Re: [Xen-devel] [BUG] Xen live migration dom0 memory

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-07-07 at 17:26 +0200, Epiontis IT wrote:
> Hello,
> 
> I already posted on the xen-users list and Ian told me to post a bug 
> report here. We have the following problem:
> 
> When I start a migration with "xl migrate <vm> <destination>" the 
> destination machine sets up a vm "<vm>--incoming" and seems to sync 
> memory because "xl list" shows "Mem" for the incoming vm going up 
> stepwise until 2048. After that though the vm doesn't get launched. The 
> vm is frozen for about a minute, the dom0 begins swapping out the 2GB to 
> disk (because it only has 512M available for itself) and a process

I spoke with Ian Jackson about this this afternoon and we spent some
staring at the pmap, and we are now both very perplexed...

So I've just tried to repro this.

I installed latest 4.5-testing and a 512M dom0 (which as it happens is also
what our automated test system uses). I then migrated a 3GB domU with "xl
migrate <dom> localhost" and it completed successfully. I had to do
localhost migrate due to only having one box, but I don't think this should
matter.
 
I observed the save helper with pmap and never saw any large allocations.

This matches the behaviour that both Ian and I expected.

Your logs show you are running 4.5.1-rc1. I've looked over
git log 4.5.1-rc1..origin/staging-4.5 -- tools/libx[cl]/
and I don't see anything like a fix for a leak etc.

Next step is to revert my test box from staging-4.5 to 4.5.1-rc1 and see
what changes.

Ian.

> 
> /usr/lib/xen-4.5/bin/libxl-save-helper --restore-domain
> 
> takes about 90% of the dom0 memory. After that the vm ist launched, 
> memory consumption goes back to normal, swap space is freed.
> 
> I attached several log and output files in xen_bug_report.txt. In 
> particular Ian wanted to see the pmap of the save helper process which 
> you can find at the end of the file taken during several phases of the 
> migration process.
> 
> 
> Thank you,
> Alex
> 
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