lrud kernel thread

The AIX Least Recently Used Daemon, invoked when memory is required, is responsible for scanning cached file pages (the buffer cache) in memory and freeing those not recently accessed. On an MP kernel in 4.3.3 and later, it is multi-threaded with the cached file pages broken up into multiple lists, whose size is controlled by the lrubucket parameter. Consistently high CPU usage by lrud indicates large amounts of file I/O occurring, and thrashing of the VMM file cache.

If high paging rates are also seen, especially paging to and from swap spaces, identified by the pi and po columns in vmstat or the pgspin and pgspout entries in topas, then Tuning the AIX file caches should be a priority.

If lrud is consistently using high CPU on a system running a database engine that employs its own caching (e.g. Oracle, DB2, TSM, PostgreSQL), then the use of raw logical volumes or AIX direct I/O may considerably improve performance.

See Tuning the AIX file caches for a description of some of the AIX parameters that directly impact the way that lrud operates.

See Also

Internal

• direct I/O
• concurrent I/O
• Tuning the AIX file caches

External

• Oracle 9i & 10g on IBM AIX5L: Tips & Considerations White Paper. Document ID WP100556.
• JFS2/DIO Sequential Input/Output Performance on IBM pSeries 690 Redpaper. IBM Form Number REDP-9122-00.