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Message-ID: <20201120082358.GH3200@dhcp22.suse.cz>
Date: Fri, 20 Nov 2020 09:23:58 +0100
From: Michal Hocko <mhocko@...e.com>
To: Muchun Song <songmuchun@...edance.com>
Cc: corbet@....net, mike.kravetz@...cle.com, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
paulmck@...nel.org, mchehab+huawei@...nel.org,
pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
almasrymina@...gle.com, rientjes@...gle.com, willy@...radead.org,
osalvador@...e.de, song.bao.hua@...ilicon.com,
duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 18/21] mm/hugetlb: Merge pte to huge pmd only for
gigantic page
On Fri 20-11-20 14:43:22, Muchun Song wrote:
> Merge pte to huge pmd if it has ever been split. Now only support
> gigantic page which's vmemmap pages size is an integer multiple of
> PMD_SIZE. This is the simplest case to handle.
I think it would be benefitial for anybody who plan to implement this
for normal PMDs to document challenges while you still have them fresh
in your mind.
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
> arch/x86/include/asm/hugetlb.h | 8 +++
> mm/hugetlb_vmemmap.c | 118 ++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 124 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
> index c601fe042832..1de1c519a84a 100644
> --- a/arch/x86/include/asm/hugetlb.h
> +++ b/arch/x86/include/asm/hugetlb.h
> @@ -12,6 +12,14 @@ static inline bool vmemmap_pmd_huge(pmd_t *pmd)
> {
> return pmd_large(*pmd);
> }
> +
> +#define vmemmap_pmd_mkhuge vmemmap_pmd_mkhuge
> +static inline pmd_t vmemmap_pmd_mkhuge(struct page *page)
> +{
> + pte_t entry = pfn_pte(page_to_pfn(page), PAGE_KERNEL_LARGE);
> +
> + return __pmd(pte_val(entry));
> +}
> #endif
>
> #define hugepages_supported() boot_cpu_has(X86_FEATURE_PSE)
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index c958699d1393..bf2b6b3e75af 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -144,6 +144,14 @@ static inline bool vmemmap_pmd_huge(pmd_t *pmd)
> }
> #endif
>
> +#ifndef vmemmap_pmd_mkhuge
> +#define vmemmap_pmd_mkhuge vmemmap_pmd_mkhuge
> +static inline pmd_t vmemmap_pmd_mkhuge(struct page *page)
> +{
> + return pmd_mkhuge(mk_pmd(page, PAGE_KERNEL));
> +}
> +#endif
> +
> static bool hugetlb_free_vmemmap_disabled __initdata;
>
> static int __init early_hugetlb_free_vmemmap_param(char *buf)
> @@ -422,6 +430,104 @@ static void __remap_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep,
> }
> }
>
> +static void __replace_huge_page_pte_vmemmap(pte_t *ptep, unsigned long start,
> + unsigned int nr, struct page *huge,
> + struct list_head *free_pages)
> +{
> + unsigned long addr;
> + unsigned long end = start + (nr << PAGE_SHIFT);
> + pgprot_t pgprot = PAGE_KERNEL;
> +
> + for (addr = start; addr < end; addr += PAGE_SIZE, ptep++) {
> + struct page *page;
> + pte_t old = *ptep;
> + pte_t entry;
> +
> + prepare_vmemmap_page(huge);
> +
> + entry = mk_pte(huge++, pgprot);
> + VM_WARN_ON(!pte_present(old));
> + page = pte_page(old);
> + list_add(&page->lru, free_pages);
> +
> + set_pte_at(&init_mm, addr, ptep, entry);
> + }
> +}
> +
> +static void replace_huge_page_pmd_vmemmap(pmd_t *pmd, unsigned long start,
> + struct page *huge,
> + struct list_head *free_pages)
> +{
> + unsigned long end = start + VMEMMAP_HPAGE_SIZE;
> +
> + flush_cache_vunmap(start, end);
> + __replace_huge_page_pte_vmemmap(pte_offset_kernel(pmd, start), start,
> + VMEMMAP_HPAGE_NR, huge, free_pages);
> + flush_tlb_kernel_range(start, end);
> +}
> +
> +static pte_t *merge_vmemmap_pte(pmd_t *pmdp, unsigned long addr)
> +{
> + pte_t *pte;
> + struct page *page;
> +
> + pte = pte_offset_kernel(pmdp, addr);
> + page = pte_page(*pte);
> + set_pmd(pmdp, vmemmap_pmd_mkhuge(page));
> +
> + return pte;
> +}
> +
> +static void merge_huge_page_pmd_vmemmap(pmd_t *pmd, unsigned long start,
> + struct page *huge,
> + struct list_head *free_pages)
> +{
> + replace_huge_page_pmd_vmemmap(pmd, start, huge, free_pages);
> + pte_free_kernel(&init_mm, merge_vmemmap_pte(pmd, start));
> + flush_tlb_kernel_range(start, start + VMEMMAP_HPAGE_SIZE);
> +}
> +
> +static inline void dissolve_compound_page(struct page *page, unsigned int order)
> +{
> + int i;
> + unsigned int nr_pages = 1 << order;
> +
> + for (i = 1; i < nr_pages; i++)
> + set_page_count(page + i, 1);
> +}
> +
> +static void merge_gigantic_page_vmemmap(struct hstate *h, struct page *head,
> + pmd_t *pmd)
> +{
> + LIST_HEAD(free_pages);
> + unsigned long addr = (unsigned long)head;
> + unsigned long end = addr + vmemmap_pages_size_per_hpage(h);
> +
> + for (; addr < end; addr += VMEMMAP_HPAGE_SIZE) {
> + void *to;
> + struct page *page;
> +
> + page = alloc_pages(GFP_VMEMMAP_PAGE & ~__GFP_NOFAIL,
> + VMEMMAP_HPAGE_ORDER);
> + if (!page)
> + goto out;
> +
> + dissolve_compound_page(page, VMEMMAP_HPAGE_ORDER);
> + to = page_to_virt(page);
> + memcpy(to, (void *)addr, VMEMMAP_HPAGE_SIZE);
> +
> + /*
> + * Make sure that any data that writes to the
> + * @to is made visible to the physical page.
> + */
> + flush_kernel_vmap_range(to, VMEMMAP_HPAGE_SIZE);
> +
> + merge_huge_page_pmd_vmemmap(pmd++, addr, page, &free_pages);
> + }
> +out:
> + free_vmemmap_page_list(&free_pages);
> +}
> +
> static inline void alloc_vmemmap_pages(struct hstate *h, struct list_head *list)
> {
> int i;
> @@ -454,10 +560,18 @@ void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
> __remap_huge_page_pte_vmemmap);
> if (!freed_vmemmap_hpage_dec(pmd_page(*pmd)) && pmd_split(pmd)) {
> /*
> - * Todo:
> - * Merge pte to huge pmd if it has ever been split.
> + * Merge pte to huge pmd if it has ever been split. Now only
> + * support gigantic page which's vmemmap pages size is an
> + * integer multiple of PMD_SIZE. This is the simplest case
> + * to handle.
> */
> clear_pmd_split(pmd);
> +
> + if (IS_ALIGNED(vmemmap_pages_per_hpage(h), VMEMMAP_HPAGE_NR)) {
> + spin_unlock(ptl);
> + merge_gigantic_page_vmemmap(h, head, pmd);
> + return;
> + }
> }
> spin_unlock(ptl);
> }
> --
> 2.11.0
--
Michal Hocko
SUSE Labs
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