Re: [External] Re: [PATCH v9 05/11] mm/hugetlb: Allocate the vmemmap pages associated with each HugeTLB page

[Muchun Song <songmuchun@bytedance.com>]

On Thu, Dec 17, 2020 at 9:17 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 12/13/20 7:45 AM, Muchun Song wrote:
> > When we free a HugeTLB page to the buddy allocator, we should allocate the
> > vmemmap pages associated with it. We can do that in the __free_hugepage()
> > before freeing it to buddy.
>
> ...
>
> > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> > index 78c527617e8d..ffcf092c92ed 100644
> > --- a/mm/sparse-vmemmap.c
> > +++ b/mm/sparse-vmemmap.c
> > @@ -29,6 +29,7 @@
> >  #include <linux/sched.h>
> >  #include <linux/pgtable.h>
> >  #include <linux/bootmem_info.h>
> > +#include <linux/delay.h>
> >
> >  #include <asm/dma.h>
> >  #include <asm/pgalloc.h>
> > @@ -39,7 +40,8 @@
> >   *
> >   * @rmap_pte:                called for each non-empty PTE (lowest-level) entry.
> >   * @reuse:           the page which is reused for the tail vmemmap pages.
> > - * @vmemmap_pages:   the list head of the vmemmap pages that can be freed.
> > + * @vmemmap_pages:   the list head of the vmemmap pages that can be freed
> > + *                   or is mapped from.
> >   */
> >  struct vmemmap_rmap_walk {
> >       void (*rmap_pte)(pte_t *pte, unsigned long addr,
> > @@ -54,6 +56,9 @@ struct vmemmap_rmap_walk {
> >   */
> >  #define VMEMMAP_TAIL_PAGE_REUSE              -1
> >
> > +/* The gfp mask of allocating vmemmap page */
> > +#define GFP_VMEMMAP_PAGE     (GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN)
> > +
> >  static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
> >                             unsigned long end, struct vmemmap_rmap_walk *walk)
> >  {
> > @@ -200,6 +205,68 @@ void vmemmap_remap_reuse(unsigned long start, unsigned long size)
> >       free_vmemmap_page_list(&vmemmap_pages);
> >  }
> >
> > +static void vmemmap_remap_restore_pte(pte_t *pte, unsigned long addr,
> > +                                   struct vmemmap_rmap_walk *walk)
> > +{
> > +     pgprot_t pgprot = PAGE_KERNEL;
> > +     struct page *page;
> > +     void *to;
> > +
> > +     BUG_ON(pte_page(*pte) != walk->reuse);
> > +
> > +     page = list_first_entry(walk->vmemmap_pages, struct page, lru);
> > +     list_del(&page->lru);
> > +     to = page_to_virt(page);
> > +     copy_page(to, page_to_virt(walk->reuse));
> > +
> > +     set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
> > +}
> > +
> > +static void alloc_vmemmap_page_list(struct list_head *list,
> > +                                 unsigned long nr_pages)
> > +{
> > +     while (nr_pages--) {
> > +             struct page *page;
> > +
> > +retry:
> > +             page = alloc_page(GFP_VMEMMAP_PAGE);
>
> Should we try (or require) the vmemmap page be on the same node as the
> pages they describe?  I imagine performance would be impacted if a
> struct page and the page it describes are on different numa nodes.

Yeah, it is a good idea. I also think that we should do this. I will do that in
the next version. Thanks.

>
> > +             if (unlikely(!page)) {
> > +                     msleep(100);
> > +                     /*
> > +                      * We should retry infinitely, because we cannot
> > +                      * handle allocation failures. Once we allocate
> > +                      * vmemmap pages successfully, then we can free
> > +                      * a HugeTLB page.
> > +                      */
> > +                     goto retry;
> > +             }
> > +             list_add_tail(&page->lru, list);
> > +     }
> > +}
> > +
>
> --
> Mike Kravetz



-- 
Yours,
Muchun