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Date:   Tue, 18 May 2021 17:52:25 +0200
From:   Cornelia Huck <cohuck@redhat.com>
To:     Christian Borntraeger <borntraeger@de.ibm.com>
Cc:     Claudio Imbrenda <imbrenda@linux.ibm.com>, kvm@vger.kernel.org,
        frankja@linux.ibm.com, thuth@redhat.com, pasic@linux.ibm.com,
        david@redhat.com, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 00/11] KVM: s390: pv: implement lazy destroy
Message-ID: <20210518175225.32f61744.cohuck@redhat.com>
In-Reply-To: <225fe3ec-f2e9-6c76-97e1-b252fe3326b3@de.ibm.com>
References: <20210517200758.22593-1-imbrenda@linux.ibm.com>
        <20210518170537.58b32ffe.cohuck@redhat.com>
        <20210518173624.13d043e3@ibm-vm>
        <225fe3ec-f2e9-6c76-97e1-b252fe3326b3@de.ibm.com>
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On Tue, 18 May 2021 17:45:18 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 18.05.21 17:36, Claudio Imbrenda wrote:
> > On Tue, 18 May 2021 17:05:37 +0200
> > Cornelia Huck <cohuck@redhat.com> wrote:

> >> Can too many not-yet-cleaned-up pages lead to a (temporary) memory
> >> exhaustion?  
> > 
> > in case of reboot, not much; the pages were in use are still in use
> > after the reboot, and they can be swapped.
> > 
> > in case of a shutdown, yes, because the pages are really taken aside
> > and cleared/destroyed in background. they cannot be swapped. they are
> > freed immediately as they are processed, to try to mitigate memory
> > exhaustion scenarios.
> > 
> > in the end, this patchseries is a tradeoff between speed and memory
> > consumption. the memory needs to be cleared up at some point, and that
> > requires time.
> > 
> > in cases where this might be an issue, I introduced a new KVM flag to
> > disable lazy destroy (patch 10)  
> 
> Maybe we could piggy-back on the OOM-kill notifier and then fall back to
> synchronous freeing for some pages?

Sounds like a good idea. If delayed cleanup is safe, you probably want
to have the fast shutdown behaviour.