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SubjectRe: [PATCH v14 5/8] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
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Date
Hi:
On 2021/2/4 11:50, Muchun Song wrote:
> Add a kernel parameter hugetlb_free_vmemmap to enable the feature of
> freeing unused vmemmap pages associated with each hugetlb page on boot.
>
> We disables PMD mapping of vmemmap pages for x86-64 arch when this
> feature is enabled. Because vmemmap_remap_free() depends on vmemmap
> being base page mapped.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>

Looks good to me. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>

> ---
> Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
> Documentation/admin-guide/mm/hugetlbpage.rst | 3 +++
> arch/x86/mm/init_64.c | 8 ++++++--
> include/linux/hugetlb.h | 19 +++++++++++++++++++
> mm/hugetlb_vmemmap.c | 22 ++++++++++++++++++++++
> 5 files changed, 64 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 5adf1e57e932..7db2591f3ad3 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1577,6 +1577,20 @@
> Documentation/admin-guide/mm/hugetlbpage.rst.
> Format: size[KMG]
>
> + hugetlb_free_vmemmap=
> + [KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,
> + this controls freeing unused vmemmap pages associated
> + with each HugeTLB page. When this option is enabled,
> + we disable PMD/huge page mapping of vmemmap pages which
> + increase page table pages. So if a user/sysadmin only
> + uses a small number of HugeTLB pages (as a percentage
> + of system memory), they could end up using more memory
> + with hugetlb_free_vmemmap on as opposed to off.
> + Format: { on | off (default) }
> +
> + on: enable the feature
> + off: disable the feature
> +
> hung_task_panic=
> [KNL] Should the hung task detector generate panics.
> Format: 0 | 1
> diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
> index f7b1c7462991..3a23c2377acc 100644
> --- a/Documentation/admin-guide/mm/hugetlbpage.rst
> +++ b/Documentation/admin-guide/mm/hugetlbpage.rst
> @@ -145,6 +145,9 @@ default_hugepagesz
>
> will all result in 256 2M huge pages being allocated. Valid default
> huge page size is architecture dependent.
> +hugetlb_free_vmemmap
> + When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables freeing
> + unused vmemmap pages associated with each HugeTLB page.
>
> When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages``
> indicates the current number of pre-allocated huge pages of the default size.
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 0435bee2e172..39f88c5faadc 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -34,6 +34,7 @@
> #include <linux/gfp.h>
> #include <linux/kcore.h>
> #include <linux/bootmem_info.h>
> +#include <linux/hugetlb.h>
>
> #include <asm/processor.h>
> #include <asm/bios_ebda.h>
> @@ -1557,7 +1558,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
> {
> int err;
>
> - if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> + if ((is_hugetlb_free_vmemmap_enabled() && !altmap) ||
> + end - start < PAGES_PER_SECTION * sizeof(struct page))
> err = vmemmap_populate_basepages(start, end, node, NULL);
> else if (boot_cpu_has(X86_FEATURE_PSE))
> err = vmemmap_populate_hugepages(start, end, node, altmap);
> @@ -1585,6 +1587,8 @@ void register_page_bootmem_memmap(unsigned long section_nr,
> pmd_t *pmd;
> unsigned int nr_pmd_pages;
> struct page *page;
> + bool base_mapping = !boot_cpu_has(X86_FEATURE_PSE) ||
> + is_hugetlb_free_vmemmap_enabled();
>
> for (; addr < end; addr = next) {
> pte_t *pte = NULL;
> @@ -1610,7 +1614,7 @@ void register_page_bootmem_memmap(unsigned long section_nr,
> }
> get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO);
>
> - if (!boot_cpu_has(X86_FEATURE_PSE)) {
> + if (base_mapping) {
> next = (addr + PAGE_SIZE) & PAGE_MASK;
> pmd = pmd_offset(pud, addr);
> if (pmd_none(*pmd))
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 37fd248ce271..ad249e56ac49 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -854,6 +854,20 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
>
> void set_page_huge_active(struct page *page);
>
> +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +extern bool hugetlb_free_vmemmap_enabled;
> +
> +static inline bool is_hugetlb_free_vmemmap_enabled(void)
> +{
> + return hugetlb_free_vmemmap_enabled;
> +}
> +#else
> +static inline bool is_hugetlb_free_vmemmap_enabled(void)
> +{
> + return false;
> +}
> +#endif
> +
> #else /* CONFIG_HUGETLB_PAGE */
> struct hstate {};
>
> @@ -1007,6 +1021,11 @@ static inline void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr
> pte_t *ptep, pte_t pte, unsigned long sz)
> {
> }
> +
> +static inline bool is_hugetlb_free_vmemmap_enabled(void)
> +{
> + return false;
> +}
> #endif /* CONFIG_HUGETLB_PAGE */
>
> static inline spinlock_t *huge_pte_lock(struct hstate *h,
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 0bd6b8d7282d..224a3cb69bf9 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -183,6 +183,28 @@
> #define RESERVE_VMEMMAP_NR 2U
> #define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT)
>
> +bool hugetlb_free_vmemmap_enabled;
> +
> +static int __init early_hugetlb_free_vmemmap_param(char *buf)
> +{
> + /* We cannot optimize if a "struct page" crosses page boundaries. */
> + if ((!is_power_of_2(sizeof(struct page)))) {
> + pr_warn("cannot free vmemmap pages because \"struct page\" crosses page boundaries\n");
> + return 0;
> + }
> +
> + if (!buf)
> + return -EINVAL;
> +
> + if (!strcmp(buf, "on"))
> + hugetlb_free_vmemmap_enabled = true;
> + else if (strcmp(buf, "off"))
> + return -EINVAL;
> +
> + return 0;
> +}
> +early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param);
> +
> /*
> * How many vmemmap pages associated with a HugeTLB page that can be freed
> * to the buddy allocator.
>

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