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    SubjectRe: [PATCH 14/16] mm/thp: add THP allocation helper
    Date
    On 19 Jun 2020, at 17:56, Ralph Campbell wrote:

    > Transparent huge page allocation policy is controlled by several sysfs
    > variables. Rather than expose these to each device driver that needs to
    > allocate THPs, provide a helper function.
    >
    > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
    > ---
    > include/linux/gfp.h | 10 ++++++++++
    > mm/huge_memory.c | 16 ++++++++++++++++
    > 2 files changed, 26 insertions(+)
    >
    > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
    > index 67a0774e080b..1c7d968a27d3 100644
    > --- a/include/linux/gfp.h
    > +++ b/include/linux/gfp.h
    > @@ -562,6 +562,16 @@ extern struct page *alloc_pages_vma(gfp_t gfp_mask, int order,
    > alloc_pages_vma(gfp_mask, 0, vma, addr, numa_node_id(), false)
    > #define alloc_page_vma_node(gfp_mask, vma, addr, node) \
    > alloc_pages_vma(gfp_mask, 0, vma, addr, node, false)
    > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
    > +extern struct page *alloc_transhugepage(struct vm_area_struct *vma,
    > + unsigned long addr);
    > +#else
    > +static inline struct page *alloc_transhugepage(struct vm_area_struct *vma,
    > + unsigned long addr)
    > +{
    > + return NULL;
    > +}
    > +#endif
    >
    > extern unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order);
    > extern unsigned long get_zeroed_page(gfp_t gfp_mask);
    > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    > index 25d95f7b1e98..f749633ed350 100644
    > --- a/mm/huge_memory.c
    > +++ b/mm/huge_memory.c
    > @@ -775,6 +775,22 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
    > return __do_huge_pmd_anonymous_page(vmf, page, gfp);
    > }
    >
    > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
    > +struct page *alloc_transhugepage(struct vm_area_struct *vma,
    > + unsigned long haddr)
    > +{
    > + gfp_t gfp;
    > + struct page *page;
    > +
    > + gfp = alloc_hugepage_direct_gfpmask(vma);
    > + page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
    > + if (page)
    > + prep_transhuge_page(page);
    > + return page;
    > +}
    > +EXPORT_SYMBOL_GPL(alloc_transhugepage);
    > +#endif
    > +
    > static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
    > pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write,
    > pgtable_t pgtable)
    > --
    > 2.20.1

    Why use CONFIG_ARCH_ENABLE_THP_MIGRATION to guard THP allocator helper?
    Shouldn’t CONFIG_TRANSPARENT_HUGEPAGE be used? Also the helper still allocates
    a THP even if transparent_hugepage_enabled(vma) is false, which is wrong, right?


    --
    Best Regards,
    Yan Zi
    [unhandled content-type:application/pgp-signature]
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