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    SubjectRe: [External] [PATCH 4/8] hugetlb: create remove_hugetlb_page() to separate functionality
    On Thu, Mar 25, 2021 at 8:29 AM Mike Kravetz <mike.kravetz@oracle.com> 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@oracle.com>

    Reviewed-by: Muchun Song <songmuchun@bytedance.com>

    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
    >

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