mad Engineer
2014-May-18 09:03 UTC
PV Memory allocated difference in kernel 2.6.18 and 3.2
Hi,
This is an old question i asked in serverfault but no one could answer
it properly.
Can someone explain to me why there is memory difference in Guests with
the same configuration?
- *Hypervisor*: Xen 4.2
- *VM1*: Centos 5.7 with 2.6.18-274.el5xen
Assigned memory from Xen is exactly the same as memory inside guest,
524288k (512m):
free -k
total used free shared buffers cached
Mem: 524288 445004 79284 0 18040 182652
-/+ buffers/cache: 244312 279976
Swap: 524280 0 524280
despite showing:
" Memory: 500984k/524288k available (2533k kernel code, 23212k
reserved, 1746k data, 196k init) "
dmesg: http://pastebin.com/FmVRniLJ
*Question1:*
Why does free show exact memory, while dmesg clearly shows 2.5MB for kernel
code and 23MB as reserved?
- *VM2:* Ubuntu 12.04 ,3.2.0-48-
For the same resources Ubuntu 12.04 with pvopskernel is showing 501236k.
free -k
total used free shared buffers cached
Mem: 501236 147188 354048 0 12588 87668
-/+ buffers/cache: 46932 454304
Swap: 0 0 0
dmesg: http://pastebin.com/jgNfcxc5
Memory: 481820k/524288k available (6553k kernel code, 448k absent,
42020k reserved, 6642k data, 924k init)
*Question2:*
What might be the reason for this behavior, can this has anything to do
with with pvops kernel or is it because of changes in Linux 3.0+ Memory
Management?
No memory wastage was one of the reason i liked and promoted PV guests now
i wish i could explain the reason to others.
Thanks
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