Can some one explain me why there is memory difference in Guests with same configuration:
Hypervisor:xen 4.2 64 bit
VM1: Centos 5.7 with 2.6.18-274.el5xen,
Assigned memory from xen is exactly 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
" Memory: 500984k/524288k available (2533k kernel code, 23212k reserved, 1746k data, 196k init) "
here Why free showed exact memory,where dmesg clear showed 2.5mb for kernel code and 23mb as reserved.
VM2: Ubuntu 12.04 ,3.2.0-48-
For 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
Memory: 481820k/524288k available (6553k kernel code, 448k absent, 42020k reserved, 6642k data, 924k init)
What could be the reason for this behavior can this has something to do with with pvops kernel(linux-kernel with xen support) or is it because of any changes in Linux 3.0+ Memory Management.