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 Skylake 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 Skylake
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 <feng.t...@intel.com>
Acked-by: Michal Hocko <mho...@suse.com> # for /proc/meminfo
Cc: "K. Y. Srinivasan" <k...@microsoft.com>
Cc: Haiyang Zhang <haiya...@microsoft.com>
Cc: Matthew Wilcox (Oracle) <wi...@infradead.org>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Mel Gorman <mgor...@suse.de>
Cc: Andi Kleen <andi.kl...@intel.com>
Cc: Tim Chen <tim.c.c...@intel.com>
Cc: Dave Hansen <dave.han...@intel.com>
Cc: Huang Ying <ying.hu...@intel.com>
---
mm/util.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/util.c b/mm/util.c
index c63c8e4..1c9d097 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -787,10 +787,15 @@ struct percpu_counter vm_committed_as
____cacheline_aligned_in_smp;
* balancing memory across competing virtual machines that are hosted.
* Several metrics drive this policy engine including the guest reported
* memory commitment.
+ *
+ * The time cost of this is very low for small platforms, and for big
+ * platform like a 2S/36C/72T Skylake server, in worst case where
+ * vm_committed_as's spinlock is under severe contention, the time cost
+ * could be about 30~40 microseconds.
*/
unsigned long vm_memory_committed(void)
{
- return percpu_counter_read_positive(&vm_committed_as);
+ return percpu_counter_sum_positive(&vm_committed_as);
}
EXPORT_SYMBOL_GPL(vm_memory_committed);
--
2.7.4
