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Subject: Re: [PATCH v4] xen/balloon: add late_initcall_sync() for initial
 ballooning done
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        xen-devel@lists.xenproject.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Stefano Stabellini <sstabellini@kernel.org>,
        stable@vger.kernel.org,
        =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= 
        <marmarek@invisiblethingslab.com>
References: <20211102091944.17487-1-jgross@suse.com>
 <f986a7c4-3032-fecd-2e19-4d63a2ee10c7@oracle.com>
 <f8e52acc-2566-1ed0-d2a3-21e2d468fab7@oracle.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <3b1f1771-0a96-1f71-9c9d-9fb1a53a266e@suse.com>
Date:   Thu, 4 Nov 2021 17:21:53 +0100
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From: Juergen Gross <jgross@suse.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 xen-devel@lists.xenproject.org, linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>,
 Stefano Stabellini <sstabellini@kernel.org>, stable@vger.kernel.org,
 =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= <marmarek@invisiblethingslab.com>
Message-ID: <3b1f1771-0a96-1f71-9c9d-9fb1a53a266e@suse.com>
Subject: Re: [PATCH v4] xen/balloon: add late_initcall_sync() for initial
 ballooning done
References: <20211102091944.17487-1-jgross@suse.com>
 <f986a7c4-3032-fecd-2e19-4d63a2ee10c7@oracle.com>
 <f8e52acc-2566-1ed0-d2a3-21e2d468fab7@oracle.com>
In-Reply-To: <f8e52acc-2566-1ed0-d2a3-21e2d468fab7@oracle.com>

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On 04.11.21 16:55, Boris Ostrovsky wrote:
>=20
> On 11/3/21 9:55 PM, Boris Ostrovsky wrote:
>>
>> On 11/2/21 5:19 AM, Juergen Gross wrote:
>>> When running as PVH or HVM guest with actual memory < max memory the
>>> hypervisor is using "populate on demand" in order to allow the guest
>>> to balloon down from its maximum memory size. For this to work
>>> correctly the guest must not touch more memory pages than its target
>>> memory size as otherwise the PoD cache will be exhausted and the gues=
t
>>> is crashed as a result of that.
>>>
>>> In extreme cases ballooning down might not be finished today before
>>> the init process is started, which can consume lots of memory.
>>>
>>> In order to avoid random boot crashes in such cases, add a late init
>>> call to wait for ballooning down having finished for PVH/HVM guests.
>>>
>>> Warn on console if initial ballooning fails, panic() after stalling
>>> for more than 3 minutes per default. Add a module parameter for
>>> changing this timeout.
>>>
>>> Cc: <stable@vger.kernel.org>
>>> Reported-by: Marek Marczykowski-G=C3=B3recki=20
>>> <marmarek@invisiblethingslab.com>
>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>
>>
>>
>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>=20
>=20
> This appears to have noticeable effect on boot time (and boot experienc=
e=20
> in general).
>=20
>=20
> I have
>=20
>=20
>  =C2=A0 memory=3D1024
>  =C2=A0 maxmem=3D8192
>=20
>=20
> And my boot time (on an admittedly slow box) went from 33 to 45 seconds=
=2E=20
> And boot pauses in the middle while it is waiting for ballooning to=20
> complete.
>=20
>=20
> [=C2=A0=C2=A0=C2=A0 5.062714] xen:balloon: Waiting for initial ballooni=
ng down having=20
> finished.
> [=C2=A0=C2=A0=C2=A0 5.449696] random: crng init done
> [=C2=A0=C2=A0 34.613050] xen:balloon: Initial ballooning down finished.=


This shows that before it was just by chance that the PoD cache wasn't
exhausted.

> So at least I think we should consider bumping log level down from info=
=2E

Which level would you prefer? warn?

And if so, would you mind doing this while committing (I have one day
off tomorrow)?


Juergen

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