It also gives clear statistics about memory usage, CPU Load, system faults and paging activity – all of which are crucial for identifying bottlenecks and performance degradation.
Understanding Soft Page Promotion in AIX
Before we dive further into how vmstat now supports page promotion statistics, let’s take a moment to understand what Soft Page Promotion actually means—especially for those who might not be familiar with it.
In AIX, Soft Page Promotion is a memory optimization technique designed to improve system performance by combining smaller memory pages into larger ones. The primary goal of this process is to reduce memory fragmentation and enhance memory access efficiency. Larger pages mean fewer TLB (Translation Lookaside Buffer) entries and better CPU cache utilization, which translates into faster access times for applications.
Now, here’s an important detail. AIX does not automatically promote pages to 16MB MPSS (Mixed Page Size Segment Support) pages on its own. Instead, this task is handled by a user-space tool called the Active System Optimizer (ASO).
The ASO daemon runs in the background and periodically scans the system's memory to identify candidate regions that would benefit from page promotion. When it finds suitable areas, it initiates the promotion process, helping to optimize memory usage without requiring manual intervention.
Here’s the kicker: while the kernel does track soft page promotion stats through its own private data structures, no tool was actively using this data (until now).
I’ve integrated this soft page promotion information into the vmstat command output. This addition can be a game-changer for performance tuning. By bringing these insights to the forefront, system admins and performance engineers can:
To make soft page promotion statistics more accessible to users, a new flag -L has been added to the vmstat command in AIX. This enhancement brings real-time visibility into how memory pages are being promoted (insight that was previously hidden deep within the kernel).
Demonstrating the new -L flag in vmstat:
- Usage Message (When Verbosity Level is not Provided)
- Standard use of -L with Verbosity Level as 1
- Combining -L with -v to report statistics maintained by Virtual Memory Manager
This new capability makes vmstat even more powerful as a one-stop shop for AIX performance monitoring. If you’re working on memory tuning or just want deeper insights into your system’s behavior, give -L flag a try and see what your pages have been upto.