今天在一台机器上查看java进行时，运行jps -m时报如下错误：
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Error occurred during initialization of VM
Could not reserve enough space
for
object heap
Could not create the Java virtual machine.
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但其实服务器的内存是充足的：
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free
-m
total used
free
shared buffers cached
Mem: 64412 27418 36994 0 174 13226
-/+ buffers
/cache
: 14018 50394
Swap: 0 0 0
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这其实是由于一个系统的参数导致：
vm.overcommit_memory
这个可以用来控制对应用分配内存的限制，默认是0，关于这个参数
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0 — The default setting. The kernel performs heuristic memory overcommit
handling by estimating the amount of memory available and failing requests
that are blatantly invalid. Unfortunately, since memory is allocated using
a heuristic rather than a precise algorithm, this setting can sometimes allow
available memory on the system to be overloaded.
1 — The kernel performs no memory overcommit handling. Under this setting,
the potential
for
memory overload is increased, but so is performance
for
memory-intensive tasks.
2 — The kernel denies requests
for
memory equal to or larger than the
sum
of
total available swap and the percentage of physical RAM specified
in
overcommit_ratio.
This setting is best
if
you want a lesser risk of memory overcommitment.
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可以看出2是比较严格的限制，1是最宽松的限制，对于不同的应用对这个参数的要求页不一样。
比如对于greenplum来说，是不允许使用swap的，所以参数要设置为2.
而对于redis应用，因为在bgsave的时候，需要2倍的使用内存，所以建议设置为1.
java的应用设置为0或1都是可以的。
本文转自菜菜光 51CTO博客，原文链接：http://blog.51cto.com/caiguangguang/1395596，如需转载请自行联系原作者
