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

From: Oscar Salvador
Date: Wed Dec 16 2020 - 17:11:17 EST

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@xxxxxxx> 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