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 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 <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Acked-by: Michal Hocko <[email protected]> # for /proc/meminfo
Cc: "K. Y. Srinivasan" <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Qian Cai <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Dennis Zhou <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: kernel test robot <[email protected]>
Cc: Tejun Heo <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions