Re: [Xen-devel] failed to start centos 5 domU with maxmem=30000

[Vasiliy G Tolstov <v.tolstov@xxxxxxxxx>]

Ð ÐÑÐ, 12/08/2010 Ð 11:34 -0700, Jeremy Fitzhardinge ÐÐÑÐÑ:
> On 08/12/2010 05:24 AM, Vasiliy G Tolstov wrote:
> > Ð ÐÑÐ, 12/08/2010 Ð 05:17 -0700, Dan Magenheimer ÐÐÑÐÑ:
> >>> From: Vasiliy G Tolstov [mailto:v.tolstov@xxxxxxxxx]
> >>> Sent: Thursday, August 12, 2010 5:38 AM
> >>> To: Pasi KÃrkkÃinen
> >>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> >>> Subject: Re: [Xen-devel] failed to start centos 5 domU with
> >>> maxmem=30000
> >>>
> >>> Ð ÐÑÐ, 12/08/2010 Ð 14:37 +0300, Pasi KÃrkkÃinen ÐÐÑÐÑ:
> >>>> On Thu, Aug 12, 2010 at 02:24:05PM +0400, Vasiliy G Tolstov wrote:
> >>>>> Hello. I'm try to start centos domU pvm under sles 11 sp1 xen
> >>> kernel
> >>>>> with memory=512 and maxmem=30000. Centos doing boot and freeze.
> >>>>> If i'm try to use maxmem=15000 all works.
> >>>>>
> >>>>> Can You tell me what's wrong?
> >>>>>
> >>>> Is the centos PV domU 32bit or 64bit ?
> >>> 64 bit kernel-xen.
> >>>
> >>> I found this in xen sources:
> >>>
> >>> /* Simple continuous piecewiese linear function:
> >>>           *  max MiB ->  min MiB  gradient
> >>>           *       0         0
> >>>           *      16        16
> >>>           *      32        24
> >>>           *     128        72    (1/2)
> >>>           *     512       168    (1/4)
> >>>           *    2048       360    (1/8)
> >>>           *    8192       552    (1/32)
> >>>           *   32768      1320
> >>>           *  131072      4392
> >>>           */
> >>>
> >>> Why this is not provided in documentation or on web site?
> >> Hi Vasily --
> >>
> >> This function limits how far memory can be reduced when
> >> ballooning a guest (including dom0).  It is only a heuristic
> >> but is intended to take into account the various overheads
> >> a guest Linux kernel requires to manage memory to avoid
> >> out-of-memory conditions.
> >>
> >> But I think you are correct... the same (or similar)
> >> function should be published as it also serves as a
> >> guideline for the ratio between memory= and maxmem=
> >> parameters when creating a guest:  If the ratio
> >> of maxmem divided by memory is too high, the guest
> >> will not even boot.
> >>
> > Is that possible to use memory=32 and maxmem=60000 ?
> 
> A factor of ~2000 between smallest and largest size won't work.  The 
> problem is that lots of kernel structures are scaled with the amount of 
> boot-time memory, and they'll simply be overloaded when you add more 
> memory.  For example, the page structure array for 60GB needs ~15.3 
> million entries, which at 64 bytes per entry will take ~980MB...
> 

Ok. Thank You. Bu can some one provide correct ratio for memory and
maxmemory that others not to make mistakes and not try to post bugs on
that? =)

> >> I am curious as to why you would specify memory= so
> >> much smaller than maxmem=.  Are you trying to overcommit
> >> memory for guests that are often idle but sometimes use
> >> a very large amount of memory?
> > We want to provide ability to use small as possible memory if the guest
> > is idle. And much as possible when the guest under heavy load.
> 
> This is exactly the use-case for the hotplug memory stuff Daniel is 
> working on - which I guess is why you've been testing it.

This is problem, because a'm using centos, debian, ubuntu, opensuse and
other systems in domU, but i read that tmem support needed in dom0 and
domU. Debian and Ubuntu i think, does not support this... But i'm try.


-- 
Vasiliy G Tolstov <v.tolstov@xxxxxxxxx>
Selfip.Ru


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