linux-kernel - Re: [BUG] Xen-ballooned memory never returned to domain after partial-free

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Date:   Thu, 12 Dec 2019 15:21:14 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Nicholas Tsirakis <niko.tsirakis@...il.com>,
        boris.ostrovsky@...cle.com
Cc:     xen-devel <xen-devel@...ts.xenproject.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [BUG] Xen-ballooned memory never returned to domain after
 partial-free

On 12.12.19 15:10, Nicholas Tsirakis wrote:
>> And I think this is the problem. We want here:
>>
>>      balloon_stats.target_pages = balloon_stats.current_pages +
>>                                   balloon_stats.target_unpopulated;
> 
> Ahh I knew I was missing something. Tested the patch, works great! "Reported by"
> is fine with me.

Thanks.

> 
> Do you happen to know the answer to my second question? It's not as important,
> but it does confuse me as I wouldn't expect the total memory to be
> balloon-able at
> all with the hotplugging configs disabled.

Ballooning != hotplugging memory

With memory hotplug you can add (or - in theory - remove) memory to the
kernel it didn't know about before.

With ballooning you just give some memory back to the hypervisor, but
kernel still has some knowledge about it (e.g. keeps struct page for
each ballooned memory page).

HTH, Juergen