Xen 4.0.1 Dom0 draws too much memory by nothing apparent - ooms out when streched under 900 MB

Greetings, I've setup a new ubuntu 10.10 server for xen 4.0.1, though it included kernel compilation (creating PVOPS 2.6.32 kernel) and all the stuff by their guide - (generally include xen and download all packages needed and make world + add sata drivers into kernel).

Now everything is running fine, though I've noticed that dom0 takes in too much memory for nothing - right after dom0 is started - 860 MB is marked as used, even with all caches dropped and only service is SSH and XEND (I can turn even this one off and memory won't free)... and it's apparently not some XEN balloon-memory thing- when I "xm mem-set 0 800" it runs OOM-killer and end in restart ....

meminfo is confusing me at this :

cat /proc/meminfo 
MemTotal:        1229376 kB
MemFree:          345440 kB
Buffers:             412 kB
Cached:             8572 kB
SwapCached:            0 kB
Active:            45304 kB
Inactive:          14112 kB
Active(anon):      38464 kB
Inactive(anon):    12304 kB
Active(file):       6840 kB
Inactive(file):     1808 kB
Unevictable:          20 kB
Mlocked:              20 kB
SwapTotal:             0 kB
SwapFree:              0 kB
Dirty:               948 kB
Writeback:             0 kB
AnonPages:         50508 kB
Mapped:             6600 kB
Shmem:               320 kB
Slab:              15904 kB
SReclaimable:       5236 kB
SUnreclaim:        10668 kB
KernelStack:        1016 kB
PageTables:         1664 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:      614688 kB
Committed_AS:     153440 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      264292 kB
VmallocChunk:   34359473836 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:     8647280 kB
DirectMap2M:           0 kB

last lines stand out in particular: DirectMap4k: 8647280 kB what is this direct map ? Apparently it's size I cannot go under, but neither I can use for userspace... anybody could give me a hint what direct map is ? and how can I make it smaller perhaps if that makes any sense. Machine CPU is AMD Opteron 6168.

Could this be caused by some kernel misconfiguration?

By comparison, other xen servers eat just around 100-200 MB for dom0 and their vital processess. I could always clone xen-3.3 image from them, but I've wanted new xen to benefit from the new smp-impoved blk devices ...