diff options
| -rw-r--r-- | include/linux/hugetlb.h | 6 | ||||
| -rw-r--r-- | include/linux/mm.h | 32 | ||||
| -rw-r--r-- | mm/internal.h | 3 | ||||
| -rw-r--r-- | mm/swap.c | 33 |
4 files changed, 60 insertions, 14 deletions
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 251233c1494..d01cc972a1d 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -31,7 +31,6 @@ struct hugepage_subpool *hugepage_new_subpool(long nr_blocks); void hugepage_put_subpool(struct hugepage_subpool *spool); int PageHuge(struct page *page); -int PageHeadHuge(struct page *page_head); void reset_vma_resv_huge_pages(struct vm_area_struct *vma); int hugetlb_sysctl_handler(struct ctl_table *, int, void __user *, size_t *, loff_t *); @@ -104,11 +103,6 @@ static inline int PageHuge(struct page *page) return 0; } -static inline int PageHeadHuge(struct page *page_head) -{ - return 0; -} - static inline void reset_vma_resv_huge_pages(struct vm_area_struct *vma) { } diff --git a/include/linux/mm.h b/include/linux/mm.h index 9fac6dd69b1..f95c71b7c1f 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -414,15 +414,45 @@ static inline int page_count(struct page *page) return atomic_read(&compound_head(page)->_count); } +#ifdef CONFIG_HUGETLB_PAGE +extern int PageHeadHuge(struct page *page_head); +#else /* CONFIG_HUGETLB_PAGE */ +static inline int PageHeadHuge(struct page *page_head) +{ + return 0; +} +#endif /* CONFIG_HUGETLB_PAGE */ + +static inline bool __compound_tail_refcounted(struct page *page) +{ + return !PageSlab(page) && !PageHeadHuge(page); +} + +/* + * This takes a head page as parameter and tells if the + * tail page reference counting can be skipped. + * + * For this to be safe, PageSlab and PageHeadHuge must remain true on + * any given page where they return true here, until all tail pins + * have been released. + */ +static inline bool compound_tail_refcounted(struct page *page) +{ + VM_BUG_ON(!PageHead(page)); + return __compound_tail_refcounted(page); +} + static inline void get_huge_page_tail(struct page *page) { /* * __split_huge_page_refcount() cannot run * from under us. + * In turn no need of compound_trans_head here. */ VM_BUG_ON(page_mapcount(page) < 0); VM_BUG_ON(atomic_read(&page->_count) != 0); - atomic_inc(&page->_mapcount); + if (compound_tail_refcounted(compound_head(page))) + atomic_inc(&page->_mapcount); } extern bool __get_page_tail(struct page *page); diff --git a/mm/internal.h b/mm/internal.h index 684f7aa9692..a85a3ab1f7e 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -51,7 +51,8 @@ static inline void __get_page_tail_foll(struct page *page, VM_BUG_ON(page_mapcount(page) < 0); if (get_page_head) atomic_inc(&page->first_page->_count); - atomic_inc(&page->_mapcount); + if (compound_tail_refcounted(page->first_page)) + atomic_inc(&page->_mapcount); } /* diff --git a/mm/swap.c b/mm/swap.c index e2757fbb04e..bba4aa5bf68 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -88,8 +88,9 @@ static void put_compound_page(struct page *page) /* * THP can not break up slab pages so avoid taking - * compound_lock(). Slab performs non-atomic bit ops - * on page->flags for better performance. In + * compound_lock() and skip the tail page refcounting + * (in _mapcount) too. Slab performs non-atomic bit + * ops on page->flags for better performance. In * particular slab_unlock() in slub used to be a hot * path. It is still hot on arches that do not support * this_cpu_cmpxchg_double(). @@ -102,7 +103,7 @@ static void put_compound_page(struct page *page) * PageTail clear after smp_rmb() and we'll treat it * as a single page. */ - if (PageSlab(page_head) || PageHeadHuge(page_head)) { + if (!__compound_tail_refcounted(page_head)) { /* * If "page" is a THP tail, we must read the tail page * flags after the head page flags. The @@ -117,10 +118,30 @@ static void put_compound_page(struct page *page) * cannot race here. */ VM_BUG_ON(!PageHead(page_head)); - VM_BUG_ON(page_mapcount(page) <= 0); - atomic_dec(&page->_mapcount); - if (put_page_testzero(page_head)) + VM_BUG_ON(page_mapcount(page) != 0); + if (put_page_testzero(page_head)) { + /* + * If this is the tail of a + * slab compound page, the + * tail pin must not be the + * last reference held on the + * page, because the PG_slab + * cannot be cleared before + * all tail pins (which skips + * the _mapcount tail + * refcounting) have been + * released. For hugetlbfs the + * tail pin may be the last + * reference on the page + * instead, because + * PageHeadHuge will not go + * away until the compound + * page enters the buddy + * allocator. + */ + VM_BUG_ON(PageSlab(page_head)); __put_compound_page(page_head); + } return; } else /* |