swap and paging

[Darren Murray_1]

Hi,
Here is a snapshot of our system.

what would you suggest is happening on the machine?

With sudo swap enabled i thought it had to reach 100% before hitting device swap

TYPE AVAIL USED FREE USED
dev 800 116 684 14% /dev/vg00/lvswap
dev 200 116 84 58% /dev/vg00/lvswap2
reserve -513 -513
memory 540 195 345 36%
total 1540 940 600 61%

[Ashwani Kashyap]

When a process starts HPUX reserves swap space for it , in case it needs it . Thats what you are seeing . It might not be necessarily swapping or paging , but the space is just reserved .

Actull paging utilisation can be found put with glance . You can actually see ho many page faults are occuring and which process is doing that .

[V.Tamilvanan]

Hi,

Check by sar -w . If there are lot of swapouts then you need check for increasing the RAM.

[Bharat Katkar]

Hi there,
You can also use
#vmstat
to monitor whether paging is happening or not and how page faults are occuring.
It will also give other virtual memory related statistics.

Hope that helps.
Regards,

[Jose Mosquera]

Hi,

Pls check the swapper presence on top 1st page, if be there your system handles activation and reactivation of processes when free memory falls bellow minfree, or when the system appears to be ???trashing???.

dbc_max_pct Kernel parameter fix this problem, the recomendations are from 5% to 10% depends on the total amount of memory in your system.

The minimun value must be 300MB, then you can try to put a low percentage, I sugest you that first try with 25% and look at the backup performance in order to know if this is a good percentage. After you do this and reboot your dont want to see the USED line for the device lines from swapinfo -mt > 0. This means no memory pressure and no paging. This will increase performance considerably.

Rgds.

[Trond Haugen]

With vmstat and 'sar -w' what you should watch out for is page outs (po) or swap outs (swpot/s) as that starts to occure when there is memory preasure on the system.

Regards,
Trond

[Ted Buis]

You still want to have as much or more swap space as RAM, as pseudo swap is not really very good to use. Also, make sure your max_swap_chunks parameter is large enough to cover the full swap area.