Xen dom0 reports incorrect amount of RAM with dom0_mem set
- by xen_amnesiac
I've done a fair bit of searching about this, but have found nothing that answers my question.
I have a system with 6GB of RAM which acts as a Xen server. For reference, it runs Ubuntu 12.04. I've set the kernel parameter dom0_mem:512M,max:512M in /etc/default/grub as follows:
GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=min:512M,max:512M"
I've tried variations of that, with the same result.
My question is this:
With the above set, the dom0 reports in all applications a RAM amount of 422M.
cat /proc/meminfo gives the following:
$ cat /proc/meminfo
MemTotal: 432472 kB
MemFree: 54144 kB
Buffers: 17640 kB
Cached: 220104 kB
SwapCached: 30172 kB
Active: 136500 kB
Inactive: 167780 kB
Active(anon): 6156 kB
Inactive(anon): 60516 kB
Active(file): 130344 kB
Inactive(file): 107264 kB
Unevictable: 52 kB
Mlocked: 52 kB
SwapTotal: 1794044 kB
SwapFree: 1682012 kB
Dirty: 0 kB
Writeback: 0 kB
AnonPages: 39572 kB
Mapped: 8048 kB
Shmem: 136 kB
Slab: 44324 kB
SReclaimable: 22012 kB
SUnreclaim: 22312 kB
KernelStack: 1280 kB
PageTables: 3840 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 2010280 kB
Committed_AS: 329192 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 313988 kB
VmallocChunk: 34359417340 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 524696 kB
DirectMap2M: 0 kB
top, htop, free -m, and byobu's RAM monitor all report the same amount.
At first I thought this was because of the onboard graphics borrowing some memory, but have now switched to a dedicated GPU and it persists.
Is this normal behavior, or has something gone amiss? It's just about 100MB of RAM that's "gone", and I have no idea where it went. I understand that it's normal that not all RAM is available for allocation, but does the system really take an amount relatively high to the amount of RAM available?
