013 11:05 PM, Minchan Kim wrote:
> >> > This ensures that we drain the batch if we are about to perform a
> >> > pageout() or congestion_wait(), either of which will take some
> >> > time. We expect this to help mitigate the worst of the latency
> >> > increase that the batching could cause.
> > Nice idea but I could see drain before pageout but congestion_wait?
>
> That comment managed to bitrot a bit :(
>
> The first version of these had the drain before pageout() only. Then,
> Mel added a congestion_wait() call, and I modified the series to also
> drain there. But, some other patches took the congestion_wait() back
> out, so I took that drain back out.

I am looking next-20130530 and it has still a congestion_wait.
I'm confusing. :(

if (PageWriteback(page)) {
/* Case 1 above */
if (current_is_kswapd() &&
PageReclaim(page) &&
zone_is_reclaim_writeback(zone)) {
congestion_wait(BLK_RW_ASYNC, HZ/10);
zone_clear_flag(zone, ZONE_WRITEBACK);
>
> I _believe_ the only congestion_wait() left in there is a cgroup-related
> one that we didn't think would cause very much harm.

The congestion_wait I am seeing is not cgroup-related one.

I'd like to clear this confusing.
Thanks.

>
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--
Kind regards,
Minchan Kim