Subject: Re: [Xen-devel] [PATCH] xen: release lock occasionally during
 ballooning
To: David Vrabel <david.vrabel@citrix.com>, linux-kernel@vger.kernel.org,
        xen-devel@lists.xensource.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com
References: <1436539354-27850-1-git-send-email-jgross@suse.com>
 <55ACCA5E.9070100@citrix.com>
From: Juergen Gross <jgross@suse.com>
Message-ID: <55ACD19F.3050106@suse.com>
Date: Mon, 20 Jul 2015 12:46:55 +0200
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On 07/20/2015 12:15 PM, David Vrabel wrote:
> On 10/07/15 15:42, Juergen Gross wrote:
>> When dom0 is being ballooned balloon_process() will hold the balloon
>> mutex until it is finished. This will block e.g. creation of new
>> domains as the device backends for the new domain need some
>> autoballooned pages for the ring buffers.
>>
>> Avoid this by releasing the balloon mutex from time to time during
>> ballooning. Add a state variable to indicate one balloon_process()
>> is active to avoid multiple balloon processes fighting for the mutex.
>
> Is this state variable necessary? balloon_process() is a work item so
> there should only be one instance of it running anyway, yes?

Hmm, yes. I've been following the comment above balloon_process()
which suggested the possibility of multiple active instances.

I'll send another version of the patch with an updated comment and
removed state variable.


Juergen

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