TUNING: fre, minfree, and maxfree relationship

UNIX AIX
1

Here's a good question about tuning. Why does my system continuously scan (sr) to free up pages when the amount of "fre" pages is well ABOVE my minfree and maxfree settings:

$ vmo -a | grep free
               maxfree = 2560
               minfree = 2048
$

Here is sample output from a "vmstat -Itw 1" command:

   kthr            memory                         page                       faults                 cpu             time  
----------- --------------------- ------------------------------------ ------------------ ----------------------- --------
  r   b   p        avm        fre    fi    fo    pi    po    fr     sr    in     sy    cs us sy id wa    pc    ec hr mi se
  5   0   0    1989487       5587  4443  1774     0     5  1492   3684  5980  78869 21788 73 12 13  2  2.80  93.4 10:16:23
  5   1   0    1989487       5670  4217  1037     0     4   873   2002  5745  75376 19430 75 11 11  2  2.84  94.7 10:16:24
  2   2   0    1989487       5640  4493   913     4     2   806   1132  5680  73061 18718 69 11 17  3  2.66  88.6 10:16:25
  4   1   0    1989487       5665  4177  1428     1     7  1075   3309  6062  75888 20405 80 12  7  1  3.00 100.1 10:16:26
  4   1   0    1989487       5658  4130   924     4    15   678   4199  5802  78884 19338 70 12 16  2  2.70  90.0 10:16:27
  3   0   0    1989487       5639  4487  1002     0     5   777   3375  5877  79213 20233 78 12  9  1  2.93  97.8 10:16:28
  2   2   0    1989487       5585  4493  1852     1     6  1419   3979  6225  77220 21150 76 13  9  2  2.90  96.8 10:16:29
  4   1   0    1989487       5361  4444  1049     0     8   914   1291  6304  88256 21985 71 13 15  2  2.76  91.9 10:16:30
  3   1   0    1989487       5633  4335  1038     1     8   782   1023  6040  80653 20273 80 12  7  1  2.98  99.5 10:16:31

I have been working with IBM and they suggested creating another paging space. That is just poopy talk because I don't want more paging space. I want it to quit scanning and work like it is suppose to! From what I understand it is NOT suppose to start scanning until the "fre" is less than the "minfree" and then it is suppose to scan and steal pages till the "fre" is equal to or greater than the "maxfree". Anyone have any ideas?

2

We finally upgraded to AIX 5.3 TL6 SP1 and now the system no longer pages like crazy. It hasn't grown from 1% for two days. Usually by now, it is up around 15%.

However, the system still constantly scans (sr in vmstat) even though our max_free is set at 2500 and there are usually around 6,000 free. Strange. I guess I'm just glad the thing quit paging. I'd still like to know how the numbers relate between minfree, maxfree, and fre. I don't think they have a 1-to-1 relationship.

3

I finally figured out we have 4 shared pools of memory and the "minfree" refers to the number of free frames in each pool. Since I have four pools, I have to take the "minfre" times 4 and that is what the "sr" is trying to keep free. Shesh... IBM had a hard time figuring this out.