hulk inclusion
category: feature
bugzilla: 13228
CVE: NA
---------------------------

hugetlbfs_fallocate preallocates huge pages to back a file in a
hugetlbfs filesystem.  The time to call this function grows linearly
with size.

ktask performs well with its default thread count of 4; higher thread
counts are given for context only.

Machine: Intel(R) Xeon(R) CPU E7-8895 v3 @ 2.60GHz, 288 CPUs, 1T memory
Test:    fallocate(1) a file on a hugetlbfs filesystem

nthread   speedup   size (GiB)   min time (s)   stdev
      1                    200         127.53    2.19
      2     3.09x          200          41.30    2.11
      4     5.72x          200          22.29    0.51
      8     9.45x          200          13.50    2.58
     16     9.74x          200          13.09    1.64

      1                    400         193.09    2.47
      2     2.14x          400          90.31    3.39
      4     3.84x          400          50.32    0.44
      8     5.11x          400          37.75    1.23
     16     6.12x          400          31.54    3.13

The primary bottleneck for better scaling at higher thread counts is
hugetlb_fault_mutex_table[hash].  perf showed L1-dcache-loads increase
with 8 threads and again sharply with 16 threads, and a CPU counter
profile showed that 31% of the L1d misses were on
hugetlb_fault_mutex_table[hash] in the 16-thread case.
Signed-off-by: NDaniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: NHongbo Yao <yaohongbo@huawei.com>
Reviewed-by: NXie XiuQi <xiexiuqi@huawei.com>
Tested-by: NHongbo Yao <yaohongbo@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>