From 8f251a3d5ce3bdea73bd045ed35db64f32e0d0d9 Mon Sep 17 00:00:00 2001 From: Mike Kravetz Date: Wed, 24 Feb 2021 12:08:56 -0800 Subject: [PATCH] hugetlb: convert page_huge_active() HPageMigratable flag Use the new hugetlb page specific flag HPageMigratable to replace the page_huge_active interfaces. By it's name, page_huge_active implied that a huge page was on the active list. However, that is not really what code checking the flag wanted to know. It really wanted to determine if the huge page could be migrated. This happens when the page is actually added to the page cache and/or task page table. This is the reasoning behind the name change. The VM_BUG_ON_PAGE() calls in the *_huge_active() interfaces are not really necessary as we KNOW the page is a hugetlb page. Therefore, they are removed. The routine page_huge_active checked for PageHeadHuge before testing the active bit. This is unnecessary in the case where we hold a reference or lock and know it is a hugetlb head page. page_huge_active is also called without holding a reference or lock (scan_movable_pages), and can race with code freeing the page. The extra check in page_huge_active shortened the race window, but did not prevent the race. Offline code calling scan_movable_pages already deals with these races, so removing the check is acceptable. Add comment to racy code. [songmuchun@bytedance.com: remove set_page_huge_active() declaration from include/linux/hugetlb.h] Link: https://lkml.kernel.org/r/CAMZfGtUda+KoAZscU0718TN61cSFwp4zy=y2oZ=+6Z2TAZZwng@mail.gmail.com Link: https://lkml.kernel.org/r/20210122195231.324857-3-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz Reviewed-by: Oscar Salvador Reviewed-by: Muchun Song Reviewed-by: Miaohe Lin Acked-by: Michal Hocko Cc: David Hildenbrand Cc: Matthew Wilcox Cc: Naoya Horiguchi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/hugetlbfs/inode.c | 2 +- include/linux/hugetlb.h | 7 ++++-- include/linux/page-flags.h | 6 ----- mm/hugetlb.c | 45 ++++++++++---------------------------- mm/memory_hotplug.c | 9 +++++++- 5 files changed, 25 insertions(+), 44 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 907f6405e805..5a8ed6bd4f87 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -735,7 +735,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset, mutex_unlock(&hugetlb_fault_mutex_table[hash]); - set_page_huge_active(page); + SetHPageMigratable(page); /* * unlock_page because locked by add_to_page_cache() * put_page() due to reference from alloc_huge_page() diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 249c65e1d8ca..77f2a032fe32 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -480,9 +480,13 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr, * HPG_restore_reserve - Set when a hugetlb page consumes a reservation at * allocation time. Cleared when page is fully instantiated. Free * routine checks flag to restore a reservation on error paths. + * HPG_migratable - Set after a newly allocated page is added to the page + * cache and/or page tables. Indicates the page is a candidate for + * migration. */ enum hugetlb_page_flags { HPG_restore_reserve = 0, + HPG_migratable, __NR_HPAGEFLAGS, }; @@ -525,6 +529,7 @@ static inline void ClearHPage##uname(struct page *page) \ * Create functions associated with hugetlb page flags */ HPAGEFLAG(RestoreReserve, restore_reserve) +HPAGEFLAG(Migratable, migratable) #ifdef CONFIG_HUGETLB_PAGE @@ -838,8 +843,6 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma, } #endif -void set_page_huge_active(struct page *page); - #else /* CONFIG_HUGETLB_PAGE */ struct hstate {}; diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index ec5d0290e0ee..db914477057b 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -592,15 +592,9 @@ static inline void ClearPageCompound(struct page *page) #ifdef CONFIG_HUGETLB_PAGE int PageHuge(struct page *page); int PageHeadHuge(struct page *page); -bool page_huge_active(struct page *page); #else TESTPAGEFLAG_FALSE(Huge) TESTPAGEFLAG_FALSE(HeadHuge) - -static inline bool page_huge_active(struct page *page) -{ - return 0; -} #endif diff --git a/mm/hugetlb.c b/mm/hugetlb.c index f5e85dabb7a3..727c09713627 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1364,30 +1364,6 @@ struct hstate *size_to_hstate(unsigned long size) return NULL; } -/* - * Test to determine whether the hugepage is "active/in-use" (i.e. being linked - * to hstate->hugepage_activelist.) - * - * This function can be called for tail pages, but never returns true for them. - */ -bool page_huge_active(struct page *page) -{ - return PageHeadHuge(page) && PagePrivate(&page[1]); -} - -/* never called for tail page */ -void set_page_huge_active(struct page *page) -{ - VM_BUG_ON_PAGE(!PageHeadHuge(page), page); - SetPagePrivate(&page[1]); -} - -static void clear_page_huge_active(struct page *page) -{ - VM_BUG_ON_PAGE(!PageHeadHuge(page), page); - ClearPagePrivate(&page[1]); -} - /* * Internal hugetlb specific page flag. Do not use outside of the hugetlb * code @@ -1449,7 +1425,7 @@ static void __free_huge_page(struct page *page) } spin_lock(&hugetlb_lock); - clear_page_huge_active(page); + ClearHPageMigratable(page); hugetlb_cgroup_uncharge_page(hstate_index(h), pages_per_huge_page(h), page); hugetlb_cgroup_uncharge_page_rsvd(hstate_index(h), @@ -4218,7 +4194,7 @@ retry_avoidcopy: make_huge_pte(vma, new_page, 1)); page_remove_rmap(old_page, true); hugepage_add_new_anon_rmap(new_page, vma, haddr); - set_page_huge_active(new_page); + SetHPageMigratable(new_page); /* Make the old page be freed below */ new_page = old_page; } @@ -4455,12 +4431,12 @@ retry: spin_unlock(ptl); /* - * Only make newly allocated pages active. Existing pages found - * in the pagecache could be !page_huge_active() if they have been - * isolated for migration. + * Only set HPageMigratable in newly allocated pages. Existing pages + * found in the pagecache may not have HPageMigratableset if they have + * been isolated for migration. */ if (new_page) - set_page_huge_active(page); + SetHPageMigratable(page); unlock_page(page); out: @@ -4771,7 +4747,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, update_mmu_cache(dst_vma, dst_addr, dst_pte); spin_unlock(ptl); - set_page_huge_active(page); + SetHPageMigratable(page); if (vm_shared) unlock_page(page); ret = 0; @@ -5610,12 +5586,13 @@ bool isolate_huge_page(struct page *page, struct list_head *list) bool ret = true; spin_lock(&hugetlb_lock); - if (!PageHeadHuge(page) || !page_huge_active(page) || + if (!PageHeadHuge(page) || + !HPageMigratable(page) || !get_page_unless_zero(page)) { ret = false; goto unlock; } - clear_page_huge_active(page); + ClearHPageMigratable(page); list_move_tail(&page->lru, list); unlock: spin_unlock(&hugetlb_lock); @@ -5625,7 +5602,7 @@ unlock: void putback_active_hugepage(struct page *page) { spin_lock(&hugetlb_lock); - set_page_huge_active(page); + SetHPageMigratable(page); list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist); spin_unlock(&hugetlb_lock); put_page(page); diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index ddcb1cd24c60..abe43c1ae920 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1260,7 +1260,14 @@ static int scan_movable_pages(unsigned long start, unsigned long end, if (!PageHuge(page)) continue; head = compound_head(page); - if (page_huge_active(head)) + /* + * This test is racy as we hold no reference or lock. The + * hugetlb page could have been free'ed and head is no longer + * a hugetlb page before the following check. In such unlikely + * cases false positives and negatives are possible. Calling + * code must deal with these scenarios. + */ + if (HPageMigratable(head)) goto found; skip = compound_nr(head) - (page - head); pfn += skip - 1; -- 2.20.1