RE: FW: [Xen-users] Memory management questions

["Satoshi Uchida" <s-uchida@xxxxxxxxxxxxx>]

Hi.

> I have to do a `xm mem-max` before setting the amount of memory with
`xm mem-set'.

Yes. 
mem-max is braking for increasing memory, but  is not decrease for
allocated memory.
If amount of memory when mem-max is smaller than allocated memory,
I seem to that system outputs error messages by other causes
(ex.netfront).


> Right after it's up, `cat /proc/meminfo` in dom2 shows a MemTotal of
775108k as expected

Really?
In my environments, MemTotal is shown correctly.
(But, LowMemoryTotal is not correctly.)


>  I thought that the balloon driver only allocates/frees memory but
doesn't actually do memory hot(un)plugging?

I seem it too.
In my understanding,
 First, balloon driver create list of available memory address from
memory or mem attributes in extra.
 Then, by communication HyperVisor, available memory within list
allocated into inactive list in OS or
 securing memory from allocated one is freed.
 Therefore, it is delicate that this mechanism called hot plug.

In my guess,

 1. If extra mem attributes in each domains is not all RAM size,
     by repeating to use balloon function,
     actual memory has free aria, but one domain can not use.
     (by hard limit, allocation of memory is overborne.)

 2. If you add physical memory modules,
     you must reboot xen environments.

In this The joy would be cut.


Thanks,
Satoshi UCHIDA

-----Original Message-----
From: Michael Heyse [mailto:mhk@xxxxxxxxxxxxxxxxx] 
Sent: Saturday, January 14, 2006 3:23 AM
To: Satoshi Uchida
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: FW: [Xen-users] Memory management questions

Satoshi Uchida wrote:
> When domain is initialized (started up), memory attribute secure 
> needed memory and memmax attribute is setup restriction and extra mem 
> attribute arranges balloon memory.
> However, first restriction decide memory and memmax attributes, and 
> balloon secure by memory attributes, so mem-max reflects correctly.
> It is nearly to memory attributes.
> After domain waked up, new restriction changes by xm mem-max command.
> 
> So, memory information in xm list is not correctly, but show your 
> request.

OK, thanks. If I understood correctly, I have to do a `xm mem-max`
before setting the amount of memory with `xm mem-set'. But now something
really strange happens. I booted dom2 as described before (with
memory=256 and extra="mem=768M"). Right after it's up, `cat
/proc/meminfo` in dom2 shows a MemTotal of 775108k as expected. Now I do
a `xm mem-max 2 512M`, and `xm top` correctly shows this, `xm list`
still shows the 256M. So now I do a `xm mem-set 2 512M`. Now `xm list`
shows that the domain has 512M available. But `xm top` shows, that dom1
is using only 262116k with a MEMMAX of 524288k. And the strangest thing
is: `cat /proc/meminfo` in dom2 now shows a MemTotal of only 262136k, so
the virtual machine believes that its available memory has shrunk to
256M from 768M. I thought that the balloon driver only allocates/frees
memory but doesn't actually do memory hot(un)plugging?

Could you please explain this to me?

Thanks,
Michael


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