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Date:   Wed, 16 Dec 2020 23:10:05 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, viro@...iv.linux.org.uk,
        Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org,
        mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com,
        Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com,
        anshuman.khandual@....com, jroedel@...e.de,
        Mina Almasry <almasrymina@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH v9 08/11] mm/hugetlb: Add a kernel
 parameter hugetlb_free_vmemmap

On Thu, Dec 17, 2020 at 12:04:11AM +0800, Muchun Song wrote:
> On Wed, Dec 16, 2020 at 10:40 PM Oscar Salvador <osalvador@...e.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.

It still would be great to have an answer for that.

Thanks


> > >  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

-- 
Oscar Salvador
SUSE L3

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