Xen devel - May 2013 - XL low memory

On Wed, May 29, 2013 at 1:22 AM, Dominic Russell <GTA_doum@hotmail.com>
wrote:
> Hello,
>
> With xl toolstack, is it possible to declare a low memory parameters, like
> we could with xend in the xend-config.sxp file, with the (dom0-min-mem)
> parameter?
>
> I did try to google this, but could only find information about the
> xend-config file, which xl does not read.
> I have a Dell server, on which I tested that the minimum it can go before
> crashing the kernel is 224mb, but the current minimum set in
> libxl_internal.h is only 128mb!  By the mean time, I changed the constant
> and recompiled 4.2.2.  To have a parameter would be easier :).
Hi,

You can do this with Xen command line parameters, at boot time.
See the first section of the following wiki page for reference:

http://wiki.xen.org/wiki/Xen_Best_Practices

Ben

See the comments in domain_build.c above parse_dom0_mem for details:

http://tinyurl.com/pdtjje9

/*
 * dom0_mem=[min:<min_amt>,][max:<max_amt>,][<amt>]
 *
 * <min_amt>: The minimum amount of memory which should be allocated for
dom0.
 * <max_amt>: The maximum amount of memory which should be allocated for
dom0.
 * <amt>:     The precise amount of memory to allocate for dom0.
 *
 * Notes:
 *  1. <amt> is clamped from below by <min_amt> and from above by
available
 *     memory and <max_amt>
 *  2. <min_amt> is clamped from above by available memory and
<max_amt>
 *  3. <min_amt> is ignored if it is greater than <max_amt>
 *  4. If <amt> is not specified, it is calculated as follows:
 *     "All of memory is allocated to domain 0, minus 1/16th which is
reserved
 *      for uses such as DMA buffers (the reservation is clamped to
128MB)."
 *
 * Each value can be specified as positive or negative:
 *  If +ve: The specified amount is an absolute value.
 *  If -ve: The specified amount is subtracted from total available memory.
 */


min:XXX will not be ballooned lower than specified.

On Wed, May 29, 2013 at 9:58 AM, Dominic Russell <GTA_doum@hotmail.com>
wrote:
> Hello,
>
> My understanding of this parameter, is that it sets the starting amount of
> memory, and the maximum authorized.  The memory could be ballooned down
> anyway!  Is that the case?
> I want to keep the balloon feature for now, because there is only two gigs
> of RAM on this computer...
>
> Thanks,
> Dominic
>
> From: Ben Guthro
> Sent: Wednesday, May 29, 2013 9:00 AM
> To: Dominic Russell
> Cc: xen-devel@lists.xensource.com
> Subject: Re: [Xen-devel] XL low memory
>
> On Wed, May 29, 2013 at 1:22 AM, Dominic Russell
<GTA_doum@hotmail.com>
> wrote:
>> Hello,
>>
>> With xl toolstack, is it possible to declare a low memory parameters,
like
>> we could with xend in the xend-config.sxp file, with the (dom0-min-mem)
>> parameter?
>>
>> I did try to google this, but could only find information about the
>> xend-config file, which xl does not read.
>> I have a Dell server, on which I tested that the minimum it can go
before
>> crashing the kernel is 224mb, but the current minimum set in
>> libxl_internal.h is only 128mb!  By the mean time, I changed the
constant
>> and recompiled 4.2.2.  To have a parameter would be easier :).
>
> Hi,
>
> You can do this with Xen command line parameters, at boot time.
> See the first section of the following wiki page for reference:
>
> http://wiki.xen.org/wiki/Xen_Best_Practices
>
> Ben