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 220
MemFS file systems have huge data, can reduce the amount of swap space available to other
applications and will negatively impact system performance or applications might fail
because of low swap condition.
The value of memfs_swapmax_pct may need to be raised on systems with a large amount of
data used for MemFS file systems. Writing of data to a file in MemFS file system fails with
error [ENOSPC] when the swap usage has reached the limit; in addition, the following
message will be displayed on the console:
memfs: Cumulative data exceeds memfs_swapmax_pct
This tunable can be modified dynamically. If the new limit specified is less than the swap
space in use by MemFS (for example 10%), following warning will be displayed on console:
Warning: The specified value of tunable memfs_swapmax_pct is less than the
percentage of swap space currently in use by MemFS, 10 percent.
NOTE The memfs_metamax and memfs_swapmax_pct tunables are dynamic on HP-UX
11i v3 and can be modified without a system reboot.
Tuning memfs_metamax and memfs_swpmax_pct to a value less than the
current usage is not immediate always, though tunables are set with the new
value, the current usage may be more than the newly specified value. However,
any operations that try to allocate resources (kernel memory and system swap)
will fail if the request goes beyond the limit imposed by current value of the
tunables.
Tools Support to Report MemFS Statistics
Tools sar(1m) and GlancePlus have been enhanced to provide the MemFS statistics such as
cumulative memory and swap space consumed by all the instances of MemFS. These tools
report memory/swap consumed in terms of 4096 bytes (4KB) only, even if base_pagesize(5)
tunable is tuned to higher values.
sar(1m)
SAR-MEMFS product reports MemFS statistics using sar(1M) command. The SAR-MEMFS
product provides a new option, -z that enables the sar(1M) command to report MemFS data.
The -z option supports the following parameters:
• blkcnt
Specifies the number of MemFS blocks in the memory.