[HDFS-9957] HDFS's use of mlock() is not portable

• Type: Sub-task
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.7.2
• Component/s: native

Environment

Any UNIX system other than Linux

• Assignee: Alan Burlison
• Reporter: Alan Burlison
• Created: 14/Mar/16 17:03
• Updated: 22/Sep/17 16:16

Description

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:

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.

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.

Issue Links

• relates to: HDFS-4949 Centralized cache management in HDFS