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But update_and_free_page() is always called with holding hugetlb_lock, so we cannot use GFP_KERNEL to allocate vmemmap pages. However, we can defer the actual freeing in a kworker to prevent from using GFP_ATOMIC to allocate the vmemmap pages. The update_hpage_vmemmap_workfn() is where the call to allocate vmemmmap pages will be inserted. Signed-off-by: Muchun Song Reviewed-by: Mike Kravetz --- mm/hugetlb.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++= ++++-- mm/hugetlb_vmemmap.c | 12 --------- mm/hugetlb_vmemmap.h | 17 ++++++++++++ 3 files changed, 89 insertions(+), 14 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 140135fc8113..c165186ec2cf 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1292,15 +1292,85 @@ static inline void destroy_compound_gigantic_page= (struct page *page, unsigned int order) { } #endif =20 -static void update_and_free_page(struct hstate *h, struct page *page) +static void __free_hugepage(struct hstate *h, struct page *page); + +/* + * As update_and_free_page() is always called with holding hugetlb_lock,= so we + * cannot use GFP_KERNEL to allocate vmemmap pages. However, we can defe= r the + * actual freeing in a workqueue to prevent from using GFP_ATOMIC to all= ocate + * the vmemmap pages. + * + * The update_hpage_vmemmap_workfn() is where the call to allocate vmemm= map + * pages will be inserted. + * + * 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 i= s going + * to be cleared in update_hpage_vmemmap_workfn() anyway, it is reused a= s the + * llist_node structure of a lockless linked list of huge pages to be fr= eed. + */ +static LLIST_HEAD(hpage_update_freelist); + +static void update_hpage_vmemmap_workfn(struct work_struct *work) { - int i; + struct llist_node *node; + + node =3D llist_del_all(&hpage_update_freelist); + + while (node) { + struct page *page; + struct hstate *h; + + page =3D container_of((struct address_space **)node, + struct page, mapping); + node =3D node->next; + page->mapping =3D NULL; + h =3D page_hstate(page); + + spin_lock(&hugetlb_lock); + __free_hugepage(h, page); + spin_unlock(&hugetlb_lock); =20 + 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 (!free_vmemmap_pages_per_hpage(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 void update_and_free_page(struct hstate *h, struct page *page) +{ if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) return; =20 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 =3D 0; i < pages_per_huge_page(h); i++) { page[i].flags &=3D ~(1 << PG_locked | 1 << PG_error | 1 << PG_referenced | 1 << PG_dirty | diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c index 4ffa2a4ae2a8..19f1898aaede 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -178,18 +178,6 @@ #define RESERVE_VMEMMAP_NR 2U #define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT) =20 -/* - * How many vmemmap pages associated with a HugeTLB page that can be fre= ed - * to the buddy allocator. - * - * Todo: Returns zero for now, which means the feature is disabled. We w= ill - * enable it once all the infrastructure is there. - */ -static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h= ) -{ - return 0; -} - static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hst= ate *h) { return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT; diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h index 6923f03534d5..01f8637adbe0 100644 --- a/mm/hugetlb_vmemmap.h +++ b/mm/hugetlb_vmemmap.h @@ -12,9 +12,26 @@ =20 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP void free_huge_page_vmemmap(struct hstate *h, struct page *head); + +/* + * How many vmemmap pages associated with a HugeTLB page that can be fre= ed + * to the buddy allocator. + * + * Todo: Returns zero for now, which means the feature is disabled. We w= ill + * enable it once all the infrastructure is there. + */ +static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h= ) +{ + return 0; +} #else static inline void free_huge_page_vmemmap(struct hstate *h, struct page = *head) { } + +static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h= ) +{ + return 0; +} #endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */ #endif /* _LINUX_HUGETLB_VMEMMAP_H */ --=20 2.11.0