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Date:   Sat, 16 May 2020 14:47:39 +0800
From:   Feng Tang <>
To:     Andrew Morton <>,
        Michal Hocko <>,
        Matthew Wilcox <>,
        Johannes Weiner <>,
        Mel Gorman <>,
        Kees Cook <>,,,,,,
Cc:     Feng Tang <>
Subject: [PATCH v3 2/3] mm/util.c: make vm_memory_committed() more accurate

percpu_counter_sum_positive() will provide more accurate info.

As with percpu_counter_read_positive(), in worst case the deviation
could be 'batch * nr_cpus', which is totalram_pages/256 for now,
and will be more when the batch gets enlarged.

Its time cost is about 800 nanoseconds on a 2C/4T platform and
2~3 microseconds on a 2S/36C/72T server in normal case, and in
worst case where vm_committed_as's spinlock is under severe
contention, it costs 30~40 microseconds for the 2S/36C/72T sever,
which should be fine for its only two users: /proc/meminfo and
HyperV balloon driver's status trace per second.

Signed-off-by: Feng Tang <>
 mm/util.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/util.c b/mm/util.c
index 988d11e..3de78e9 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -774,7 +774,7 @@ struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp;
 unsigned long vm_memory_committed(void)
-	return percpu_counter_read_positive(&vm_committed_as);
+	return percpu_counter_sum_positive(&vm_committed_as);

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