# [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.Last edited by mattV on Sun Dec 09, 2007 9:29 am; edited 1 time in total

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## 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" : 

```

abc ~ # xm list

Name      ID   Mem    VCPUs   State   Time(s)

Domain-0   0   1581   2   r-----   1053.7

vm1      2   128   1   -b----   37.2

vm2      6   768   1   -b----   4.7

vm3      5   1536   1   -b----   5.2

```

Indeed, when I start another vm, with, let say 1024 MB RAM, according to the /proc/meminfo, the server only has 250MB of RAM...

It's a bit strange but I'm glad it seems to be normal.

Correct me if I'm wrong

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