Alan Burlison created HDFS-9957:
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Summary: HDFS's use of mlock() is not portable
Key: HDFS-9957
URL: https://issues.apache.org/jira/browse/HDFS-9957
Project: Hadoop HDFS
Issue Type: Sub-task
Components: native
Affects Versions: 2.7.2
Environment: Any UNIX system other than Linux
Reporter: Alan Burlison
HDFS uses mlock() to lock in the memory used to back java.nio.Buffer.
Unfortunately the way it is done is not standards-compliant. As the Linux
manpage for mlock() says:
{quote}
Under Linux, mlock(), mlock2(), and munlock() automatically round
addr down to the nearest page boundary. However, the POSIX.1
specification of mlock() and munlock() allows an implementation to
require that addr is page aligned, so portable applications should
ensure this.
{quote}
The HDFS code does not do any such alignment, nor is it true that the backing
buffers for java.nio.Buffer are necessarily page aligned. And even if the
address was aligned by the code, it would end up calling mlock() on other
random JVM data structures that shared the same page. That seems potentially
dangerous.
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