Tuning minfree and maxfree (free memory pages)

If a process has to wait for memory pages, system performance is impacted. The system keeps a pool of available pages just for this. To see if we need to adjust minfree and maxfree, first find out what they are set to now:

AIX 4

/usr/samples/kernel/vmtune

AIX 5

vmo -o minfree
vmo -o maxfree 

Then, run vmstat and watch the fre column. If the fre column reaches minfree, raise the minfree and maxfree parameters. If the fre colum is consistantly above maxfree, then no tuning is necessary.

AIX 4

/usr/samples/kernel/vmtune -f 120 -F 128

AIX 5

vmo -p -o minfree=120
vmo -p -o maxfree=128 

AIX 5.3+

vmo -p -o minfree=960
vmo -p -o maxfree=1088 

NOTE: Cerner recommends minfree = 120 * # CPUs and maxfree = minfree + ( 8 * # of CPUs) for AIX up to 5.3.

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