Swap Memory- problem

[Tvs]

The server giving memory utilization is high – Tivoli alert
The total physical memory in the dmesg output is 38gb
Whereas in swapinfo the memory is showing only 32. .and in reserved memory it showing available is nil. And used is 20480 Mb. can any one explain how it is calculating...


swapinfo -tm
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 1024 0 1024 0% 0 - 1 /dev/vg00/lvol2
dev 7168 0 7168 0% 0 - 1 /dev/vg00/lvol9
dev 12288 0 12288 0% 0 - 1 /dev/vg00/lvol14
reserve - 20480 -20480
memory 32813 29468 3345 90%
total 53293 49948 3345 94% - 0 -



#dmesg
Memory Information:
physical page size = 4096 bytes, logical page size = 4096 bytes
Physical: 41811968 Kbytes, lockable: 33534464 Kbytes, available: 38470524 Kbytes


Glance Output
-------------------------

Event Current Cumulative Current Rate Cum Rate High Rate
--------------------------------------------------------------------------------
Page Faults 2303 6142 451.5 365.5 1898.5
Page In 668 1946 130.9 115.8 701.4
Page Out 0 0 0.0 0.0 0.0
KB Paged In 0kb 0kb 0.0 0.0 0.0
KB Paged Out 0kb 0kb 0.0 0.0 0.0
Reactivations 0 0 0.0 0.0 0.0
Deactivations 0 0 0.0 0.0 0.0
KB Deactivated 0kb 0kb 0.0 0.0 0.0
VM Reads 0 0 0.0 0.0 0.0
VM Writes 0 2 0.0 0.1 0.3

Total VM : 45.6gb Sys Mem : 4.43gb User Mem: 28.7gb Phys Mem: 39.9gb
Active VM: 11.3gb Buf Cache: 1.59gb Free Mem: 5.17gb

[RAC_1 · Accepted solution]

When you get memory line is swapinfo, you have set kernel tunable swapmem_on to 1. This is done so that kernel calculates the memory as swap space configured + 75% of RAM

This is just for kernel calculation of available memeory and proves helpful with large RAM systems.

You buffer cahe looks quite high. What type of buffer cahe you use?? Static (use of bufpages kernel setting) or dynamic (dbc_pct_max and dbc_pct_min)

Is it effectively used?? - sar -b 2 3, if %write hit value is not about 90 or so, it is not effectively used. You may want to set to about 800MB or so. (Depends upon what you are running on the system)

[Devender Khatana]

Hi,

Everything looks fine in the outputs. Glance also is reporting the memory to be 39.9Gb which is same as through dmesg.

Do not get confused from the output of swapinfo.

Also the buffer cache is OK as it is only 4% of available total memory which is quite usual.

HTH,
Devender

[CAS_2]

Unless buffer-cache be too high, I think the high percentage value given by swapinfo is due that the SWAP SPACE is smaller than the PHYSICAL MEMORY.

The physical memory in your box is 40 GB, whereas the swap space is 20 GB. And all this space space is allocated ('reserve' line shown by swapinfo command).
One swap space is allocated, system uses memory as swap. This makes increase the percentage in 'memory' line shown by swapinfo command.

Do you want to decrease that value ?

Add more swap space (keep in mind that maxswapchunk kernel parameter shoud be wide enough).

[Ted Buis]

Your swap chunks value (kernel parameter) should be checked to make sure it is large enough to address total virtual memory.