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We are new to AIX environment, and experiencing some performance issue running our application.

When it happens, we use the vmstat command and found the fre value under memory usually very low. A sample is as follow

System configuration: lcpu=4 mem=3920MB

kthr    memory              page              faults        cpu
----- ----------- ------------------------ ------------ -----------
 r  b   avm   fre  re  pi  po  fr   sr  cy  in   sy  cs us sy id wa
 1  2 1139816 2335   0  20  28  28  100   0  71 1914 900  3  0 94  3

The vmstat -v command displays following output.

 1003520 memory pages
  960145 lruable pages
   13197 free pages
       1 memory pools
  192564 pinned pages
    80.0 maxpin percentage
     5.0 minperm percentage
    80.0 maxperm percentage
     4.4 numperm percentage
   42287 file pages
     0.0 compressed percentage
       0 compressed pages
     4.4 numclient percentage
    80.0 maxclient percentage
   42287 client pages
       0 remote pageouts scheduled
  177501 pending disk I/Os blocked with no pbuf
 4609847 paging space I/Os blocked with no psbuf
    2484 filesystem I/Os blocked with no fsbuf
       0 client filesystem I/Os blocked with no fsbuf
     280 external pager filesystem I/Os blocked with no fsbuf
       0 Virtualized Partition Memory Page Faults
    0.00 Time resolving virtualized partition memory page faults

We found some high figure in the paging space I/Os blocked with no psbuf, and found some document from that need to find the reason why is system paging or increase size of the page datasets. But we have no ideas how to achieve that. Any advise will be greatly appreciated.

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up vote 1 down vote accepted

There's various potential causes and fixes, but essentially it's telling you that you don't have enough paging space for what you're trying to fit into the box.

You could create a second paging space, or you could try and alter the method of paging that AIX uses, by running

vmo -o lru_file_repage=0

which will make a change which will be reset on the next reboot. To make it permanent run

vmo -p -o lru_file_repage=1

There's lots you can do to AIX to tune it, but without more information on your current setup I can't really help you more. There's some good documentation on tuning AIX 5.3 here

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