On 2017年12月19日 20:40, Michal Hocko wrote:
> On Tue 19-12-17 14:39:24, Kemi Wang wrote:
>> We have seen significant overhead in cache bouncing caused by NUMA counters
>> update in multi-threaded page allocation. See 'commit 1d90ca897cb0 ("mm:
>> update NUMA counter threshold size")' for more details.
>>
>> This patch updates NUMA counters to a fixed size of (MAX_S16 - 2) and deals
>> with global counter update using different threshold size for node page
>> stats.
>
> Again, no numbers.
Compare to vanilla kernel, I don't think it has performance improvement, so
I didn't post performance data here.
But, if you would like to see performance gain from enlarging threshold size
for NUMA stats (compare to the first patch), I will do that later.
> To be honest I do not really like the special casing
> here. Why are numa counters any different from PGALLOC which is
> incremented for _every_ single page allocation?
>
I guess you meant to PGALLOC event.
The number of this event is kept in local cpu and sum up (for_each_online_cpu)
when need. It uses the similar way to what I used before for NUMA stats in V1
patch series. Good enough.
>> ---
>> mm/vmstat.c | 13 +++++++++++--
>> 1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>> index 9c681cc..64e08ae 100644
>> --- a/mm/vmstat.c
>> +++ b/mm/vmstat.c
>> @@ -30,6 +30,8 @@
>>
>> #include "internal.h"
>>
>> +#define VM_NUMA_STAT_THRESHOLD (S16_MAX - 2)
>> +
>> #ifdef CONFIG_NUMA
>> int sysctl_vm_numa_stat = ENABLE_NUMA_STAT;
>>
>> @@ -394,7 +396,11 @@ void __inc_node_state(struct pglist_data *pgdat, enum
>> node_stat_item item)
>> s16 v, t;
>>
>> v = __this_cpu_inc_return(*p);
>> - t = __this_cpu_read(pcp->stat_threshold);
>> + if (item >= NR_VM_NUMA_STAT_ITEMS)
>> + t = __this_cpu_read(pcp->stat_threshold);
>> + else
>> + t = VM_NUMA_STAT_THRESHOLD;
>> +
>> if (unlikely(v > t)) {
>> s16 overstep = t >> 1;
>>
>> @@ -549,7 +555,10 @@ static inline void mod_node_state(struct pglist_data
>> *pgdat,
>> * Most of the time the thresholds are the same anyways
>> * for all cpus in a node.
>> */
>> - t = this_cpu_read(pcp->stat_threshold);
>> + if (item >= NR_VM_NUMA_STAT_ITEMS)
>> + t = this_cpu_read(pcp->stat_threshold);
>> + else
>> + t = VM_NUMA_STAT_THRESHOLD;
>>
>> o = this_cpu_read(*p);
>> n = delta + o;
>> --
>> 2.7.4
>>
>
