Checking Kernel Memory Allocation

The KMA allows a kernel subsystem to allocate and free memory, as needed.

Rather than statically allocating the maximum amount of memory it is expected to require under peak load, the KMA divides requests for memory into three categories:

• Small (less than 256 bytes)

• Large (512 bytes to 4 Kbytes)

• Oversized (greater than 4 Kbytes)

The KMA keeps two pools of memory to satisfy small requests and large requests. The oversized requests are satisfied by allocating memory from the system page allocator.

If you are checking a system that is being used to write drivers or STREAMS that use KMA resources, then the sar -k command will likely prove useful. Otherwise, you will probably not need the information it provides. Any driver or module that uses KMA resources, but does not specifically return the resources before it exits, can create a memory leak. A memory leak causes the amount of memory that is allocated by KMA to increase over time. Thus, if the alloc fields of the sar -k command increase steadily over time, there might be a memory leak. Another indication of a memory leak is failed requests. If this problem occurs, a memory leak has probably caused KMA to be unable to reserve and allocate memory.

If it appears that a memory leak has occurred, you should check any drivers or STREAMS that might have requested memory from KMA and not returned it.