https://bugzilla.novell.com/show_bug.cgi?id=879071
https://bugzilla.novell.com/show_bug.cgi?id=879071#c9
--- Comment #9 from Michal Hocko 2014-05-27 14:05:54 CEST ---
Just for reference. The congestion wait was called here:
/*
* In addition, if kswapd scans pages marked marked for
* immediate reclaim and under writeback (nr_immediate), it
* 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))
congestion_wait(BLK_RW_ASYNC, HZ/10);
which tells us that all pages which have been isolated from LRUs by the direct
reclaimer are dirty and not under writeback. So the writeback is clearly not
fast enough.
I am wondering whether this stall is really appropriate for the direct reclaim
because it can get throttled again right after in wait_iff_congested. Would it
make sense to reduce the above congestion_wait only for kswapd?
Anyway even with something like that in place we could still wait on the
iff_congested so I am not sure how much helpful this would be. If we had more
direct reclaimers and one would manage to free some pages then throttling
another one doesn't sound seem necessary...
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