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,
"Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>
Subject: Re: [PATCH v4] xen/balloon: add late_initcall_sync() for initial ballooning done
Date: Thu, 4 Nov 2021 17:44:56 +0100 [thread overview]
Message-ID: <2f3addff-fbe0-8ef0-6407-e879c0e9827f@suse.com> (raw)
In-Reply-To: <18c12ead-ddf1-9231-7f3b-aafddd349dcf@oracle.com>
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On 04.11.21 17:34, Boris Ostrovsky wrote:
>
> On 11/4/21 12:21 PM, Juergen Gross wrote:
>> On 04.11.21 16:55, Boris Ostrovsky wrote:
>>>
>>> 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 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.
>>>>>
>>>>> 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-Górecki
>>>>> <marmarek@invisiblethingslab.com>
>>>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>>>
>>>>
>>>>
>>>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>>
>>>
>>> This appears to have noticeable effect on boot time (and boot
>>> experience in general).
>>>
>>>
>>> I have
>>>
>>>
>>> memory=1024
>>> maxmem=8192
>>>
>>>
>>> And my boot time (on an admittedly slow box) went from 33 to 45
>>> seconds. And boot pauses in the middle while it is waiting for
>>> ballooning to complete.
>>>
>>>
>>> [ 5.062714] xen:balloon: Waiting for initial ballooning down
>>> having finished.
>>> [ 5.449696] random: crng init done
>>> [ 34.613050] xen:balloon: Initial ballooning down finished.
>>
>> This shows that before it was just by chance that the PoD cache wasn't
>> exhausted.
>
>
> True.
>
>
>>
>>> So at least I think we should consider bumping log level down from info.
>>
>> Which level would you prefer? warn?
>>
>
> Notice? Although that won't make much difference as WARN is the default
> level.
Right. That was my thinking.
> I suppose we can't turn scrubbing off at this point?
I don't think we can be sure a ballooned page wasn't in use before. And
it could contain some data e.g. from the loaded initrd, maybe even put
there by the boot loader. So no, I wouldn't want to do that by default.
We could add another value to the xen_scrub_pages boot parameter, like
xen_scrub_pages=not-at-boot or some such. But this should be another
patch. And it should be documented that initrd or kernel data might
leak.
>> And if so, would you mind doing this while committing (I have one day
>> off tomorrow)?
>
>
> Yes, of course.
Thanks.
Juergen
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next prev parent reply other threads:[~2021-11-04 16:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-02 9:19 [PATCH v4] xen/balloon: add late_initcall_sync() for initial ballooning done Juergen Gross
2021-11-04 1:55 ` Boris Ostrovsky
2021-11-04 15:55 ` Boris Ostrovsky
2021-11-04 16:21 ` Juergen Gross
2021-11-04 16:34 ` Boris Ostrovsky
2021-11-04 16:44 ` Juergen Gross [this message]
2021-11-04 17:05 ` Boris Ostrovsky
2021-11-04 16:23 ` Marek Marczykowski-Górecki
2021-11-05 12:18 ` Boris Ostrovsky
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