[Solved]Memory size decreasing... (Xen)

[mattV]

Hi,

I own a Dell PowerEdge 860 which has 4 GB of Memory.
Gentoo (x86_64) is installed on it and runs almost perfectly. Almost, because I encounter a very annoying problem : the size of the memory decreases after some time (I cannot say exactly after how much time, some hours or days).

When I reboot, everything's fine again, the right amount of memory is there.

Here's the information given by top and /proc/meminfo

After a fresh reboot :

top - 20:04:08 up 3 min, 2 users, load average: 0.01, 0.02, 0.00
Tasks: 57 total, 2 running, 55 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0% us, 0.0% sy, 0.0% ni, 100.0% id, 0.0% wa, 0.0% hi, 0.0% si
Mem: 3983236k total, 214732k used, 3768504k free, 2916k buffers
Swap: 506008k total, 0k used, 506008k free, 20892k cached

MemTotal: 3983236 kB
MemFree: 3769036 kB
Buffers: 2888 kB
Cached: 20836 kB
SwapCached: 0 kB
Active: 34260 kB
Inactive: 8016 kB
SwapTotal: 506008 kB
SwapFree: 506008 kB
Dirty: 408 kB
Writeback: 0 kB
AnonPages: 18664 kB
Mapped: 4552 kB
Slab: 12552 kB
SReclaimable: 4300 kB
SUnreclaim: 8252 kB
PageTables: 928 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
CommitLimit: 2497624 kB
Committed_AS: 97808 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 600 kB
VmallocChunk: 34359737535 kB


Later :


top - 19:56:38 up 2 days, 22:18, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 59 total, 2 running, 57 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0% us, 0.0% sy, 0.0% ni, 100.0% id, 0.0% wa, 0.0% hi, 0.0% si
Mem: 1623040k total, 1612800k used, 10240k free, 175616k buffers
Swap: 506008k total, 0k used, 506008k free, 963520k cached


MemTotal: 1623040 kB
MemFree: 10108 kB
Buffers: 175616 kB
Cached: 963520 kB
SwapCached: 0 kB
Active: 192476 kB
Inactive: 968292 kB
SwapTotal: 506008 kB
SwapFree: 506008 kB
Dirty: 8 kB
Writeback: 0 kB
AnonPages: 21724 kB
Mapped: 4360 kB
Slab: 292592 kB
SReclaimable: 275388 kB
SUnreclaim: 17204 kB
PageTables: 844 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
CommitLimit: 1317528 kB
Committed_AS: 116516 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 632 kB
VmallocChunk: 34359737535 kB


Kernel :

2.6.20-xen-r6 #1 SMP Thu Oct 18 22:30:22 CEST 2007 x86_64 Intel(R) Xeon(R) CPU 3060 @ 2.40GHz GenuineIntel GNU/Linux


It droped from 4 GB to 1,6 GB !

Any idea what this strange problem is due to ?


Thank you.

[mattV]

Working with Xen, I think this behavior is normal.

It must be related to Xen and its "balloon memory" techniques.

Actually, I observed that the memory that is displayed when I do a "cat /proc/meminfo" is the memory that is still available for the hypervisor.

The /proc/meminfo matches the Mem of Dom0 given in the output of "xm list" :