memfs_swapmax_pct.5 (2010 09)

m
memfs_swapmax_pct(5) memfs_swapmax_pct(5)
(Tunable Kernel Parameters)
NAME
memfs_swapmax_pct - maximum percentage of swap space allowed for MemFS
VALUES
Failsafe
50
Default
50
Allowed values
Integer values: 0 - 80
DESCRIPTION
The data of all the MemFS file systems mounted in the system is backed up by the swap device. Swap
space is reserved when the data is written to a file. The
memfs_swapmax_pct
tunable defines the
maximum percentage of space that can be used to store MemFS data. The tunable does not reserve or
assure the specified percent of swap space for MemFS; it just assures that MemFS data does not grow
beyond the specified percent. Metadata of MemFS file systems is never swapped out of the memory or
reused, unless the MemFS file system is unmounted.
Tunable values can be specified as follows:
1) Default
2) A percentage of total swap space; a positive whole number (0-80)
Data in MemFS files share the system swap device used by others. Therefore, it is important to define a
value for this tunable that balances MemFS swap usage and usage for the rest of the system. The size of
the MemFS file system will be less than what is specified by the size mount option, if there is not enough
free space available for MemFS on the system.
Restrictions on Changing
The tunable should not be kept at a very high value as it may impact system performance if more swap
space is consumed by MemFS. The tunable is dynamic.
When Should the Value of This Tunable Be Raised?
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 le 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
What Are the Side Effects of Raising the Value?
Raising this value allows more swap space for MemFS data. However, this might negatively impact sys-
tem performance or performance of applications that uses more memory.
When Should the Value of This Tunable Be Lowered?
The value of
memfs_swapmax_pct 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 swap space in use by MemFS (for
example, 10 percent), the request succeeds with following warning displayed on console:
Warning: The specified value of tunable memfs_swapmax_pct is less than
the amount of swap space currently in use by MemFS, 10 percent
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 amount of data that can exists on all the MemFS file systems cumulatively. However, it
also ensures more swap space for system performance and other applications.
What Other Tunable Values Should Be Changed at the Same Time?
None.
HP-UX 11i Version 3: September 2010 1 Hewlett-Packard Company 1

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