path: root/kernel
diff options
authorHugh Dickins <>2016-05-19 17:12:50 -0700
committerLinus Torvalds <>2016-05-19 19:12:14 -0700
commit52b6f46bc163eef17ecba4cd552beeafe2b24453 (patch)
treef1f8a9dc258f548fcdb7fa63b9b9a5eebd17976f /kernel
parent9e18eb29356b7dfd55183bd42cf73919d1590835 (diff)
mm: /proc/sys/vm/stat_refresh to force vmstat update
Provide /proc/sys/vm/stat_refresh to force an immediate update of per-cpu into global vmstats: useful to avoid a sleep(2) or whatever before checking counts when testing. Originally added to work around a bug which left counts stranded indefinitely on a cpu going idle (an inaccuracy magnified when small below-batch numbers represent "huge" amounts of memory), but I believe that bug is now fixed: nonetheless, this is still a useful knob. Its schedule_on_each_cpu() is probably too expensive just to fold into reading /proc/meminfo itself: give this mode 0600 to prevent abuse. Allow a write or a read to do the same: nothing to read, but "grep -h Shmem /proc/sys/vm/stat_refresh /proc/meminfo" is convenient. Oh, and since global_page_state() itself is careful to disguise any underflow as 0, hack in an "Invalid argument" and pr_warn() if a counter is negative after the refresh - this helped to fix a misaccounting of NR_ISOLATED_FILE in my migration code. But on recent kernels, I find that NR_ALLOC_BATCH and NR_PAGES_SCANNED often go negative some of the time. I have not yet worked out why, but have no evidence that it's actually harmful. Punt for the moment by just ignoring the anomaly on those. Signed-off-by: Hugh Dickins <> Cc: "Kirill A. Shutemov" <> Cc: Andrea Arcangeli <> Cc: Andres Lagar-Cavilla <> Cc: Yang Shi <> Cc: Ning Qu <> Cc: Mel Gorman <> Cc: Andres Lagar-Cavilla <> Cc: Konstantin Khlebnikov <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'kernel')
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c8b318663525..2effd84d83e3 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1521,6 +1521,13 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec_jiffies,
+ {
+ .procname = "stat_refresh",
+ .data = NULL,
+ .maxlen = 0,
+ .mode = 0600,
+ .proc_handler = vmstat_refresh,
+ },