[Xen-devel] Fwd: How does domU memory allocation work?

[Marco Guazzone <marco.guazzone@xxxxxxxxx>]

Hello,

This is somewhat a cross-post. Sorry for this.
I've already posted this question to xen-users:
   http://lists.xenproject.org/archives/html/xen-users/2014-11/msg00087.html
but the only help I've obtained is to look at this graph:
   
http://xenbits.xen.org/hg/staging/xen-unstable.hg/file/default/docs/misc/libxl_memory.txt

Unfortunately, I'm not able to interpret very well this graph as my
knowledge about Xen internals is very minimal.

So, as my last hope, I've decided to repost the message in this ML.
Can someone help me or, at least, point me to a doc written in human
language so as I can understand Xen memory allocation?

Thank you very much for your time

Cheers,

---------- Forwarded message ----------
From: Marco Guazzone <marco.guazzone@xxxxxxxxx>
Date: Fri, Nov 21, 2014 at 5:16 PM
Subject: How does domU memory allocation work?
To: xen-users@xxxxxxxxxxxxx


Hi,

I don't understand how Xen memory allocation works.

Suppose you create a HVM domU with:

maxmem = 3072
memory = 3072

Now, if I quey Xen I gen
* xl list:
    Name  ID   Mem VCPUs    State    Time(s)
    testvm   1  3067     1     -b----      12.8
* xenstore-ls:
    static-max = "3145728"
    target = "3137536"
     videoram = "8192"
*  xl top:
     MEM(k) MEM(%)  MAXMEM(k) MAXMEM(%)
     3141600        3.1         3146752              3.1

So, for the max memory, we have:

CFG_MAXMEM == XENSTORE_STATIC_MAX  <  XL_TOP_MAXMEM

While, for the current memory, we have:

XENSTORE_TARGET < XL_TOP_MEM < CFG_MEMORY < XL_LIST_MEM

I'm really confused.

Could you explain how it works?

Thank you very much.

Best,

-- Marco

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