[CentOS-virt] Cannot allocate Memory

[Shaun Reitan]

We are planing on moving to xl but have not done so yet.

Our xend configs are untouched so they should match what they were when 
the xen-* packages were installed.

We force dom0 to 1024MB of memory via grub.

On a couple servers were we've seen this issue we've had 16+ GB of 
memory free and the domU was requesting something small like 2GB.

--
Shaun



------ Original Message ------
From: "George Dunlap" <dunlapg at umich.edu>
To: "Shaun Reitan" <shaun.reitan at ndchost.com>; "Discussion about the 
virtualization on CentOS" <centos-virt at centos.org>
Sent: 6/24/2016 4:28:53 AM
Subject: Re: [CentOS-virt] Cannot allocate Memory

>On Wed, Jun 22, 2016 at 6:45 PM, Shaun Reitan 
><shaun.reitan at ndchost.com> wrote:
>>  Any of you guys ever seen an issue with Xen 4.4 were xm cannot create 
>>a
>>  guest because of what looks like an issue allocating memory even 
>>though xm
>>  info shows like 5x the amount of free memory needed? We are still
>>  unfortunately still using xm... it's on my list, i know..
>>
>>  We've had this happen on a couple hosts now.  Only way to resolve 
>>seams to
>>  be rebooting the host.  I'm going to update the host to latest Xen 
>>4.4 now
>>  hoping this is a old bug.
>
>xend hasn't had much love in years, so it's fairly unlikely that this
>has been fixed.
>
>>  Here's from xen logs
>>
>>  [2016-06-22 09:13:50 1958] DEBUG (XendDomainInfo:105)
>>  XendDomainInfo.create(['vm', ['name', 'xxx'], ['memory', 2048],
>>  ['on_xend_start', 'ignore'], ['on_xend_stop', 'ignore'], ['vcpus', 
>>2],
>>  ['oos', 1], ['image', ['linux', ['kernel', 
>>'/kernels/vmlinux-2.6.18.8-4'],
>>  ['videoram', 4], ['args', 'root=/dev/xvda ro xencons=tty console=tty1 
>>'],
>>  ['tsc_mode', 0], ['nomigrate', 0]]], ['s3_integrity', 1], ['device', 
>>['vbd',
>>  ['uname', 'phy:vg/fs_6818'], ['dev', 'xvda'], ['mode', 'w']]], 
>>['device',
>>  ['vbd', ['uname', 'phy:vg/fs_6819'], ['dev', 'xvdb'], ['mode', 
>>'w']]],
>>  ['device', ['vif', ['rate', '40mb/s'], ['mac', 
>>'FE:FD:48:01:F1:E7']]]])
>>  [2016-06-22 09:13:50 1958] DEBUG (XendDomainInfo:2504)
>>  XendDomainInfo.constructDomain
>>  [2016-06-22 09:13:50 1958] DEBUG (balloon:187) Balloon: 7602632 KiB 
>>free;
>>  need 16384; done.
>>  [2016-06-22 09:13:50 1958] ERROR (XendDomainInfo:2566) (12, 'Cannot 
>>allocate
>>  memory')
>>  Traceback (most recent call last):
>>    File 
>>"/usr/lib64/python2.6/site-packages/xen/xend/XendDomainInfo.py", line
>>  2561, in _constructDomain
>>      target = self.info.target())
>>  Error: (12, 'Cannot allocate memory')
>>  [2016-06-22 09:13:50 1958] ERROR (XendDomainInfo:490) VM start failed
>>  Traceback (most recent call last):
>>    File 
>>"/usr/lib64/python2.6/site-packages/xen/xend/XendDomainInfo.py", line
>>  475, in start
>>      XendTask.log_progress(0, 30, self._constructDomain)
>>    File "/usr/lib64/python2.6/site-packages/xen/xend/XendTask.py", 
>>line 209,
>>  in log_progress
>>      retval = func(*args, **kwds)
>>    File 
>>"/usr/lib64/python2.6/site-packages/xen/xend/XendDomainInfo.py", line
>>  2572, in _constructDomain
>>      raise VmError(failmsg)
>>  VmError: Creating domain failed: name=xxx
>>  [2016-06-22 09:13:50 1958] ERROR (XendDomainInfo:110) Domain 
>>construction
>>  failed
>>  Traceback (most recent call last):
>>    File 
>>"/usr/lib64/python2.6/site-packages/xen/xend/XendDomainInfo.py", line
>>  108, in create
>>      vm.start()
>>    File 
>>"/usr/lib64/python2.6/site-packages/xen/xend/XendDomainInfo.py", line
>>  475, in start
>>      XendTask.log_progress(0, 30, self._constructDomain)
>>    File "/usr/lib64/python2.6/site-packages/xen/xend/XendTask.py", 
>>line 209,
>>  in log_progress
>>      retval = func(*args, **kwds)
>>    File 
>>"/usr/lib64/python2.6/site-packages/xen/xend/XendDomainInfo.py", line
>>  2572, in _constructDomain
>>      raise VmError(failmsg)
>>  VmError: Creating domain failed: name=xxx
>
>If you haven't decided to switch to xl, would you mind reposting this
>question to xen-users?  If you do, please also include the output of
>"xl info" after the failure.
>
>The logs tell us that xend is asking dom0 to free up some memory to
>use to create the guest.  My guess is that there's a slight mismatch
>between how much memory xend things needs to be freed and how much
>memory actually needs freeing.
>
>Thanks,
>  -George