sysbench Cannot allocate memory

sysbench --test=threads --num-threads=1500 run
sysbench v0.4.8:  multi-threaded system evaluation benchmark

Running the test with following options:
Number of threads: 1500

Doing thread subsystem performance test
Thread yields per test: 1000 Locks used: 8
FATAL: Thread #305 creation failed errno = 12 (Cannot allocate memory)

ulimit -a
core file size        (blocks, -c) 0
data seg size         (kbytes, -d) unlimited
file size             (blocks, -f) unlimited
max locked memory     (kbytes, -l) 4
max memory size       (kbytes, -m) unlimited
open files                    (-n) 1024
pipe size          (512 bytes, -p) 8
stack size            (kbytes, -s) 10240
cpu time             (seconds, -t) unlimited
max user processes            (-u) 7168
virtual memory        (kbytes, -v) unlimited

ulimit -s 1024

sysbench --test=threads --num-threads=1500 run
sysbench v0.4.8:  multi-threaded system evaluation benchmark

Running the test with following options:
Number of threads: 1500

Doing thread subsystem performance test
Thread yields per test: 1000 Locks used: 8
Threads started!

用ulimit -s把stack size改小，就可以创建更多的线程而不导致内存不够。