Topics: AIX, Performance, System Admin

AIX memory consumption

The command svmon -G can be used to determine the actual memory consumption of a server. To determine if the memory is over-committed, you need to divide the memory-virtual value by the memory-size value, e.g.:

# svmon -G
               size       inuse        free         pin     virtual
memory      5079040     5076409        2631      706856     2983249
pg space    7864320       12885

               work        pers        clnt       other
pin          540803           0        2758      163295
in use      2983249           0     2093160

PageSize   PoolSize      inuse       pgsp        pin    virtual
s   4 KB          -    4918761      12885     621096    2825601
m  64 KB          -       9853          0       5360       9853
In this example, the memory-virtual value is 2983249, and the memory-size value is 5079040. Note that the actual memory-inuse (5076409) is nearly the same as the memory-size (5079040) value. This is simply AIX caching as much as possible in its memory. Hence, the memory-free value is typically very low, 2631 in the example above. As such, determining the memory size based on the memory-free value does not provide a good interpretation of the actual memory consumption, as memory typically includes a lot of cached data.

Now, to determine the actual memory consumption, divide memory-virtual by memory-size:
# bc
scale=2
2983249/5079040
.58
Thus, the actual memory consumption is 58% of the memory. The size of the memory is 5079040 blocks of 4 KB = 19840 MB. The free memory is thus: (100% - 58%) * 19840 MB = 8332 MB.

Try to keep the value of memory consumption less than 90%. Above that, you will generally start seeing paging activity using the vmstat command. By that time, it is a good idea to lower the load on the system or to get more memory in your system.



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