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

["Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>]

> -----Original Message-----
> From: Muchun Song [mailto:songmuchun@bytedance.com]
> Sent: Tuesday, December 1, 2020 4:19 AM
> To: corbet@lwn.net; mike.kravetz@oracle.com; tglx@linutronix.de;
> mingo@redhat.com; bp@alien8.de; x86@kernel.org; hpa@zytor.com;
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> willy@infradead.org; osalvador@suse.de; mhocko@suse.com; Song Bao Hua (Barry
> Song) <song.bao.hua@hisilicon.com>
> Cc: duanxiongchun@bytedance.com; linux-doc@vger.kernel.org;
> linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> linux-fsdevel@vger.kernel.org; Muchun Song <songmuchun@bytedance.com>
> 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@bytedance.com>


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

> ---
>  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