Hi Julien, > On 7 May 2024, at 14:20, Julien Grall <[email protected]> wrote: > > Hi Luca, > > On 23/04/2024 09:25, Luca Fancellu wrote: >> From: Penny Zheng <[email protected]> >> 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?
So, to be honest this patch was originally in Penny’s serie, my knowledge of this side of the codebase is very limited and so I pushed this one basically untouched. From what I can see in the serie the mappings are made in handle_shared_mem_bank, and map_regions_p2mt is called for one page at the time (allocated through the function allocate_domheap_memory (new function introduced in the serie). So is that the case that this patch is not needed? > >> 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? I did not, since its purpose was unclear to me and was not commented in the last serie from Penny. Cheers, Luca
