[xenpreview-dev] boot ine dom0_mem=memory

[Alexander Vallens]

Same here. Before using dom0-mem we found that adding domUs was usually
OK. At boot time, when launching domUs automatically, it would have no
trouble allocating memory. Starting a domU on an already booted system,
 however, sometimes would not allocate memory properly. Looking at top
reveals that dom0 at boot time would "take" as much memory as possible
for itself and allocating most of it to cache, so we concluded that that
much memory was overkill.

We, therefore, decided to implement dom0-mem=1G, which is still
overkill, but since we're running openSuse 10.2, which employs that
memory hog ZenWorks, we opted to better be safe than sorry. ;-)

My take: perhaps dom0-mem is not necessary, if ballooning in fact works
properly, but we've found the latter to be inconsistent. I recommend
going with dom0-mem, which doesn't set an absolute max for dom0, but
does free up a bunch of memory for domUs.

Hope this helps!
Alexander


Manzer, Kirk wrote:
> I have been using the dom0_mem parameter on the kernel for a while. I
> limit dom0 to either 1 or 2 GB of memory depending on what the server is
> doing, then I have no issues starting and domUs.  Prior to using
> dom0_mem I was constantly having issues with starting domUs.
> 
> 
> Kirk A. Manzer 
> HP
> TSG Solution Alliances, Linux
> Phone: (281)-514-4979 
> Cell: (832)-563-8120 
> Fax: (281)-514-5802 
> kirk.manzer at hp.com 
> 
> 
> -----Original Message-----
> From: xenpreview-dev-bounces at forge.novell.com
> [mailto:xenpreview-dev-bounces at forge.novell.com] On Behalf Of
> Jan.Albrecht at bertelsmann.de
> Sent: Wednesday, May 09, 2007 12:30 PM
> To: jbeulich at novell.com
> Cc: xenpreview-dev at forge.novell.com
> Subject: RE: [xenpreview-dev] boot ine dom0_mem=memory
> 
> My current xmtop output does look like this:
> 
> xentop - 19:26:43   Xen 3.0.4_13138-0.23_x
> 5 domains: 1 running, 4 blocked, 0 paused, 0 crashed, 0 dying, 0
> shutdown
> Mem: 7339416k total, 7337800k used, 1616k free    CPUs: 2 @ 1866MHz
> NAME  STATE   CPU(sec) CPU(%)     MEM(k) MEM(%)  MAXMEM(k) MAXMEM(%)
> VCPUS NETS NETTX(k) NETRX(k) VBDS   VBD_OO   
> 3004 --b---       2522    1.0    1580928   21.5    1605632      21.9
> 1    2        0        0    4        0
> 3005 --b---      24691    1.0     270208    3.7     278528       3.8
> 1    2        0        0    2        0
> 3006 --b---     265829    1.8    1056640   14.4    1064960      14.5
> 1    2        0        0    3        0
> 3007 --b---       8178    1.8    1056640   14.4    1064960      14.5
> 1    2        0        0    3        0
> Domain-0 -----r     181795   11.5    3217408   43.8   no limit       n/a
> 2    4  2168479   840665    0        0
> 
> As you can see I've 7GB for the whole server and 3,75GB for the domUs in
> use. But xm top does only report 1616k free memory.
> I've I do create an another domain on this server:
> Will dom0 free some of it's mem to the new domain? If not the dom0_mem
> parameter would make sense to me.
> 
> Jan
> 
>> -----Original Message-----
>> From: Jan Beulich [mailto:jbeulich at novell.com] 
>> Sent: Wednesday, May 09, 2007 3:10 PM
>> To: Albrecht, Jan, NMI-DC
>> Cc: xenpreview-dev at forge.novell.com
>> Subject: Re: [xenpreview-dev] boot ine dom0_mem=memory
>>
>>> is the line
>>> dom0_mem=<memory size>
>>> still useful?
>>> I mean I've commented out this line and dom0 does take 3.2 GB of RAM,
>>> which limits my domU a bit. If I do limit dom0 to lets say 
>> 256MB, would
>>> that make any difference?
>>  
>> If you want to avoid ballooning failures, the option may be 
>> useful, but as
>> long as your dom0 doesn't really allocate all that memory (so that the
>> balloon driver can't grab it anymore) there should be no 
>> problem omitting
>> it. (256Mb for dom0 would be questionable at least - I'd 
>> certainly not set it
>> to this small a value.)
>>
>> Jan