[Fedora-xen] Page space questions

[Kwan Lowe]

Hello All:
I've been successfully running several domains a test box under various workloads
for about 48 hours now. Domains include an httpd server, mysql database, DNS, and
development domain.

My question is about memory sizing and page space. On a physical box one would
allocate an appropriate page space on the local disks. In the DomainU's, however,
would there be any advantage to maybe disabling page space entirely and allocating a
larger base memory from the host?  Will the Domain0 be able to allocate more
physical memory than is available by using page space?

E.g.
The physical box (1G RAM) currently has four 128-192M domains with 128-256M page
space defined in each DomainU. DomainU's are backed by LVM devices on a single 200G
physical disk. I would like to have four domains of 256M apiece. This is greater
than the available physical RAM, but at any one point the total memory in use by the
DomainUs is much less. I'd probably have to tweak the individual overcommit settings
in each DomainU.

Anyhoo, the rationale is that the Domain0 may be better able to deal with disk I/O
rather than each DomainU hitting the disk...

If this is fatally flawed reasoning, another thought would be to have a monitor
process on each DomainU report back to the Domain0. It would send memory commit
information which the Domain0 could use to mem-set the DomainU's lower or higher.
I'm thinking of a dynamic memory allocation scheme that could better utilize
available physical memory.

Thoughts?  Suggestions? Derision?

(BTW, xen just rocks. It compares very favorably with the VMWare and AIX
micropartitions I use at my day job :D ).

-- 
* The Digital Hermit   http://www.digitalhermit.com
* Unix and Linux Solutions   kwan at digitalhermit.com