From: Feng Tang <feng.tang@xxxxxxxxx> Subject: 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. Link: http://lkml.kernel.org/r/1592725000-73486-3-git-send-email-feng.tang@xxxxxxxxx Link: http://lkml.kernel.org/r/1594389708-60781-3-git-send-email-feng.tang@xxxxxxxxx Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> # for /proc/meminfo Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Qian Cai <cai@xxxxxx> Cc: Andi Kleen <andi.kleen@xxxxxxxxx> Cc: Tim Chen <tim.c.chen@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Cc: Huang Ying <ying.huang@xxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Dennis Zhou <dennis@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: kernel test robot <rong.a.chen@xxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/util.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/mm/util.c~mm-utilc-make-vm_memory_committed-more-accurate +++ a/mm/util.c @@ -787,10 +787,15 @@ struct percpu_counter vm_committed_as __ * 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); _
