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

Introducing HP-UX Memory File System (MemFS) 1.0
Architecture of HP-UX Memory File System
Chapter 110
UFC are not treated specially from the pages of other file systems. Periodically, the VM paging
algorithm reallocates the less used pages including the MemFS pages from the UFC. When
VM paging algorithm decides to reallocate MemFS pages during memory pressure, the
MemFS files data will be written directly to system swap device. When ever the files data is
needed, the data will be brought back to UFC directly from the system swap. Though HP-UX
11iv3 does not support pageable kernel memory, MemFS and UFC interact with each other to
accomplish the above tasks. Thus the HP-UX 11iv3 MemFS does not require the instance
specific user process address space for swapping the files data. The overview of MemFS
architecture is depicted in the figure shown below (see figure1).
A umount (1M) on the MemFS removes the file system and all its data. As per the
specifications, data cannot be recovered once a umount (1M) happens.
MemFS uses two main resources: kernel memory and system swap space. These resources are
shared among all the kernel subsystems and user applications. Thus there is a need to wisely
use these shared resources. MemFS provides the following tunables to limit the usage
exclusively by MemFS:
• memfs_metamax
Tunable to limit the amount of kernel memory used by MemFS
• memfs_swapmax
Tunable to limit the amount of swap space used by MemFS
For more details on these tunables, see Chapter 2, “Installing, Configuring, Tuning, and
Removing HP-UX Memory File System,” on page 15.