000-221 · Question #217
A system with multiple applications is experiencing bursts of activity. This drives the free pages list very low, resulting in increased wait times for applications. Given the vmstat output below…
The correct answer is D. Increase the minfree and maxfree tunables. Increasing the minfree and maxfree tunables raises the thresholds at which AIX's VMM steals pages, keeping a larger pool of free pages available to absorb memory bursts.
Question
A system with multiple applications is experiencing bursts of activity. This drives the free pages list very low, resulting in increased wait times for applications. Given the vmstat output below, what can be done to increase the number of free pages to compensate for these bursts of activity?
Exhibit
Options
- AIncrease the maxpin tunable.
- BIncrease the page space size.
- CIncrease the lru_file_repage setting.
- DIncrease the minfree and maxfree tunables
How the community answered
(19 responses)- A5% (1)
- B16% (3)
- C5% (1)
- D74% (14)
Why each option
Increasing the minfree and maxfree tunables raises the thresholds at which AIX's VMM steals pages, keeping a larger pool of free pages available to absorb memory bursts.
The maxpin tunable controls the maximum number of pages that can be pinned (locked) in real memory, and adjusting it does not directly increase the size of the free pages list.
Increasing page space expands virtual memory available for paging out, but does not raise the real-memory free-page thresholds that govern how aggressively the VMM reclaims pages.
The lru_file_repage tunable governs whether file pages participate in LRU repaging, but changing it does not set the minfree/maxfree targets that control how many free pages the VMM actively maintains.
The minfree tunable sets the minimum free-page count that triggers the VMM's page-stealing daemon (lrud), and maxfree sets the target level at which stealing stops. Increasing both values causes the VMM to reclaim pages more aggressively and earlier, ensuring a consistently larger free-page buffer is maintained to handle sudden spikes in application memory demand without driving wait times higher.
Concept tested: AIX VMM minfree and maxfree tunable configuration
Source: https://www.ibm.com/docs/en/aix/7.3?topic=performance-tuning-virtual-memory-manager
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