Question about swap

[Subentu]

Guys,

I have a Rx7620 system running HP-UX 11.23

This is the memory utilization of the system during the peak workload (taken using kmeminfo):

Physical memory = 4183868 16.0g 100%
Free memory = 30012 117.2m 1%
User processes = 3399628 13.0g 81% details with -user
System = 739281 2.8g 18%
Kernel = 530089 2.0g 13% kernel text and data
Dynamic Arenas = 249295 973.8m 6% details with -arena
vx_buffer_cache = 76512 298.9m 2%
vx_global_pool = 26964 105.3m 1%
VFD_BT_NODE = 23976 93.7m 1%
vm_pfn2v_arena = 16636 65.0m 0%
SWAP_MISC_ARENA = 16526 64.6m 0%
Other arenas = 88681 346.4m 2% details with -arena
Super page pool = 9504 37.1m 0% details with -kas
Static Tables = 209118 816.9m 5% details with -static
pfdat = 98063 383.1m 2%
nbuf = 54400 212.5m 1% bufcache headers
vhpt = 32768 128.0m 1%
bufhash = 8192 32.0m 0% bufcache hash headers
text = 6402 25.0m 0% vmunix text section
Other tables = 9292 36.3m 0% details with -static
Buffer cache = 209192 817.2m 5% details with -bufcache
UFC file mrg = 0 0.0b 0%
UFC meta mrg = 0 0.0b 0%



And this is the # swapinfo -tam output at the same time:

Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 4096 2049 2047 50% 0 - 1 /dev/vg00/lvol2
dev 12000 2051 9949 17% 0 - 1 /dev/vg00/lvol10
dev 16500 2049 14451 12% 0 - 1 /dev/vgswap/lvol1
reserve - 13754 -13754
total 32596 19903 12693 61% - 0 -

(outputs are attached also, if they are not clear)

My question is it normal that the free memory is so low (1%) when there is only 50% of the swap is used ?

Thanks in advance.

[Dennis Handly · Accepted solution]

You should immediately enable swapmem_on(5), why was it turned off?

>is it normal that the free memory is so low (1%) when there is only 50% of the swap is used?

There is no direct connection between swap used and free memory, if you are using more swap than memory.
The whole purpose of HP-UX is to use all of memory as possible and not use device swap.
13 Gb is for users, out of 16 Gb.

Any particular problem you are trying to solve?

[Avinash20]

If you are facing any performance issue, then I would advise to increase the physical memory or decrease the load on the users on this server.
User processes = 3399628 13.0g 81% details with -user

# ./kmeminfo -user
<< to get list of user processes consuming physical memory >>

[Emil Velez]

The reason you are using swap is because you are using all of your physical memory.

I would consider setting dbc_max at 2-3 %
That will free up physical memory without impacting the system much


or you need more physical memory.

[Venkatesh BL]

You could use kmeminfo -user to see details of the processes using that much memory. See if all is in order.

[Bill Hassell]

> is it normal that the free memory is so low (1%) when there is only 50% of the swap is used?

Of course this is normal. Swap is not used until you run out of memory. Without all the details, you can be using 1% of swap when 100% of memory is used. You are using a *LOT* of swap space and this implies that you are short of memory. Verify this by running vmstat 1 5 when the system is running slowly. The column po (page out) indicates how bad you need memory. Single numbers are fine, 2 digits up to 20-30 are OK but over 50 means you are wasting a lot of time waiting for pages to be swapped in/out.

Swap and performance are opposites -- swap allows you to run with limited memory, as long as you can wait for slow processing.