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    SubjectRe: [PATCH v2 07/19] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page
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    On 10/26/20 7:51 AM, Muchun Song wrote:
    > When we allocate a hugetlb page from the buddy, we should free the
    > unused vmemmap pages associated with it. We can do that in the
    > prep_new_huge_page().
    >
    > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
    > ---
    > arch/x86/include/asm/hugetlb.h | 7 +
    > arch/x86/include/asm/pgtable_64_types.h | 8 +
    > include/linux/hugetlb.h | 7 +
    > mm/hugetlb.c | 190 ++++++++++++++++++++++++
    > 4 files changed, 212 insertions(+)
    >
    > diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
    > index f5e882f999cd..7c3eb60c2198 100644
    > --- a/arch/x86/include/asm/hugetlb.h
    > +++ b/arch/x86/include/asm/hugetlb.h
    > @@ -4,10 +4,17 @@
    >
    > #include <asm/page.h>
    > #include <asm-generic/hugetlb.h>
    > +#include <asm/pgtable.h>
    >
    > #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
    > #define VMEMMAP_HPAGE_SHIFT PMD_SHIFT
    > #define arch_vmemmap_support_huge_mapping() boot_cpu_has(X86_FEATURE_PSE)
    > +
    > +#define vmemmap_pmd_huge vmemmap_pmd_huge
    > +static inline bool vmemmap_pmd_huge(pmd_t *pmd)
    > +{
    > + return pmd_large(*pmd);
    > +}
    > #endif
    >
    > #define hugepages_supported() boot_cpu_has(X86_FEATURE_PSE)
    > diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
    > index 52e5f5f2240d..bedbd2e7d06c 100644
    > --- a/arch/x86/include/asm/pgtable_64_types.h
    > +++ b/arch/x86/include/asm/pgtable_64_types.h
    > @@ -139,6 +139,14 @@ extern unsigned int ptrs_per_p4d;
    > # define VMEMMAP_START __VMEMMAP_BASE_L4
    > #endif /* CONFIG_DYNAMIC_MEMORY_LAYOUT */
    >
    > +/*
    > + * VMEMMAP_SIZE - allows the whole linear region to be covered by
    > + * a struct page array.
    > + */
    > +#define VMEMMAP_SIZE (1UL << (__VIRTUAL_MASK_SHIFT - PAGE_SHIFT - \
    > + 1 + ilog2(sizeof(struct page))))
    > +#define VMEMMAP_END (VMEMMAP_START + VMEMMAP_SIZE)
    > +
    > #define VMALLOC_END (VMALLOC_START + (VMALLOC_SIZE_TB << 40) - 1)
    >
    > #define MODULES_VADDR (__START_KERNEL_map + KERNEL_IMAGE_SIZE)
    > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
    > index ace304a6196c..919f47d77117 100644
    > --- a/include/linux/hugetlb.h
    > +++ b/include/linux/hugetlb.h
    > @@ -601,6 +601,13 @@ static inline bool arch_vmemmap_support_huge_mapping(void)
    > }
    > #endif
    >
    > +#ifndef vmemmap_pmd_huge

    Let's add
    #define vmemmap_pmd_huge vmemmap_pmd_huge
    just in case code gets moved around in header file.

    > +static inline bool vmemmap_pmd_huge(pmd_t *pmd)
    > +{
    > + return pmd_huge(*pmd);
    > +}
    > +#endif
    > +
    > #ifndef VMEMMAP_HPAGE_SHIFT
    > #define VMEMMAP_HPAGE_SHIFT PMD_SHIFT
    > #endif
    > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
    > index d6ae9b6876be..aa012d603e06 100644
    > --- a/mm/hugetlb.c
    > +++ b/mm/hugetlb.c
    > @@ -1293,10 +1293,20 @@ static inline void destroy_compound_gigantic_page(struct page *page,
    > #endif
    >
    > #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
    > +#include <linux/bootmem_info.h>
    > +
    > #define RESERVE_VMEMMAP_NR 2U
    > +#define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT)

    Since RESERVE_VMEMMAP_SIZE is not used here, perhaps it should be added
    in the patch where it is first used.

    >
    > #define page_huge_pte(page) ((page)->pmd_huge_pte)
    >
    > +#define vmemmap_hpage_addr_end(addr, end) \
    > +({ \
    > + unsigned long __boundary; \
    > + __boundary = ((addr) + VMEMMAP_HPAGE_SIZE) & VMEMMAP_HPAGE_MASK;\
    > + (__boundary - 1 < (end) - 1) ? __boundary : (end); \
    > +})
    > +
    > static inline unsigned int nr_free_vmemmap(struct hstate *h)
    > {
    > return h->nr_free_vmemmap_pages;
    > @@ -1416,6 +1426,181 @@ static void __init hugetlb_vmemmap_init(struct hstate *h)
    > pr_info("HugeTLB: can free %d vmemmap pages for %s\n",
    > h->nr_free_vmemmap_pages, h->name);
    > }
    > +
    > +static inline spinlock_t *vmemmap_pmd_lockptr(pmd_t *pmd)
    > +{
    > + static DEFINE_SPINLOCK(pgtable_lock);
    > +
    > + return &pgtable_lock;
    > +}

    This is just a global lock. Correct? And hugetlb specific?

    It should be OK as the page table entries for huegtlb pages will not
    overlap with other entries.

    > +
    > +/*
    > + * Walk a vmemmap address to the pmd it maps.
    > + */
    > +static pmd_t *vmemmap_to_pmd(const void *page)
    > +{
    > + unsigned long addr = (unsigned long)page;
    > + pgd_t *pgd;
    > + p4d_t *p4d;
    > + pud_t *pud;
    > + pmd_t *pmd;
    > +
    > + if (addr < VMEMMAP_START || addr >= VMEMMAP_END)
    > + return NULL;
    > +
    > + pgd = pgd_offset_k(addr);
    > + if (pgd_none(*pgd))
    > + return NULL;
    > + p4d = p4d_offset(pgd, addr);
    > + if (p4d_none(*p4d))
    > + return NULL;
    > + pud = pud_offset(p4d, addr);
    > +
    > + WARN_ON_ONCE(pud_bad(*pud));
    > + if (pud_none(*pud) || pud_bad(*pud))
    > + return NULL;
    > + pmd = pmd_offset(pud, addr);
    > +
    > + return pmd;
    > +}

    That routine is not really hugetlb specific. Perhaps we could move it
    to sparse-vmemmap.c? Or elsewhere?

    --
    Mike Kravetz

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