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clinuxmemorymmap

Can we allocate physically contiguous memory by mmap()?

I need physically contiguous memory in aarch64 Linux 4.15 for an experimental purpose.

I guessed if the required size is smaller than the page size, the allocated memory may be physically contiguous as below.

void * p = mmap(0, getpagesize() - 1, PROT_READ | PROT_WRITE, MAP_SHARED, 0, 0);

After the allocation, I will identify its physical address by /proc/self/pagemap.

However I cannot find any documentation about this. Can I allocate physicall contiguous memory?

Thank you.

Solution

  • You have very little control over physical memory locations. Within a page, the memory will be contiguous (it's more or less the definition of a page). But different pages that are contiguous in virtual address space need not be contiguous in the physical address space (and pages that are contiguous in the physical address space need not be contiguous in the virtual address space).

    Unless you are going to be working in the lowest levels of the kernel memory management, you're not going to be able to spot physical contiguity in a hurry.

    If the memory is dual-ported between Linux and something else, then you may have issues, but simply using mmap() won't resolve them.