Maximum caching of file data tuning
NFS does not have its own dedicated buffers for caching data from files in NFS-exported file systems.
Instead, the Virtual Memory Manager (VMM) controls the caching
of these file pages. If a system acts as a dedicated NFS server, it might
be appropriate to permit the VMM to use as much memory as necessary for data
caching. For a server exporting JFS file systems, this is accomplished by
setting the maxperm parameter, which controls the
maximum percentage of memory occupied by JFS file pages to 100 percent. This
parameter is set using the vmo command. For example:
# vmo –o maxperm%=100
On a server exporting Enhanced JFS file systems, both
the maxclient and maxperm parameters
must be set. The maxclient parameter controls the
maximum percentage of memory occupied by client-segment pages which is where
Enhanced JFS file data is cached. Note that the maxclient value
cannot exceed the maxperm value. For example:
# vmo –o maxclient%=100
Under certain conditions, too much file data cached in memory might actually be undesirable. See File system performance for an explanation of how you can use a mechanism called release-behind to flush file data that is not likely to be reused by applications.