aio_physmem_pct
aio_physmem_pct specifies the maximum percentage of the
total physical memory in the system that can be locked for use in POSIX
asynchronous I/O operations.
5
50
10
Specify integer value. For more information, see Specifying Parameter Values.
This parameter places a limit on how much system memory can be locked by
the combined total number of POSIX asynchronous I/O operations that are
in progess at any given time. It is also important to be aware that an
operation remains on the active queue and memory is not released, even
if the operation is complete, until it is properly terminated by an
aio_return() call for that operation.
Asynchronous I/O operations that use a request-and-callback mechanism
for I/O must be able to lock the memory they are using. The
request-and-callback mechanism is used only if the device drivers
involved support it. Memory is locked only while the I/O transfer is in
progress. On a large server it is better to increase
aio_physmem_pct to higher values (up to 50).
aio_physmem_pct imposes a system-wide limit on lockable
physical memory. A per-process lockable-memory limit can also be
self-imposed by using the setrlimit() system call within
the application program (see HP-UX Reference entry
setrlimit(2)).
Remember too that the total amount of memory that can be locked at any
given time for any reason, not just for asynchronous I/O, is controlled
by the system-wide limit lockable_mem. Other system
activity, including explicit memory locking with plock() and/or mlock()
interfaces can also affect the amount of lockable memory at any given
time.
There is no kernel parameter named lockable_mem, but there
is a parameter named unlockable_mem which affects it. The
value of lockable_mem is determined by subtracting the
value of unlockable_mem from the amount of system memory
available after system startup. During startup, the system displays on
the system console the amount of its lockable memory (along with
available memory and physical memory). These values can be retrieved
while the system is running by using the /sbin/dmesg
command.
For more information about POSIX asynchronous I/O, see the HP-UX
Reference entry aio(5). Also refer to the system
memory-management whitepaper available on the system in file
/usr/share/doc/mem_mgt.txt. Other whitepapers about system
management concepts also reside in the same directory.
The amount of memory that can be locked under the limit imposed by
aio_physmem_pct cannot exceed the total system-wide
lockable-memory limit imposed by
unlockable_mem.