memfs_metamax.5 (2010 09)
m
memfs_metamax(5) memfs_metamax(5)
(Tunable Kernel Parameters)
NAME
memfs_metamax - maximum amount of kernel memory used for MemFS metadata
VALUES
Failsafe
15% of kernel memory
Default
15% of kernel memory
Allowed values
Integer values:
11- 30% of kernel memory
DESCRIPTION
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 accom-
modate 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.
Values can be specified as follows:
1) Default.
2) A percentage of total kernel memory:
A positive whole number followed by a percent symbol (for example, 10%).
3) A constant value:
A positive whole number that represents number of bytes of kernel memory, optionally followed
by a multiplier suffix, where
K=1000, KB=1024, M=
1000000, MB=(1024*1024), and
GB=(1024*1024*1024)
. For example, a constant value could be 500K.
Metadata of MemFS file systems is never swapped out of the memory or reused, unless the MemFS file
system is unmounted. Therefore, it is important to define a value for this tunable that balances memory
usage for MemFS and for the rest of the system.
Restrictions on Changing
The tunable should not be kept at a very high value as it may impact system performance if more memory
is consumed by MemFS. The tunable is dynamic.
When Should the Value of This Tunable Be Raised?
The value of
memfs_metamax may need to be raised on systems with a large number of files and direc-
tories in MemFS file systems. When the creation of files or mounting of new MemFS file systems fail
because the specified memory limit has been reached, the following message will be displayed on the con-
sole:
memfs: metadata exceeds memfs_metamax
When the above message is displayed, then this tunable needs to be increased.
What Are the Side Effects of Raising the Value?
Raising this value allows more kernel memory for MemFS metadata. However, this might negatively
impact system performance or performance of applications that compete for kernel memory.
When Should the Value of This Tunable Be Lowered?
The value of memfs_metamax can be lowered on systems with small or no mounted MemFS file systems.
In the case where the new limit specified is less than the memory in use by MemFS metadata (for exam-
ple, 20480 bytes), the request succeeds with following warning displayed on console:
Warning: The specified value of tunable memfs_metamax is less than the
amount of memory currently in use by MemFS, 20480 bytes
In this situation, creations of new files or mounting new file systems will fail until the metadata usage
falls below the specified value.
What Are the Side Effects of Lowering the Value?
This limits the number of files and directories that can be created in MemFS file systems. However, it
also ensures more kernel memory for system performance and other applications.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1