Messages in this thread Patch in this message | | | Date | Thu, 20 Aug 2009 10:52:09 +0800 | From | Wu Fengguang <> | Subject | [PATCH] mm: make nr_scan_try_batch() more safe on races |
| |
nr_scan_try_batch() can be called concurrently on the same zone and the non-atomic calculations can go wrong. This is not a big problem as long as the errors are small and won't impact the balanced zone aging noticeably.
@nr_to_scan could be much larger values than @swap_cluster_max. So don't store such large values to *nr_saved_scan directly, which helps reducing possible errors on races.
CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> --- mm/vmscan.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
--- linux.orig/mm/vmscan.c 2009-08-20 10:46:30.000000000 +0800 +++ linux/mm/vmscan.c 2009-08-20 10:49:36.000000000 +0800 @@ -1496,15 +1496,14 @@ static unsigned long nr_scan_try_batch(u unsigned long *nr_saved_scan, unsigned long swap_cluster_max) { - unsigned long nr; - - *nr_saved_scan += nr_to_scan; - nr = *nr_saved_scan; + unsigned long nr = *nr_saved_scan + nr_to_scan; if (nr >= swap_cluster_max) *nr_saved_scan = 0; - else + else { + *nr_saved_scan = nr; nr = 0; + } return nr; }
| |