kswapd: assign new_order and new_classzone_idx after wakeup in sleeping
commit f0dfcde099453aa4c0dc42473828d15a6d492936 upstream.
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 <firstname.lastname@example.org>
Acked-by: Mel Gorman <email@example.com>
Reviewed-by: Minchan Kim <firstname.lastname@example.org>
Tested-by: Pádraig Brady <P@draigBrady.com>
Signed-off-by: Andrew Morton <email@example.com>
Signed-off-by: Linus Torvalds <firstname.lastname@example.org>
Signed-off-by: Mel Gorman <email@example.com>
Signed-off-by: Greg Kroah-Hartman <firstname.lastname@example.org>
1 file changed