On Thu, 19 Jul 2012, Mel Gorman wrote: > From: "Alex,Shi" <alex.shi@xxxxxxxxx> > > commit d2ebd0f6b89567eb93ead4e2ca0cbe03021f344b upstream. Thanks for assembling these, Mel: I was checking through to see if I was missing any, and noticed that this one has the wrong upstream SHA1: the one you give here is the same as in 20/34, but it should be commit f0dfcde099453aa4c0dc42473828d15a6d492936 upstream. I got quite confused by 30/34 too: interesting definition of "partial backport" :) I've no objection, but "substitute" might be clearer there. Hugh > > Stable note: Fixes https://bugzilla.redhat.com/show_bug.cgi?id=712019. This > patch reduces kswapd CPU usage. > > There 2 places to read pgdat in kswapd. One is return from a successful > balance, another is waked up from kswapd sleeping. The new_order and > new_classzone_idx represent the balance input order and classzone_idx. > > But current new_order and new_classzone_idx are not assigned after > kswapd_try_to_sleep(), that will cause a bug in the following scenario. > > 1: after a successful balance, kswapd goes to sleep, and new_order = 0; > new_classzone_idx = __MAX_NR_ZONES - 1; > > 2: kswapd waked up with order = 3 and classzone_idx = ZONE_NORMAL > > 3: in the balance_pgdat() running, a new balance wakeup happened with > order = 5, and classzone_idx = ZONE_NORMAL > > 4: the first wakeup(order = 3) finished successufly, return order = 3 > but, the new_order is still 0, so, this balancing will be treated as a > failed balance. And then the second tighter balancing will be missed. > > So, to avoid the above problem, the new_order and new_classzone_idx need > to be assigned for later successful comparison. > > Signed-off-by: Alex Shi <alex.shi@xxxxxxxxx> > Acked-by: Mel Gorman <mgorman@xxxxxxx> > Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> > Tested-by: Pádraig Brady <P@xxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > --- > mm/vmscan.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index bf85e4d..b8c1fc0 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2905,6 +2905,8 @@ static int kswapd(void *p) > balanced_classzone_idx); > order = pgdat->kswapd_max_order; > classzone_idx = pgdat->classzone_idx; > + new_order = order; > + new_classzone_idx = classzone_idx; > pgdat->kswapd_max_order = 0; > pgdat->classzone_idx = pgdat->nr_zones - 1; > } > -- > 1.7.9.2 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> >