aio_iosize_max(5)aio_iosize_max(5)NAMEaio_iosize_max - maximum size of any asynchronous I/O in an lio_lis‐
tio(), aio_read(), or aio_write() call
This tunable places a limit on the size (in bytes) of asynchronous I/O
operations that can be issued with lio_listio(2), aio_read(2), or
aio_write(2). It is useful for limiting the amount of memory that can
be consumed by asynchronous I/O operations.
When this tunable is at its default value of 0, it has no effect.
When this tunable is set to a positive number, all asynchronous I/Os of
size larger than that number will fail with Although this tunable will
affect all applications that use asynchronous I/O, its most common
usage is in conjunction with This combination is useful for limiting
the system resources that can be used by applications that use
Who Is Expected to Change This Tunable?
System administrators that run applications requiring heavy usage of
AIO to disks or filesystems.
Restrictions on Changing
This tunable is dynamic. Changes to to this tunable take effect imme‐
diately after the change. All processes on the system will be immedi‐
ately impacted, including processes already running.
When Should the Value of This Tunable Be Raised?
should be raised for applications requiring heavy use of asynchronous
What Are the Side Effects of Raising the Value of This Tunable?
When raising the value of this tunable from 0 to any positive value,
the limit defined by this tunable will begin to be enforced. (See
However, once this tunable is a positive value, the only effect of
raising it further is that larger I/Os can be issued by applications.
Limits such as will continue to be enforced after this tunable is set.
(Unless aio_proc_max(5) has already been used to disable them)
When Should the Value of This Tunable Be Lowered?
should be lowered when POSIX AIO performance is acceptable but there is
concern about buggy or malicious applications issuing excessively large
I/Os that tie up system resources. When this tunable is non-zero, its
value should never be lower than the minimum I/O size required by
trusted applications running on the system.
What Are the Side Effects of Lowering the Value of This Tunable?
As long as it remains a positive value, lowering the value of this tun‐
able simply reduces the maximum possible size of asynchronous I/Os.
When this tunable is set to 0, it will cease to have an effect, and no
limits will be imposed on the size of individual asynchronous I/Os.
What Other Tunables Should Be Changed at the Same Time as This One?
No other tunables need to be changed at the same time as this one.
However, the most common usage is for this tunable to be used in con‐
junction with In this way, the total memory usage of all processes that
use aio_reap(2) is constrained by the quantity:
All HP-UX kernel tunable parameters are release specific. This parame‐
ter may be removed or have its meaning changed in future releases of
Installation of optional kernel software, from HP or other vendors, may
cause changes to tunable parameter values. After installation, some
tunable parameters may no longer be at the default or recommended val‐
ues. For information about the effects of installation on tunable val‐
ues, consult the documentation for the kernel software being installed.
For information about optional kernel software that was factory
installed on your system, see at
was developed by HP.
SEE ALSOkctune(1M), sam(1M), gettune(2), settune(2), aio_reap(2), aio_read(2),
aio_write(2), lio_listio(2), aio_physmem_pct(5), aio_proc_max(5).
Tunable Kernel Parameters aio_iosize_max(5)