Memory File System (MemFS) 1.0 for HP-UX 11i v3

Installing, Configuring, Tuning, and Removing HP-UX Memory File System
Tuning Memory File System
Chapter 218
Tuning Memory File System
MemFS uses kernel memory for storing the file's metadata. Kernel memory is shared by all
the subsystems in the kernel and this memory is not page-able. Over-use of kernel memory
can bring down the performance of the system as well as the applications that compete for
kernel memory.
MemFS provides a tunable called memfs_metamax to restrict the amount of kernel memory
used by all MemFS instances.
Writing data to MemFS files result in reserving system swap space for the MemFS files. The
system swap space is a shared resource. In addition to MemFS, other applications also
consume certain amount of swap space. For example, the execution of very large programs can
be affected if MemFS file systems are huge in size. Thus the swap space needs to be used
judiciously to allow other applications to have an adequate share of it. MemFS provides a
tunable called memfs_swapmax_pct to restrict the amount swap space being used by all
MemFS instances.
memfs_metamax
The metadata of all the MemFS file systems mounted in the system is stored in kernel
memory. The memfs_metamax tunable defines the maximum percentage of kernel memory
that can be used to accommodate MemFS metadata. The tunable does not reserve or assure
the memory of specified size; it just assures that the metadata does not grow beyond the
specified size. Metadata of MemFS file systems is never swapped out of the memory or reused,
unless the MemFS file system is unmounted. The value of this tunable can be as low as 1% of
kernel memory and as high as 30% kernel memory. The default value is 15% of kernel
memory. This tunable can accept both percentage and absolute values.
Values can be specified as follows:
1. Default
Example:
kctune -s memfs_metamax=Default
2. A percentage of total kernel memory: A positive whole number followed by a percent
symbol (for example, 20%).
Example:
kctune -s memfs_metamax=20%