The maxpin% value specifies the maximum percentage of realmemory that can be pinned on AIX. The default value is 80 and this should onlybe changed under exceptional circumstances, usually with the involvement ofIBM.

The VxFS tuneables that affect VxFS pinned heap usageare:
vxfs_ninode:       The maximum number of inode entriescached in the inode table.
vx_bc_bufhwm:   The maximum amount of memory,in Kb, that can be used for buffers in the VxFS buffer cache.


Asmaxpin% defines the maximum amount of pinned heap memory then it may be that themaximum amount of buffer cache that is allocated may never reach vx_bc_bufhwm ifthe value of vx_bc_bufhwm is greater than the amount defined bymaxpin%.

There may be cases where it is found that VxFS is using too muchof pinned heap, preventing other processes from acquiring the pinned heap thatthey need. In those cases it is recommended to reduce the amount of pinned heapbeing used by VxFS by reducing vxfs_ninode and vx_bc_bufhwm.

To see whatthe current setting of maxpin% is run the following command:
# vmo -omaxpin%
maxpin% = 80
#

To monitor VxFS inode cache and buffercache use vxfsstat:
# vxfsstat -bi /vxfsmnt

05:18:27.917 Thu Jul 1505:18:27 2010 -- absolute sample

Lookup, DNLC & Directory CacheStatistics
  294400 maximum entries in dnlc
      27total lookups            62.96% fastlookup
      28 total dnlclookup        64.29% dnlc hitrate
       6 totalenter               1.64  hit perenter
       0 total dircachesetup      0.00  calls per setup
      11total directory scan      9.09% fast directory scan

inodecache statistics
     180 inodes current      180 peak               294270maximum
      68lookups             0.00% hitrate
     234 inodes alloced         54freed
 1479179 sec recycle age [not limited bymaximum]
    1800 sec free age

buffer cachestatistics
    1152 Kbyte current     574496maximum
     477lookups            84.70% hitrate
    3569 sec recycle age [not limited bymaximum]


Note that the maximum value in 'buffer cache statistics'will be slightly less than the value specified in vx_bc_bufhwm. Forexample:
# echo "vx_bc_bufhwm/D"|kdb_64
...
(0)> dwvx_bc_bufhwm
vx_bc_bufhwm+000000: 0009CCC6 00000010 00000000000108A6  ................
(0)>

0x9CCC8 = 642246Kb

Ascan be seen in the vxfsstat output above the value in vx_bc_bufhwm is slightlyhigher than the maximum reported for buffer cache in vxfsstat output. This isdue to the space that is reserved for buffer headers.