Fedora xen - Mar 2006 - Page space questions

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@digitalhermit.com

On Mon, 27 Mar 2006, Kwan Lowe wrote:
> 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.
This idea would work, but the domU that shrinks may still need
to move some data from its memory into its own swap area.

The problem is measuring how much memory each domU really needs.
I''ve got some ideas on that, which I''ll be presenting at this
year''s Ottawa Linux Symposium.  Once I''ve finished writing my
paper I''ll start making some info available...

-- 
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