Hi all, can be a stupid question, but there is a method to calculate the free memory in a system that counts also the memory reserved for the Dom0? I tried using xm info and free comand but there is something wrong. A simple example, host with 4 GB, kernel 2.6.32.39, xen 4.0.2, scientific linux 6: -------------------------------------------- xm info total_memory : 4094 free_memory : 1046 free -m total used free shared buffers cached 3456 1090 2365 0 8 127 So from "xm info" i have 3048 MB reserved, but 3456 are for dom0 ( difference -408) ------------------------------------------ Now a system with 16GB, xen 4.1, centos 5: xm info: total_memory : 16381 free_memory : 13633 free -m total used free shared buffers cached 3072 2196 875 0 160 338 For xm info i have 2748 MB reserved, but 3072 are for dom0 (diff -324) If I set the dom0 memory but the difference between xm info data and free remain constant. ------------------------------------------ I have thought of memory reserved for the hypervisor, but then I tried with this configuration: host with 8GB, kernel 2.6.32.39, xen 4.0.2, scientific linux 6: xm info total_memory : 8190 free_memory : 5006 free -m total used free shared buffers cached 3072 2454 617 0 194 338 For xm info i have 3190 MB reserved, but 3072 are for dom0 (diff +112). ------------------------------------------ Someone can explain what happens? There is a simple and reliable way to get as much ram I have available for domU? Thanks, Muriel _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
I don''t have Xen4 and therefore I was not able to reproduce your
numbers, however with a little bit of thinking and a quick check on the manpages
from "free" and "xm" you can understand what happens:
FREE(1) Linux User’s Manual FREE(1)
NAME
free - Display amount of free and used memory in the system
Clearly "free" will only show you the memory from dom0 -- it will not
show you the entire memory of you hardware. "free" doesn''t
even know if it''s running on dom0 or domU. It''s just a legacy
tool that shows memory information from the OS (not from a hypervisor).
If "free" shows you you have "3456MB" total,
"1090MB" used and "2365MB" free on dom0, that means
that''s the amount of memory dom0 has access to -- forget about domU at
that point.
Whenever you launch a new domU, some memory from dom0 will be freed and
allocated to the newly created domU (if you have "ballooning" enabled,
which seems to be your case).
"xm info" on the other hand, is the tool used by Xen to provide
information on how much memory has been allocated to dom0 and existing domUs,
and how much memory is in fact available for new domU guests. From the manpage
from "xm":
free_memory
Available memory (in MB) not allocated to Xen, or any other
Domains.
You should read about memory ballooning and the reasons why you better not use
it:
http://wiki.xensource.com/xenwiki/XenBestPractices
Best regards,
Eduardo Bragatto
On Aug 10, 2011, at 11:33 AM, Muriel wrote:
> Hi all,
> can be a stupid question, but there is a method to calculate the free
> memory in a system that counts also the memory reserved for the Dom0?
> I tried using xm info and free comand but there is something wrong.
> A simple example, host with 4 GB, kernel 2.6.32.39, xen 4.0.2,
> scientific linux 6:
>
> --------------------------------------------
> xm info
> total_memory : 4094
> free_memory : 1046
>
> free -m
> total used free shared buffers cached
> 3456 1090 2365 0 8 127
>
> So from "xm info" i have 3048 MB reserved, but 3456 are for dom0
(
> difference -408)
> ------------------------------------------
>
> Now a system with 16GB, xen 4.1, centos 5:
> xm info:
> total_memory : 16381
> free_memory : 13633
>
> free -m
> total used free shared buffers cached
> 3072 2196 875 0 160 338
>
> For xm info i have 2748 MB reserved, but 3072 are for dom0 (diff -324)
> If I set the dom0 memory but the difference between xm info data and
> free remain constant.
> ------------------------------------------
>
> I have thought of memory reserved for the hypervisor, but then I tried
> with this configuration:
> host with 8GB, kernel 2.6.32.39, xen 4.0.2, scientific linux 6:
> xm info
> total_memory : 8190
> free_memory : 5006
>
> free -m
> total used free shared buffers cached
> 3072 2454 617 0 194 338
>
> For xm info i have 3190 MB reserved, but 3072 are for dom0 (diff +112).
> ------------------------------------------
>
> Someone can explain what happens?
> There is a simple and reliable way to get as much ram I have available for
domU?
>
> Thanks,
> Muriel
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
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hi, xm top thanks walter On 10 Aug 2011, at 16:33, Muriel <mucawhite@gmail.com> wrote:> Hi all, > can be a stupid question, but there is a method to calculate the free > memory in a system that counts also the memory reserved for the Dom0? > I tried using xm info and free comand but there is something wrong. > A simple example, host with 4 GB, kernel 2.6.32.39, xen 4.0.2, > scientific linux 6: > > -------------------------------------------- > xm info > total_memory : 4094 > free_memory : 1046 > > free -m > total used free shared buffers cached > 3456 1090 2365 0 8 127 > > So from "xm info" i have 3048 MB reserved, but 3456 are for dom0 ( > difference -408) > ------------------------------------------ > > Now a system with 16GB, xen 4.1, centos 5: > xm info: > total_memory : 16381 > free_memory : 13633 > > free -m > total used free shared buffers cached > 3072 2196 875 0 160 338 > > For xm info i have 2748 MB reserved, but 3072 are for dom0 (diff -324) > If I set the dom0 memory but the difference between xm info data and > free remain constant. > ------------------------------------------ > > I have thought of memory reserved for the hypervisor, but then I tried > with this configuration: > host with 8GB, kernel 2.6.32.39, xen 4.0.2, scientific linux 6: > xm info > total_memory : 8190 > free_memory : 5006 > > free -m > total used free shared buffers cached > 3072 2454 617 0 194 338 > > For xm info i have 3190 MB reserved, but 3072 are for dom0 (diff +112). > ------------------------------------------ > > Someone can explain what happens? > There is a simple and reliable way to get as much ram I have available for domU? > > Thanks, > Muriel > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> On Aug 10, 2011, at 11:33 AM, Muriel wrote: > >> Someone can explain what happens?That''s what I answered in my last message.>> There is a simple and reliable way to get as much ram I have available for domU?Forgot to answer this little question: yes, there is, "xm info | grep free" will give exactly how much memory you can use to create new domUs. Regards, Eduardo Bragatto. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Wed, Aug 10, 2011 at 6:36 PM, Eduardo Bragatto <eduardo@bragatto.com> wrote:>> On Aug 10, 2011, at 11:33 AM, Muriel wrote: >> >>> Someone can explain what happens? > > That''s what I answered in my last message. > >>> There is a simple and reliable way to get as much ram I have available for domU? > > Forgot to answer this little question: yes, there is, "xm info | grep free" will give exactly how much memory you can use to create new domUs. >Hi Eduardo, thank you for your answer. I am afraid that using free to show the ram allocated for the dom0 has generated a bit of confusion. I know how free works. The problem is that I disabled the balloon in dom0 (but doesn''t boot with a fixed ram) but in my examples i have: free_memory> total_memory - dom0_memory This does not match with: "free_memory: available memory (in MB) not allocated to Xen, or any other Domains" I must set a fixed amount of ram for see correct values in free_memory? Thanks, Muriel _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users