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SubjectRe: [PATCH 9/8] hugetlb: add pmd_huge_support() to migrate only pmd-based hugepage
Date
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> writes:

> This patch is motivated by the discussion with Aneesh about "extend
> hugepage migration" patchset.
> http://thread.gmane.org/gmane.linux.kernel.mm/103933/focus=104391
> I'll append this to the patchset in the next post, but before that
> I want this patch to be reviewed (I don't want to repeat posting the
> whole set for just minor changes.)
>
> Any comments?
>
> Thanks,
> Naoya Horiguchi
> ---
> From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Date: Mon, 5 Aug 2013 13:33:02 -0400
> Subject: [PATCH] hugetlb: add pmd_huge_support() to migrate only pmd-based
> hugepage
>
> Currently hugepage migration works well only for pmd-based hugepages,
> because core routines of hugepage migration use pmd specific internal
> functions like huge_pte_offset(). So we should not enable the migration
> of other levels of hugepages until we are ready for it.

I guess huge_pte_offset may not be the right reason because archs do
implement huge_pte_offsets even if they are not pmd-based hugepages

pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
{
/* Only called for hugetlbfs pages, hence can ignore THP */
return find_linux_pte_or_hugepte(mm->pgd, addr, NULL);
}

>
> Some users of hugepage migration (mbind, move_pages, and migrate_pages)
> do page table walk and check pud/pmd_huge() there, so they are safe.
> But the other users (softoffline and memory hotremove) don't do this,
> so they can try to migrate unexpected types of hugepages.
>
> To prevent this, we introduce an architecture dependent check of whether
> hugepage are implemented on a pmd basis or not. It returns 0 if pmd_huge()
> returns always 0, and 1 otherwise.
>

so why not #define pmd_huge_support pmd_huge or use pmd_huge directly ?

> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> ---
> arch/arm/mm/hugetlbpage.c | 5 +++++
> arch/arm64/mm/hugetlbpage.c | 5 +++++
> arch/ia64/mm/hugetlbpage.c | 5 +++++
> arch/metag/mm/hugetlbpage.c | 5 +++++
> arch/mips/mm/hugetlbpage.c | 5 +++++
> arch/powerpc/mm/hugetlbpage.c | 10 ++++++++++
> arch/s390/mm/hugetlbpage.c | 5 +++++
> arch/sh/mm/hugetlbpage.c | 5 +++++
> arch/sparc/mm/hugetlbpage.c | 5 +++++
> arch/tile/mm/hugetlbpage.c | 5 +++++
> arch/x86/mm/hugetlbpage.c | 8 ++++++++
> include/linux/hugetlb.h | 2 ++
> mm/migrate.c | 11 +++++++++++
> 13 files changed, 76 insertions(+)
>
> diff --git a/arch/arm/mm/hugetlbpage.c b/arch/arm/mm/hugetlbpage.c
> index 3d1e4a2..3f3b6a7 100644
> --- a/arch/arm/mm/hugetlbpage.c
> +++ b/arch/arm/mm/hugetlbpage.c
> @@ -99,3 +99,8 @@ int pmd_huge(pmd_t pmd)
> {
> return pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
> }
> +
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}

-aneesh


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