MemFS v2 û A Memory-based File System on HP-UX 11i v2

Recommended Use

Applications that will benefit most from MemFS are those that perform mostly meta-data intensive

operations like creates and deletes of small files and directories. For example: compilers, editors and

sorting applications. MemFS never writes out meta-data for files, so there is always a performance

gain for directory and file manipulation. Applications can also interact with MemFS files using the

mmap interface. Using the mmap interface instead of the read/write interface may be required for

some applications.

Some other usage guidelines are:

• Use MemFS only for temporary files-

• Distribute the files evenly across a larger number of directories. If all files are accessed

simultaneously, limit the number of files to about 100 per directory or so.

Limitations and Future Work

MemFS uses the Hierarchical File System (HFS) as its base, and, as a result, it inherits several HFS

functions that increase usage overhead. This includes the overhead of a disk based filesystem

structure, static allocation and pre-initialization of inodes. Also, lack of kernel page-able memory in

the HP-UX kernel has created the need to have user memory to back up MemFS pages, so that they

can be transparently swapped to the system swap device.

These limitations will be addressed in a future MemFS version. Addressing these limitations will ensure

that memory resources are managed more efficiently.

Summary

MemFS shows tremendous performance advantages in comparison to memory-based file systems and

also provides significant design advantages over traditional RAM disk style file systems. MemFS

provides additional file system space, and supports UNIX file semantics while remaining fully

compatible with other filesystem types.

Since MemFS is integrated with the virtual memory sub-system, it takes advantage of the kernel’s

resource management policies, and pages used by MemFS can be reclaimed back by the system.

herein is subject to change without notice. The only warranties for HP products and

services are set forth in the express warranty statements accompanying such

products and services. Nothing herein should be construed as constituting an

additional warranty. HP shall not be liable for technical or editorial errors or

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trademark of The Open Group.

4AA0-xxxxENW, August 2007