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To:     =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= 
        <marmarek@invisiblethingslab.com>
Cc:     xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        stable@vger.kernel.org
References: <20211028105952.10011-1-jgross@suse.com>
 <YXsFO2TMRiJTQM2q@mail-itl>
From:   Juergen Gross <jgross@suse.com>
Subject: Re: [PATCH] xen/balloon: add late_initcall_sync() for initial
 ballooning done
Message-ID: <27e7619a-a797-5c46-9f9f-015ab488e31c@suse.com>
Date:   Fri, 29 Oct 2021 06:48:44 +0200
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From: Juergen Gross <jgross@suse.com>
To: =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?=
 <marmarek@invisiblethingslab.com>
Cc: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
 Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 Stefano Stabellini <sstabellini@kernel.org>, stable@vger.kernel.org
Message-ID: <27e7619a-a797-5c46-9f9f-015ab488e31c@suse.com>
Subject: Re: [PATCH] xen/balloon: add late_initcall_sync() for initial
 ballooning done
References: <20211028105952.10011-1-jgross@suse.com>
 <YXsFO2TMRiJTQM2q@mail-itl>
In-Reply-To: <YXsFO2TMRiJTQM2q@mail-itl>

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On 28.10.21 22:16, Marek Marczykowski-G=C3=B3recki wrote:
> On Thu, Oct 28, 2021 at 12:59:52PM +0200, 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 guest=

>> 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.
>>
>> Cc: <stable@vger.kernel.org>
>> Reported-by: Marek Marczykowski-G=C3=B3recki <marmarek@invisiblethings=
lab.com>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>=20
> It may happen that initial balloon down fails (state=3D=3DBP_ECANCELED)=
=2E In
> that case, it waits indefinitely. I think it should rather report a
> failure (and panic? it's similar to OOM before PID 1 starts, so rather
> hard to recover), instead of hanging.

Okay, I can add something like that. I'm thinking of issuing a failure
message in case of credit not having changed for 1 minute and panic()
after two more minutes. Is this fine?


Juergen

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