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

Chapter 1 7
1 Introducing HP-UX Memory File
System (MemFS) 1.0
This chapter introduces you to the HP-UX implementation of Memory File System (MemFS).
The following topics are discussed:
•Overview
• Need for a Memory-Based File System
• Architecture of HP-UX Memory File System
• Application Areas for HP-UX Memory File System
•Dependencies
Overview
A Memory-based File System (MemFS) is a file system that resides in memory. It does not
normally write data out to stable storage. A MemFS is created from a mount operation, and
ceases to exist when it is un-mounted. The purpose of such a file system is to provide fast
access for temporary files that do not need to be kept for an indeterminate time. Because it
does not normally have to do I/O to stable storage, the MemFS is able to provide extremely
high throughput.
Keeping data in memory comes at a cost. It consumes system physical memory. Even with
today's large-memory systems, physical memory comes at a premium. A system or application
that runs out of available memory at a critical time can cause irreparable loss to the user. This
is the reason why most Virtual Memory (VM) management systems implement a paging
policy, wherein less frequently used memory pages are paged out to a swap device. This policy
has been extended to MemFS. Under memory pressure, the VM system can deallocate
MemFS pages and re-assign them where needed.
Unlike the MemFS on HP-UX 11iv2, the 11iv3 version of MemFS does not require a user
process to be associated with each of its instances. MemFS pages will be directly written to
system swap device under memory pressure and will be retrieved when needed.