NAME
maxswapchunks — maximum number of swap chunks which can be managed by swap system
VALUES
Allowed values
Minimum: 1 chunk
Maximum: 16384 chunks
A swap chunk is a collection of 1 KB blocks (the exact size
is determined by the tunable
swchunk).
DESCRIPTION
Swap space in the kernel is managed using 'chunks' of either physical
device space or file system space.
These chunks are used as the indices on the first layer of the
two-layer swap table.
Address offsets are then used to find the position within the
current chunk, providing the second layer of indexing.
This two-layer schema allows the swap table to be kept relatively
small, as opposed to a large table indexed directly by swap
page.
maxswapchunks
controls the size of the global swap table, setting the upper limit on
the number of swap chunks accessible by the system.
Who is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
When Should the Value of This Tunable Be Raised?
This tunable should be raised if more swap is present than the present
table can accommodate.
The kernel checks for this condition when adding swap (either on
boot or during runtime) and prints a console message:
Unable to add all swap from <device or file system>.
Increase the tunable parameter maxswapchunks by < X >
and re-configure your system.
All the swap possible (however many swap chunks
are left in the table) will be added to the system in the above
scenario.
If no more swap will be added after the device triggering this
message, adding X as stated in the message (presuming this is
still below the maximum of 16384) will suffice.
If more swap will be added, the customer should add sufficiently
to accommodate all the needed chunks.
To calculate the number of needed chunks, divide the device size
by the value of tunable
swchunkS
* 1024 bytes.
If the maximum of
maxswapchunks
is reached, but
swchunkS
is below the maximum,
swchunkS
should be raised and the required
maxswapchunks
should be recalculated.
What Are the Side Effects of Raising the Value?
The kernel will use more memory for the larger swap table.
When Should the Value of This Tunable Be Lowered?
The tunable should only be lowered if it is significantly higher
than the amount of chunks which will be used on the system, and
physical memory is at a premium.
What Are the Side Effects of Lowering the Value?
Future swap additions may partially fail due to insufficient chunks
as previously described.
What Other Tunable Values Should Be Changed at the Same Time?
swchunk
should be considered when modifying
maxswapchunks.
swchunk
sets the size of a swap chunk in 1024 byte pages, so increasing
the chunk size yields less chunks needed in the table (and a
smaller needed maxswapchunks) for a given swap space.
Similarly, lowering swchunk means that more chunk indices in
the swap table will be needed.
WARNINGS
All HP-UX kernel tunable parameters are release specific.
This parameter may be removed or have its meaning changed in
future releases of HP-UX.
AUTHOR
maxswapchunks
was developed by HP.
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