alluxio worker OOMKilled

[XiXiTan]

Alluxio Version:
What version of Alluxio are you using?
2.9.0.1

Describe the bug
A clear and concise description of what the bug is.
内存设置有富裕，但worker pod会出现被OOMKilled情况。
请教可能是哪块儿内存使用超出预期？以及缓存为啥会用超过设置的取值？

pod申请资源： cpu: 4 memory: 16G
使用资源： xmx=4g MaxDirectMemorySize=4g alluxio.worker.ramdisk.size=6g 预留内存=2g

具体内存设置：
/usr/lib/jvm/java-1.8.0-openjdk/bin/java -cp /opt/alluxio-2.9.0.1-noHelm/conf/::/opt/alluxio/ranger-lib/*:/opt/alluxio-2.9.0.1-noHelm/assembly/alluxio-server-2.9.0.1.jar -Dalluxio.logger.type=Console,WORKER_LOGGER -Dsun.security.krb5.disableReferrals=true -Dalluxio.home=/opt/alluxio-2.9.0.1-noHelm -Dalluxio.conf.dir=/opt/alluxio-2.9.0.1-noHelm/conf -Dalluxio.logs.dir=/opt/alluxio-2.9.0.1-noHelm/logs -Dalluxio.user.logs.dir=/opt/alluxio-2.9.0.1-noHelm/logs/user -Dlog4j.configuration=file:/opt/alluxio-2.9.0.1-noHelm/conf/log4j.properties -Dorg.apache.jasper.compiler.disablejsr199=true -Djava.net.preferIPv4Stack=true -Dorg.apache.ratis.thirdparty.io.netty.allocator.useCacheForAllThreads=false -Dalluxio.worker.hostname=ip -Xmx4096M -XX:MaxDirectMemorySize=4096M alluxio.worker.AlluxioWorker

conf/alluxio-site.properties
alluxio.worker.ramdisk.size=6144M

缓存使用：

出问题pod的cpu、mem情况

To Reproduce
Steps to reproduce the behavior (as minimally and precisely as possible)

Expected behavior
A clear and concise description of what you expected to happen.
worker pod不要OOMKilled

Urgency
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Are you planning to fix it
Please indicate if you are already working on a PR.

Additional context
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[XiXiTan]

另一个小问题：
如果worker缓存设置为512M，实际会使用1024M。这超过了缓存设置512，和woker缓存使用预期不符。
MEM HDD
capacity 30.50GB 512.00MB 30.00GB
used 4083.94MB (13%) 1024.00MB 3059.94MB

源码中只看到对于未设定缓存时的默认值，会取系统获取2/3内存或者给1g。没有看到对于指定缓存时，会取其他值的逻辑。

`

public static final PropertyKey WORKER_RAMDISK_SIZE =
dataSizeBuilder(Name.WORKER_RAMDISK_SIZE)
.setAlias(Name.WORKER_MEMORY_SIZE)
.setDefaultSupplier(() -> {
try {
OperatingSystemMXBean operatingSystemMXBean =
(OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
return operatingSystemMXBean.getTotalPhysicalMemorySize() * 2 / 3;
} catch (Throwable e) {
// The package com.sun.management may not be available on every platform.
// fallback to a reasonable size.
return "1GB";
}
}, "2/3 of total system memory, or 1GB if system memory size cannot be determined")
.setDescription("The allocated memory for each worker node's ramdisk(s). "
+ "It is recommended to set this value explicitly.")
.setConsistencyCheckLevel(ConsistencyCheckLevel.WARN)
.setScope(Scope.WORKER)
.build();

`