Swap usage with KVM

[Daniel Bareiro <daniel-listas@gmx.net>]

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Hi all!

I have an installation with Debian GNU/Linux 5.0.4 amd64 with qemu-kvm
0.12.3 compiled with the source code obtained from the official site of
KVM and Linux 2.6.32.12 compiled from source code of kernel.org. All
this is installed on an HP Proliant DL380 G6 with two Xeon E5530
quadcore processors and 16 GiB of RAM which has two VMs with the
following configuration of memory:

Hostname       |      RAM
===============+===============
Aps4           |    7 GiB
Leela          |    7 GiB
===============+===============
TOTAL          |   14 GiB

Initially the host was created with a swap partition of 1 GiB, but today
we found that the use of swap quickly began to grow increasingly.
Therefore, as a contingency, we had to hot-add a logical volume of 1 GB
of swap on the VMHost. Is 'normal' this use of memory?

I copy the Nagios Service Log Entries for the VMHost:

Event Start Time        Event End Time  Event Duration  Event/State Type        Event/State
Information
---------------------------------------------------------------------------------------------------
06-07-2010 00:00:00     07-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
100% free (956 MB out of 956 MB)
07-07-2010 00:00:00     08-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
100% free (956 MB out of 956 MB)
08-07-2010 00:00:00     08-07-2010 16:41:43     0d 16h 41m 43s  SERVICE OK (HARD)       SWAP OK -
100% free (956 MB out of 956 MB)
09-07-2010 00:00:00     10-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
99% free (939 MB out of 956 MB)
10-07-2010 00:00:00     11-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
79% free (754 MB out of 956 MB)
11-07-2010 00:00:00     11-07-2010 07:08:17     0d 7h 8m 17s    SERVICE OK (HARD)       SWAP OK -
51% free (482 MB out of 956 MB)
11-07-2010 07:08:17     11-07-2010 10:41:07     0d 3h 32m 50s   SERVICE WARNING (HARD)  SWAP WARNING
- 29% free (272 MB out of 956 MB)
11-07-2010 10:41:07     11-07-2010 10:45:57     0d 0h 4m 50s    SERVICE CRITICAL (HARD) SWAP
CRITICAL - 9% free (83 MB out of 956 MB)
---------------------------------------------------------------------------------------------------

I'm not using qcow2 files. The /dev/cciss/c0d0p3 partition is a physical
volume that maintains the logical volumes that are used for VM's disks.

The Nagios Service Log Entries for VMs shows no excessive use of swap in
the window of time when the problem occurred in the VMHost:

Aps4:

Event Start Time        Event End Time  Event Duration  Event/State Type        Event/State
Information
---------------------------------------------------------------------------------------------------
06-07-2010 00:00:00     07-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
100% free (2850 MB out of 2863 MB)
07-07-2010 00:00:00     08-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
98% free (2797 MB out of 2863 MB)
08-07-2010 00:00:00     08-07-2010 16:41:43     0d 16h 41m 43s  SERVICE OK (HARD)       SWAP OK -
99% free (2812 MB out of 2863 MB)
09-07-2010 00:00:00     10-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
98% free (2784 MB out of 2863 MB)
10-07-2010 00:00:00     11-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
97% free (2754 MB out of 2863 MB)
11-07-2010 00:00:00     11-07-2010 11:53:38     0d 11h 53m 38s+ SERVICE OK (HARD)       SWAP OK -
100% free (2839 MB out of 2863 MB)
---------------------------------------------------------------------------------------------------

Leela:

Event Start Time        Event End Time  Event Duration  Event/State Type        Event/State
Information
---------------------------------------------------------------------------------------------------
06-07-2010 00:00:00     07-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
97% free (919 MB out of 956 MB)
07-07-2010 00:00:00     08-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
97% free (920 MB out of 956 MB)
08-07-2010 00:00:00     08-07-2010 16:41:43     0d 16h 41m 43s  SERVICE OK (HARD)       SWAP OK -
97% free (920 MB out of 956 MB)
08-07-2010 17:01:36     08-07-2010 17:04:16     0d 0h 2m 40s    SERVICE CRITICAL (HARD) Connection
refused by host
08-07-2010 17:04:16     09-07-2010 00:00:00     0d 6h 55m 44s   SERVICE OK (HARD)       SWAP OK -
97% free (921 MB out of 956 MB)
09-07-2010 00:00:00     10-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
97% free (921 MB out of 956 MB)
10-07-2010 00:00:00     11-07-2010 00:00:00     1d 0h 0m 0s     SERVICE OK (HARD)       SWAP OK -
97% free (921 MB out of 956 MB)
11-07-2010 00:00:00     11-07-2010 11:58:29     0d 11h 58m 29s+ SERVICE OK (HARD)       SWAP OK -
97% free (921 MB out of 956 MB)
---------------------------------------------------------------------------------------------------



Unfortunately I could not take much more data because we had to act
quickly, but if you need any additional information, please feel free to
ask.

Thanks in advance for your replies.

Regards,
Daniel
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