Re: [PATCH v2 07/19] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page

[Mike Kravetz]

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@xxxxxxxxxxxxx>
> ---
>  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