> > ============================================================= > > Subject: [PATCH] Call cond_resched() at bottom of main look in balance_pgdat() > > From: Larry Woodman <lwoodman@xxxxxxxxxx> > > > > We are seeing a problem where kswapd gets stuck and hogs the CPU on a > > small single CPU system when an OOM kill should occur. When this > > happens swap space has been exhausted and the pagecache has been shrunk > > to zero. Once kswapd gets the CPU it never gives it up because at least > > one zone is below high. Adding a single cond_resched() at the end of > > the main loop in balance_pgdat() fixes the problem by allowing the > > watchdog and tasks to run and eventually do an OOM kill which frees up > > the resources. > > > > kosaki note: This seems regression caused by commit bb3ab59683 > > (vmscan: stop kswapd waiting on congestion when the min watermark is > > not being met) > > > > Signed-off-by: Larry Woodman <lwoodman@xxxxxxxxxx> > > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > --- > > mm/vmscan.c | 1 + > > 1 files changed, 1 insertions(+), 0 deletions(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 9c7e57c..c5c46b7 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -2182,6 +2182,7 @@ loop_again: > > */ > > if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) > > break; > > + cond_resched(); > > } > > out: > > /* > > -- > > 1.6.5.2 > > Kosaki's patch's goal is that kswap doesn't yield cpu if the zone doesn't meet its > min watermark to avoid failing atomic allocation. > But this patch could yield kswapd's time slice at any time. > Doesn't the patch break your goal in bb3ab59683? No. it don't break. Typically, kswapd periodically call shrink_page_list() and it call cond_resched() even if bb3ab59683 case. Larry observed very exceptional situation. his system don't have reclaimable pages at all, then eventually shrink_page_list() was not called very long time. His patch only change such very rare situation, I think it's safe. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>