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Date:   Wed, 16 Dec 2020 15:40:53 +0100
From:   Oscar Salvador <osalvador@...e.de>
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,
        mhocko@...e.com, song.bao.hua@...ilicon.com, david@...hat.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 v9 08/11] mm/hugetlb: Add a kernel parameter
 hugetlb_free_vmemmap

On Sun, Dec 13, 2020 at 11:45:31PM +0800, Muchun Song wrote:
> Add a kernel parameter hugetlb_free_vmemmap to disable the feature of
> freeing unused vmemmap pages associated with each hugetlb page on boot.
I guess this should read "to enable the feature"?
AFAICS, it is disabled by default.

> Signed-off-by: Muchun Song <songmuchun@...edance.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

> ---
>  Documentation/admin-guide/kernel-parameters.txt |  9 +++++++++
>  Documentation/admin-guide/mm/hugetlbpage.rst    |  3 +++
>  arch/x86/mm/init_64.c                           |  8 ++++++--
>  include/linux/hugetlb.h                         | 19 +++++++++++++++++++
>  mm/hugetlb_vmemmap.c                            | 16 ++++++++++++++++
>  5 files changed, 53 insertions(+), 2 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..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..1bce5f20e6ca 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() ||
> +	    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 ebca2ef02212..7f47f0eeca3b 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -770,6 +770,20 @@ 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 {};
>  
> @@ -923,6 +937,11 @@ 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 02201c2e3dfa..64ad929cac61 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -180,6 +180,22 @@
>  #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)
> +{
> +	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 long free_vmemmap_pages_size_per_hpage(struct hstate *h)
>  {
>  	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
> -- 
> 2.11.0
> 

-- 
Oscar Salvador
SUSE L3

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