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Re: [PATCH 0/2] xen/mm: limit in-place scrubbing
- To: Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 9 Jan 2026 10:29:20 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 09 Jan 2026 10:29:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 09/01/2026 10:15 am, Jan Beulich wrote:
> On 08.01.2026 18:55, Roger Pau Monne wrote:
>> In XenServer we have seen the watchdog occasionally triggering during
>> domain creation if 1GB pages are scrubbed in-place during physmap
>> population.
> That's pretty extreme - writing to 1Gb of memory can't really take over 5s,
> can it?
Sure it can.
> Is there lock contention involved?
Almost certainly, and it's probably the more relevant aspect in this case.
> Or is this when very many CPUs
> try to do the same in parallel?
The scenario is reboot of a VM when Xapi is doing NUMA placement using
per-node claims.
In this case, even with sufficient scrubbed RAM on other nodes, you need
to take from the node you claimed on which might need scrubbing.
The underlying problem is the need to do a long running operation in a
context where you cannot continue, and cannot (reasonably) fail.
~Andrew
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