Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 27/40] kswapd: assign new order and new classzone idx after wakeup in sleeping | Date | Thu, 26 Jul 2012 14:29:45 -0700 |
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From: Greg KH <gregkh@linuxfoundation.org>
3.0-stable review patch. If anyone has any objections, please let me know.
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From: Alex Shi <alex.shi@intel.com>
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 <alex.shi@intel.com> Acked-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Tested-by: Pádraig Brady <P@draigBrady.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/vmscan.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2908,6 +2908,8 @@ 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; }
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