HP-UX HB v13.00 Ch-22 - Performance and Tuning

HP-UX Handbook – Rev 13.00 Page 9 (of 19)
Chapter 22 Performance & Tuning
October 29, 2013
first area to check. To determine virtual memory configuration run the following command:
Tools for monitoring memory allocation
To determine the amount and usage of swap, the swapinfo command can be executed:
# swapinfo –tam
Mb Mb Mb PCT START/ Mb TYPE
AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 8192 0 8192 0% 0 - 1 /dev/vg00/lvol2
dev 8192 0 8192 0% 0 - 1 /dev/vg00/lvol9
dev 34520 0 34520 0% 0 - 1 /dev/vg13/lvol1
reserve - 31358 -31358
memory 49020 21337 27683 44%
total 99924 52695 47229 53% - 0 –
The fields represent:
dev -Paging space residing on a mass storage device. The Used amount reflects only what is
being paged to disk .
reserve – Process paging space on reserve. Upon fork the estimated size in memory for a process
is locked in this pool until process termination This is only true of device swap .
memory -also known as pseudo-swap . This area of RAM is used for direct memory access for
on processor memory calls and when device swap is exhausted to serve as process reserve
memory.
At system startup ,swapspc_cnt and swapmem_cnt are initialized to the total amount of swap
space and pseudo-swap available, i.e. swapspc_max and swapmem_max respectively.
Any time the swapon call is made swapspc_cnt is adjusted by the amount of swap added.
A process reserves swap simply by decrementing these two counters.
The kernel doesn't actually use disk blocks until they are needed. Device swap is used first, until
swapspc_cnt=0 . When a process actually has to allocate swap the system knows it has enough
room to do so as it has been allocated at the time of the fork call.
If there is no device or file system swap available , the system allocates pseudo-swap as a last
resort. It decrements swapspc_cnt and keeps track of regions using pseudo-swap via a
pswaplist. Pseudo-swap is either free or pseudo-allocated , it is never reserved.