Re: [External] [PATCH 4/8] hugetlb: create remove_hugetlb_page() to separate functionality

[Muchun Song]

On Thu, Mar 25, 2021 at 8:29 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>
> The new remove_hugetlb_page() routine is designed to remove a hugetlb
> page from hugetlbfs processing.  It will remove the page from the active
> or free list, update global counters and set the compound page
> destructor to NULL so that PageHuge() will return false for the 'page'.
> After this call, the 'page' can be treated as a normal compound page or
> a collection of base size pages.
>
> remove_hugetlb_page is to be called with the hugetlb_lock held.
>
> Creating this routine and separating functionality is in preparation for
> restructuring code to reduce lock hold times.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>

Thanks for your effort on this.

> ---
>  mm/hugetlb.c | 70 +++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 45 insertions(+), 25 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 404b0b1c5258..3938ec086b5c 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1327,6 +1327,46 @@ static inline void destroy_compound_gigantic_page(struct page *page,
>                                                 unsigned int order) { }
>  #endif
>
> +/*
> + * Remove hugetlb page from lists, and update dtor so that page appears
> + * as just a compound page.  A reference is held on the page.
> + * NOTE: hugetlb specific page flags stored in page->private are not
> + *      automatically cleared.  These flags may be used in routines
> + *      which operate on the resulting compound page.
> + *
> + * Must be called with hugetlb lock held.
> + */
> +static void remove_hugetlb_page(struct hstate *h, struct page *page,
> +                                                       bool adjust_surplus)
> +{
> +       int nid = page_to_nid(page);
> +
> +       if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
> +               return;
> +
> +       list_del(&page->lru);
> +
> +       if (HPageFreed(page)) {
> +               h->free_huge_pages--;
> +               h->free_huge_pages_node[nid]--;
> +               ClearHPageFreed(page);
> +       }
> +       if (adjust_surplus) {
> +               h->surplus_huge_pages--;
> +               h->surplus_huge_pages_node[nid]--;
> +       }
> +
> +       VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
> +       VM_BUG_ON_PAGE(hugetlb_cgroup_from_page_rsvd(page), page);
> +
> +       ClearHPageTemporary(page);
> +       set_page_refcounted(page);
> +       set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
> +
> +       h->nr_huge_pages--;
> +       h->nr_huge_pages_node[nid]--;
> +}
> +
>  static void update_and_free_page(struct hstate *h, struct page *page)
>  {
>         int i;
> @@ -1335,8 +1375,6 @@ static void update_and_free_page(struct hstate *h, struct page *page)
>         if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
>                 return;
>
> -       h->nr_huge_pages--;
> -       h->nr_huge_pages_node[page_to_nid(page)]--;
>         for (i = 0; i < pages_per_huge_page(h);
>              i++, subpage = mem_map_next(subpage, page, i)) {
>                 subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
> @@ -1344,10 +1382,6 @@ static void update_and_free_page(struct hstate *h, struct page *page)
>                                 1 << PG_active | 1 << PG_private |
>                                 1 << PG_writeback);
>         }
> -       VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
> -       VM_BUG_ON_PAGE(hugetlb_cgroup_from_page_rsvd(page), page);
> -       set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
> -       set_page_refcounted(page);
>         if (hstate_is_gigantic(h)) {
>                 destroy_compound_gigantic_page(page, huge_page_order(h));
>                 free_gigantic_page(page, huge_page_order(h));
> @@ -1415,15 +1449,12 @@ static void __free_huge_page(struct page *page)
>                 h->resv_huge_pages++;
>
>         if (HPageTemporary(page)) {
> -               list_del(&page->lru);
> -               ClearHPageTemporary(page);
> +               remove_hugetlb_page(h, page, false);
>                 update_and_free_page(h, page);
>         } else if (h->surplus_huge_pages_node[nid]) {
>                 /* remove the page from active list */
> -               list_del(&page->lru);
> +               remove_hugetlb_page(h, page, true);
>                 update_and_free_page(h, page);
> -               h->surplus_huge_pages--;
> -               h->surplus_huge_pages_node[nid]--;
>         } else {
>                 arch_clear_hugepage_flags(page);
>                 enqueue_huge_page(h, page);
> @@ -1708,13 +1739,7 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
>                         struct page *page =
>                                 list_entry(h->hugepage_freelists[node].next,
>                                           struct page, lru);
> -                       list_del(&page->lru);
> -                       h->free_huge_pages--;
> -                       h->free_huge_pages_node[node]--;
> -                       if (acct_surplus) {
> -                               h->surplus_huge_pages--;
> -                               h->surplus_huge_pages_node[node]--;
> -                       }
> +                       remove_hugetlb_page(h, page, acct_surplus);
>                         update_and_free_page(h, page);
>                         ret = 1;
>                         break;
> @@ -1752,7 +1777,6 @@ int dissolve_free_huge_page(struct page *page)
>         if (!page_count(page)) {
>                 struct page *head = compound_head(page);
>                 struct hstate *h = page_hstate(head);
> -               int nid = page_to_nid(head);
>                 if (h->free_huge_pages - h->resv_huge_pages == 0)
>                         goto out;
>
> @@ -1783,9 +1807,7 @@ int dissolve_free_huge_page(struct page *page)
>                         SetPageHWPoison(page);
>                         ClearPageHWPoison(head);
>                 }
> -               list_del(&head->lru);
> -               h->free_huge_pages--;
> -               h->free_huge_pages_node[nid]--;
> +               remove_hugetlb_page(h, page, false);
>                 h->max_huge_pages--;
>                 update_and_free_page(h, head);
>                 rc = 0;
> @@ -2553,10 +2575,8 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
>                                 return;
>                         if (PageHighMem(page))
>                                 continue;
> -                       list_del(&page->lru);
> +                       remove_hugetlb_page(h, page, false);
>                         update_and_free_page(h, page);
> -                       h->free_huge_pages--;
> -                       h->free_huge_pages_node[page_to_nid(page)]--;
>                 }
>         }
>  }
> --
> 2.30.2
>