From: Muchun Song <songmuchun@xxxxxxxxxxxxx> Subject: mm: hugetlb: defer freeing of HugeTLB pages In the subsequent patch, we should allocate the vmemmap pages when freeing a HugeTLB page. But update_and_free_page() can be called under any context, 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_and_free_page() is where the call to allocate vmemmmap pages will be inserted. Link: https://lkml.kernel.org/r/20210510030027.56044-6-songmuchun@xxxxxxxxxxxxx Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Cc: Balbir Singh <bsingharora@xxxxxxxxx> Cc: Barry Song <song.bao.hua@xxxxxxxxxxxxx> Cc: Bodeddula Balasubramaniam <bodeddub@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Chen Huang <chenhuang5@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: HORIGUCHI NAOYA <naoya.horiguchi@xxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Joao Martins <joao.m.martins@xxxxxxxxxx> Cc: Joerg Roedel <jroedel@xxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mina Almasry <almasrymina@xxxxxxxxxx> Cc: Oliver Neukum <oneukum@xxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx> Cc: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 83 +++++++++++++++++++++++++++++++++++++---- mm/hugetlb_vmemmap.c | 12 ----- mm/hugetlb_vmemmap.h | 17 ++++++++ 3 files changed, 93 insertions(+), 19 deletions(-) --- a/mm/hugetlb.c~mm-hugetlb-defer-freeing-of-hugetlb-pages +++ a/mm/hugetlb.c @@ -1376,7 +1376,7 @@ static void remove_hugetlb_page(struct h h->nr_huge_pages_node[nid]--; } -static void update_and_free_page(struct hstate *h, struct page *page) +static void __update_and_free_page(struct hstate *h, struct page *page) { int i; struct page *subpage = page; @@ -1399,12 +1399,79 @@ static void update_and_free_page(struct } } +/* + * As update_and_free_page() can be called under any context, so we cannot + * use GFP_KERNEL to allocate vmemmap pages. However, we can defer the + * actual freeing in a workqueue to prevent from using GFP_ATOMIC to allocate + * the vmemmap pages. + * + * free_hpage_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 free_hpage_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_freelist); + +static void free_hpage_workfn(struct work_struct *work) +{ + struct llist_node *node; + + node = llist_del_all(&hpage_freelist); + + while (node) { + struct page *page; + struct hstate *h; + + page = container_of((struct address_space **)node, + struct page, mapping); + node = node->next; + page->mapping = NULL; + /* + * The VM_BUG_ON_PAGE(!PageHuge(page), page) in page_hstate() + * is going to trigger because a previous call to + * remove_hugetlb_page() will set_compound_page_dtor(page, + * NULL_COMPOUND_DTOR), so do not use page_hstate() directly. + */ + h = size_to_hstate(page_size(page)); + + __update_and_free_page(h, page); + + cond_resched(); + } +} +static DECLARE_WORK(free_hpage_work, free_hpage_workfn); + +static inline void flush_free_hpage_work(struct hstate *h) +{ + if (free_vmemmap_pages_per_hpage(h)) + flush_work(&free_hpage_work); +} + +static void update_and_free_page(struct hstate *h, struct page *page, + bool atomic) +{ + if (!free_vmemmap_pages_per_hpage(h) || !atomic) { + __update_and_free_page(h, page); + return; + } + + /* + * Defer freeing to avoid using GFP_ATOMIC to allocate vmemmap pages. + * + * Only call schedule_work() if hpage_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_freelist)) + schedule_work(&free_hpage_work); +} + static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list) { struct page *page, *t_page; list_for_each_entry_safe(page, t_page, list, lru) { - update_and_free_page(h, page); + update_and_free_page(h, page, false); cond_resched(); } } @@ -1471,12 +1538,12 @@ void free_huge_page(struct page *page) if (HPageTemporary(page)) { remove_hugetlb_page(h, page, false); spin_unlock_irqrestore(&hugetlb_lock, flags); - update_and_free_page(h, page); + update_and_free_page(h, page, true); } else if (h->surplus_huge_pages_node[nid]) { /* remove the page from active list */ remove_hugetlb_page(h, page, true); spin_unlock_irqrestore(&hugetlb_lock, flags); - update_and_free_page(h, page); + update_and_free_page(h, page, true); } else { arch_clear_hugepage_flags(page); enqueue_huge_page(h, page); @@ -1795,7 +1862,7 @@ retry: remove_hugetlb_page(h, head, false); h->max_huge_pages--; spin_unlock_irq(&hugetlb_lock); - update_and_free_page(h, head); + update_and_free_page(h, head, false); return 0; } out: @@ -2411,14 +2478,14 @@ retry: * Pages have been replaced, we can safely free the old one. */ spin_unlock_irq(&hugetlb_lock); - update_and_free_page(h, old_page); + update_and_free_page(h, old_page, false); } return ret; free_new: spin_unlock_irq(&hugetlb_lock); - update_and_free_page(h, new_page); + update_and_free_page(h, new_page, false); return ret; } @@ -2832,6 +2899,7 @@ static int set_max_huge_pages(struct hst * pages in hstate via the proc/sysfs interfaces. */ mutex_lock(&h->resize_lock); + flush_free_hpage_work(h); spin_lock_irq(&hugetlb_lock); /* @@ -2941,6 +3009,7 @@ static int set_max_huge_pages(struct hst /* free the pages after dropping lock */ spin_unlock_irq(&hugetlb_lock); update_and_free_pages_bulk(h, &page_list); + flush_free_hpage_work(h); spin_lock_irq(&hugetlb_lock); while (count < persistent_huge_pages(h)) { --- a/mm/hugetlb_vmemmap.c~mm-hugetlb-defer-freeing-of-hugetlb-pages +++ a/mm/hugetlb_vmemmap.c @@ -180,18 +180,6 @@ #define RESERVE_VMEMMAP_NR 2U #define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT) -/* - * How many vmemmap pages associated with a HugeTLB page that can be freed - * to the buddy allocator. - * - * Todo: Returns zero for now, which means the feature is disabled. We will - * 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 hstate *h) { return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT; --- a/mm/hugetlb_vmemmap.h~mm-hugetlb-defer-freeing-of-hugetlb-pages +++ a/mm/hugetlb_vmemmap.h @@ -12,9 +12,26 @@ #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 freed + * to the buddy allocator. + * + * Todo: Returns zero for now, which means the feature is disabled. We will + * 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 */ _
