Re: [Xen-users] dynamic memory extension not working on Debian Squeeze

[Alexandre Kouznetsov <alk@xxxxxxxxxx>]

Hello, Ian.

I have been living with the same problem for years. I guess it worked on 
Etch with kernel 2.6.18, not sure about Lenny and 2.6.26. In my case, 
xenstore works fine.
The symptom is: after using mem-set, it apparently works, but the DomU 
still thinks it has the old memory size. The issue shows up only when 
increasing memory above the original size, the reduction work fine.
I have read the rest of the thread, and it seems Peter is stuck in some 
xenstore issue. I suspect xenstore might be unrelated: in my case it 
works fine, but mem-set still have the issue.
The OS on Dom0 and DomU is a regular Debian Squeeze, no backports or 
custom build packages. It has been seen on different models of Dell 
PowerEdge servers. If relevant, I can confirm for a commodity hardware 
case, or for a Debian Wheezy case (upgraded from Squeeze, not a clean 
install). I have no other OS at hand than Debian to test.
The output of "xenstore-ls -fp" that you asked remains unchanged, so I 
will post it only once:
root@on05:~# xenstore-ls -fp | grep scoutapi-dev
/vm/8b7714b8-eeb0-2120-cee7-59273be76f79/name = "scoutapi-dev"   (n0)
/local/domain/0/backend/vbd/12/51715/domain = "scoutapi-dev"   (n0,r12)
/local/domain/0/backend/vbd/12/51715/params = 
"/dev/r5VG/scoutapi-dev-srv"   (n0,r12)
/local/domain/0/backend/vbd/12/51714/domain = "scoutapi-dev"   (n0,r12)
/local/domain/0/backend/vbd/12/51714/params = 
"/dev/r5VG/scoutapi-dev-root"   (n0,r12)
/local/domain/0/backend/vbd/12/51713/domain = "scoutapi-dev"   (n0,r12)
/local/domain/0/backend/vbd/12/51713/params = 
"/dev/r5VG/scoutapi-dev-swap"   (n0,r12)
/local/domain/0/backend/vif/12/0/domain = "scoutapi-dev"   (n0,r12)
/local/domain/0/backend/console/12/0/domain = "scoutapi-dev"   (n0,r12)
/local/domain/12/name = "scoutapi-dev"   (n0,r12)


# DomU scoutapi-dev initially has assigned 256MB
root@on05:~# xm list|grep scoutapi-dev
scoutapi-dev                      12   256     1     -b----      8.8

# ...and it can see that amount
root@scoutapi-dev:~# free -m|grep -B 1 "Mem"
       total       used       free     shared    buffers     cached
Mem:     252         70        182          0          4         38
root@scoutapi-dev:~# cat /proc/meminfo |grep MemTotal
MemTotal:         258908 kB
root@scoutapi-dev:~# cat 
/sys/devices/system/xen_memory/xen_memory0/target_kb
262144


# I increase scoutapi-dev's memory on Dom0
root@on05:~# xm mem-set scoutapi-dev 512
root@on05:~# xm list|grep scoutapi-dev
scoutapi-dev                      12   512     1     -b----      9.0

# DomU seems to be aware of the change (target_kb) but does not use it
root@scoutapi-dev:~# free -m|grep -B 1 "Mem"
         total       used       free     shared    buffers     cached
Mem:       252         70        182          0          4         38
root@scoutapi-dev:~# cat /proc/meminfo |grep MemTotal
MemTotal:         258908 kB
root@scoutapi-dev:~# cat 
/sys/devices/system/xen_memory/xen_memory0/target_kb
262144


# Now I reduce scoutapi-dev's memory
root@on05:~# xm mem-set scoutapi-dev 128
root@on05:~# xm list|grep scoutapi-dev
scoutapi-dev                        12   128     1     -b----      9.1

# DomU can see the change as expected
root@scoutapi-dev:~# free -m|grep -B 1 "Mem"
         total       used       free     shared    buffers     cached
Mem:       128         70         58          0          4         38
root@scoutapi-dev:~# cat /proc/meminfo |grep MemTotal
MemTotal:         131676 kB
root@scoutapi-dev:~# cat 
/sys/devices/system/xen_memory/xen_memory0/target_kb
131072

# Finally, I increase DomU memory to it's original size:
root@on05:~# xm mem-set scoutapi-dev 256
root@on05:~# xm list|grep scoutapi-dev
scoutapi-dev                        12   256     1     -b----      9.2

# DomU can see the increase fine, it seems to have problem
# only if it the new size is bigger than the original.
root@scoutapi-dev:~# free -m|grep -B 1 "Mem"
         total       used       free     shared    buffers     cached
Mem:       252         70        182          0          4         38
root@scoutapi-dev:~# cat /proc/meminfo |grep MemTotal
MemTotal:         258908 kB
root@scoutapi-dev:~# cat 
/sys/devices/system/xen_memory/xen_memory0/target_kb
262144


# This is my config.
# It has been created by xen-tools, but i use a custom
# xen-tools.con and xm.tmpl
root@on05:~# cat /etc/xen/scout-dev.cfg
#
# Configuration file for the Xen instance scout-dev, created
# by xen-tools 4.2 on Tue Nov 13 19:02:28 2012.

name        = 'scout-dev'
memory      = '256'
maxmem      = '8192'
vcpus       = '1'

kernel      = '/boot/vmlinuz-2.6.32-5-xen-amd64'
ramdisk     = '/boot/initrd.img-2.6.32-5-xen-amd64'

root        = '/dev/xvda2 ro'
disk        = [
                  'phy:/dev/r5VG/scout-dev-srv,xvda3,w',
                  'phy:/dev/r5VG/scout-dev-root,xvda2,w',
                  'phy:/dev/r5VG/scout-dev-swap,xvda1,w',
              ]
vif         = [
                'ip=11.22.33.44,mac=00:16:3E:72:7B:5A,bridge=xenbr55',
              ]
on_poweroff = 'destroy'
on_reboot   = 'restart'
on_crash    = 'restart'

root@on05:~# dpkg -la|grep xen|awk '{print $1"\t "$2"\t"$3}'
ii       libxenstore3.0 4.0.1-5.4
ii       linux-image-2.6.32-5-xen-amd64 2.6.32-46
ii       xen-hypervisor-4.0-amd64       4.0.1-5.4
ii       xen-linux-system-2.6.32-5-xen-amd64    2.6.32-46
ii       xen-qemu-dm-4.0        4.0.1-2+squeeze2
ii       xen-tools      4.2-1
ii       xen-utils-4.0  4.0.1-5.4
ii       xen-utils-common       4.0.0-1
ii       xenstore-utils 4.0.1-5.4
ii       xenwatch       0.5.4-2
root@on05:~# uname -a
Linux on05 2.6.32-5-xen-amd64 #1 SMP Sun Sep 23 13:49:30 UTC 2012 x86_64 
GNU/Linux

If you can bring some light on it, that would be just wonderful.

Greetings.

--
Alexandre Kouznetsov


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