mm: hugetlb: Copy huge_pmd_share from x86 to mm.
Under x86, multiple puds can be made to reference the same bank of huge pmds provided that they represent a full PUD_SIZE of shared huge memory that is aligned to a PUD_SIZE boundary. The code to share pmds does not require any architecture specific knowledge other than the fact that pmds can be indexed, thus can be beneficial to some other architectures. This patch copies the huge pmd sharing (and unsharing) logic from x86/ to mm/ and introduces a new config option to activate it: CONFIG_ARCH_WANTS_HUGE_PMD_SHARE Signed-off-by: Steve Capper <firstname.lastname@example.org> Acked-by: Catalin Marinas <email@example.com> Acked-by: Andrew Morton <firstname.lastname@example.org>
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