physically contiguous pages with mmap

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Hi,

- is there a way to acquire physically contiguous DRAM pages by memory
mapping /dev/mem or /dev/zero?  Would this method guarantee physical
continuity and fail otherwise or just be best-effort and allocate
non-contiguous memory in case of a failure? Any details/insights on
the mmap() flags needed to be used would be welcome.

-  on a similar note. Let's assume the kernel is booted with the
"mem=X" option, where the amount of physical DRAM present in the
system is actually more than X. If a userspace program tries to mmap a
portion of /dev/mem/ beyond the X MBytes visible to the system, what
happens in the kernel? How are the requested "out-of-range" pages
treated differently than normal memory pages? Would this scenario,
i.e. mmaping "out-of-range" pages, be suitable for the first question
above?

thanks for any help,

- Vasilis

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