Re: [RFC PATCH 1/2] mm: hugetlb: Copy huge_pmd_share from x86 to mm.

[Catalin Marinas <catalin.marinas@arm.com>]

Steve,

On Mon, Apr 29, 2013 at 03:55:55PM +0100, Steve Capper wrote:
> 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.

Just wondering whether more of it could be shared. The following look
pretty close to what you'd write for arm64:

- huge_pte_alloc()
- huge_pte_offset() (there is a pud_large macro on x86 which checks for
  present & huge, we can replace it with just pud_huge in this function
  as it already checks for present)
- follow_huge_pud()
- follow_huge_pmd()

Of course, arch-specific macros like pud_huge, pmd_huge would have to go
in a header file.

-- 
Catalin

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