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But update_and_free_page() is be called from a non-task context(and hold hugetlb_lock), we can defer the actual freeing in a workqueue to prevent use GFP_ATOMIC to allocate the vmemmap pages. Signed-off-by: Muchun Song --- mm/hugetlb.c | 94 +++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 85 insertions(+), 9 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index aa012d603e06..a5500c79e2df 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1292,6 +1292,8 @@ static inline void destroy_compound_gigantic_page(struct page *page, unsigned int order) { } #endif +static void __free_hugepage(struct hstate *h, struct page *page); + #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP #include @@ -1601,6 +1603,64 @@ static void free_huge_page_vmemmap(struct hstate *h, struct page *head) free_vmemmap_page_list(&free_pages); } + +/* + * As update_and_free_page() is be called from a non-task context(and hold + * hugetlb_lock), we can defer the actual freeing in a workqueue to prevent + * use GFP_ATOMIC to allocate a lot of vmemmap pages. + * + * update_hpage_vmemmap_workfn() locklessly retrieves the linked list of + * pages to be freed and frees them one-by-one. As the page->mapping pointer + * is going to be cleared in update_hpage_vmemmap_workfn() anyway, it is + * reused as the llist_node structure of a lockless linked list of huge + * pages to be freed. + */ +static LLIST_HEAD(hpage_update_freelist); + +static void update_hpage_vmemmap_workfn(struct work_struct *work) +{ + struct llist_node *node; + struct page *page; + + node = llist_del_all(&hpage_update_freelist); + + while (node) { + page = container_of((struct address_space **)node, + struct page, mapping); + node = node->next; + page->mapping = NULL; + __free_hugepage(page_hstate(page), page); + + cond_resched(); + } +} +static DECLARE_WORK(hpage_update_work, update_hpage_vmemmap_workfn); + +static inline void __update_and_free_page(struct hstate *h, struct page *page) +{ + /* No need to allocate vmemmap pages */ + if (!nr_free_vmemmap(h)) { + __free_hugepage(h, page); + return; + } + + /* + * Defer freeing to avoid using GFP_ATOMIC to allocate vmemmap + * pages. + * + * Only call schedule_work() if hpage_update_freelist is previously + * empty. Otherwise, schedule_work() had been called but the workfn + * hasn't retrieved the list yet. + */ + if (llist_add((struct llist_node *)&page->mapping, + &hpage_update_freelist)) + schedule_work(&hpage_update_work); +} + +static inline void free_gigantic_page_comm(struct hstate *h, struct page *page) +{ + free_gigantic_page(page, huge_page_order(h)); +} #else static inline void hugetlb_vmemmap_init(struct hstate *h) { @@ -1618,17 +1678,39 @@ static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page) static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head) { } + +static inline void __update_and_free_page(struct hstate *h, struct page *page) +{ + __free_hugepage(h, page); +} + +static inline void free_gigantic_page_comm(struct hstate *h, struct page *page) +{ + /* + * Temporarily drop the hugetlb_lock, because + * we might block in free_gigantic_page(). + */ + spin_unlock(&hugetlb_lock); + free_gigantic_page(page, huge_page_order(h)); + spin_lock(&hugetlb_lock); +} #endif static void update_and_free_page(struct hstate *h, struct page *page) { - int i; - if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) return; h->nr_huge_pages--; h->nr_huge_pages_node[page_to_nid(page)]--; + + __update_and_free_page(h, page); +} + +static void __free_hugepage(struct hstate *h, struct page *page) +{ + int i; + for (i = 0; i < pages_per_huge_page(h); i++) { page[i].flags &= ~(1 << PG_locked | 1 << PG_error | 1 << PG_referenced | 1 << PG_dirty | @@ -1640,14 +1722,8 @@ static void update_and_free_page(struct hstate *h, struct page *page) set_compound_page_dtor(page, NULL_COMPOUND_DTOR); set_page_refcounted(page); if (hstate_is_gigantic(h)) { - /* - * Temporarily drop the hugetlb_lock, because - * we might block in free_gigantic_page(). - */ - spin_unlock(&hugetlb_lock); destroy_compound_gigantic_page(page, huge_page_order(h)); - free_gigantic_page(page, huge_page_order(h)); - spin_lock(&hugetlb_lock); + free_gigantic_page_comm(h, page); } else { __free_pages(page, huge_page_order(h)); }