Re: [External] Re: [PATCH v9 08/11] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap

[Muchun Song <songmuchun@bytedance.com>]

On Wed, Dec 16, 2020 at 10:40 PM Oscar Salvador <osalvador@suse.de> wrote:
>
> 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@bytedance.com>
>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>

Thanks Oscar.

>
> > ---
> >  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



-- 
Yours,
Muchun