RE: [PATCH v7 13/15] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap

From: Song Bao Hua (Barry Song)
Date: Thu Dec 03 2020 - 19:03:09 EST



> -----Original Message-----
> From: Muchun Song [mailto:songmuchun@xxxxxxxxxxxxx]
> Sent: Tuesday, December 1, 2020 4:19 AM
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> Song) <song.bao.hua@xxxxxxxxxxxxx>
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> Subject: [PATCH v7 13/15] mm/hugetlb: Add a kernel parameter
> hugetlb_free_vmemmap
>
> Add a kernel parameter hugetlb_free_vmemmap to disable the feature of
> freeing unused vmemmap pages associated with each hugetlb page on boot.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>


Reviewed-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx>

> ---
> Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
> Documentation/admin-guide/mm/hugetlbpage.rst | 3 +++
> arch/x86/mm/init_64.c | 5 +++--
> include/linux/hugetlb.h | 19 +++++++++++++++++++
> mm/hugetlb_vmemmap.c | 18 +++++++++++++++++-
> 5 files changed, 51 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index 3ae25630a223..9e6854f21d55 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1551,6 +1551,15 @@
> 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.
> + 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..6a8b57f6d3b7 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 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 155cb06a6961..fcdc020904a8 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 +1558,7 @@ int __meminit vmemmap_populate(unsigned long start,
> unsigned long end, int node,
> {
> int err;
>
> - if (IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP))
> + if (is_hugetlb_free_vmemmap_enabled())
> err = vmemmap_populate_basepages(start, end, node, NULL);
> else if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> err = vmemmap_populate_basepages(start, end, node, NULL);
> @@ -1613,7 +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) ||
> - IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP)) {
> + is_hugetlb_free_vmemmap_enabled()) {
> 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 4efeccb7192c..66d82ae7b712 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -773,6 +773,20 @@ static inline void huge_ptep_modify_prot_commit(struct
> vm_area_struct *vma,
> }
> #endif
>
> +#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 {};
>
> @@ -926,6 +940,11 @@ 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 a3714db7f400..ebc710d148e4 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -131,6 +131,21 @@ typedef void (*vmemmap_remap_pte_func_t)(struct page
> *reuse, pte_t *pte,
> unsigned long start, unsigned long end,
> void *priv);
>
> +bool hugetlb_free_vmemmap_enabled;
> +
> +static int __init early_hugetlb_free_vmemmap_param(char *buf)
> +{
> + 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);
>
> static inline unsigned int vmemmap_pages_per_hpage(struct hstate *h)
> {
> @@ -325,7 +340,8 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> unsigned int nr_pages = pages_per_huge_page(h);
> unsigned int vmemmap_pages;
>
> - if (!is_power_of_2(sizeof(struct page))) {
> + if (!is_power_of_2(sizeof(struct page)) ||
> + !hugetlb_free_vmemmap_enabled) {
> pr_info("disable freeing vmemmap pages for %s\n", h->name);
> return;
> }
> --
> 2.11.0

Thanks
Barry