Re: [PATCH 3/7] xen/p2m: put reference for superpage

[Julien Grall <julien@xxxxxxx>]

Hi Luca,

On 23/04/2024 09:25, Luca Fancellu wrote:
> From: Penny Zheng <Penny.Zheng@xxxxxxx>
>
> We are doing foreign memory mapping for static shared memory, and
> there is a great possibility that it could be super mapped.
Is this because we are mapping more than one page at the time? Can you 
point me to the code?
> But today, p2m_put_l3_page could not handle superpages.
This was done on purpose. Xen is not preemptible and therefore we need 
to be cautious how much work is done within the p2m code.
With the below proposal, for 1GB mapping, we may end up to call 
put_page() up to 512 * 512 = 262144 times. put_page() can free memory. 
This could be a very long operation.
Have you benchmark how long it would take?

Cheers,

--
Julien Grall