diff options
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 2 | ||||
| -rw-r--r-- | include/linux/page-flags.h | 78 | ||||
| -rw-r--r-- | mm/hugetlb_vmemmap.c | 62 | ||||
| -rw-r--r-- | mm/sparse-vmemmap.c | 21 |
4 files changed, 130 insertions, 33 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 7123524a86b8..bc39497f5788 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1625,7 +1625,7 @@ [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP enabled. Allows heavy hugetlb users to free up some more - memory (6 * PAGE_SIZE for each 2MB hugetlb page). + memory (7 * PAGE_SIZE for each 2MB hugetlb page). Format: { on | off (default) } on: enable the feature diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 1c3b6e5c8bfd..111e453f23d2 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -190,13 +190,69 @@ enum pageflags { #ifndef __GENERATING_BOUNDS_H +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP +extern bool hugetlb_free_vmemmap_enabled; + +/* + * If the feature of freeing some vmemmap pages associated with each HugeTLB + * page is enabled, the head vmemmap page frame is reused and all of the tail + * vmemmap addresses map to the head vmemmap page frame (furture details can + * refer to the figure at the head of the mm/hugetlb_vmemmap.c). In other + * words, there are more than one page struct with PG_head associated with each + * HugeTLB page. We __know__ that there is only one head page struct, the tail + * page structs with PG_head are fake head page structs. We need an approach + * to distinguish between those two different types of page structs so that + * compound_head() can return the real head page struct when the parameter is + * the tail page struct but with PG_head. + * + * The page_fixed_fake_head() returns the real head page struct if the @page is + * fake page head, otherwise, returns @page which can either be a true page + * head or tail. + */ +static __always_inline const struct page *page_fixed_fake_head(const struct page *page) +{ + if (!hugetlb_free_vmemmap_enabled) + return page; + + /* + * Only addresses aligned with PAGE_SIZE of struct page may be fake head + * struct page. The alignment check aims to avoid access the fields ( + * e.g. compound_head) of the @page[1]. It can avoid touch a (possibly) + * cold cacheline in some cases. + */ + if (IS_ALIGNED((unsigned long)page, PAGE_SIZE) && + test_bit(PG_head, &page->flags)) { + /* + * We can safely access the field of the @page[1] with PG_head + * because the @page is a compound page composed with at least + * two contiguous pages. + */ + unsigned long head = READ_ONCE(page[1].compound_head); + + if (likely(head & 1)) + return (const struct page *)(head - 1); + } + return page; +} +#else +static inline const struct page *page_fixed_fake_head(const struct page *page) +{ + return page; +} +#endif + +static __always_inline int page_is_fake_head(struct page *page) +{ + return page_fixed_fake_head(page) != page; +} + static inline unsigned long _compound_head(const struct page *page) { unsigned long head = READ_ONCE(page->compound_head); if (unlikely(head & 1)) return head - 1; - return (unsigned long)page; + return (unsigned long)page_fixed_fake_head(page); } #define compound_head(page) ((typeof(page))_compound_head(page)) @@ -231,12 +287,13 @@ static inline unsigned long _compound_head(const struct page *page) static __always_inline int PageTail(struct page *page) { - return READ_ONCE(page->compound_head) & 1; + return READ_ONCE(page->compound_head) & 1 || page_is_fake_head(page); } static __always_inline int PageCompound(struct page *page) { - return test_bit(PG_head, &page->flags) || PageTail(page); + return test_bit(PG_head, &page->flags) || + READ_ONCE(page->compound_head) & 1; } #define PAGE_POISON_PATTERN -1l @@ -695,7 +752,20 @@ static inline bool test_set_page_writeback(struct page *page) return set_page_writeback(page); } -__PAGEFLAG(Head, head, PF_ANY) CLEARPAGEFLAG(Head, head, PF_ANY) +static __always_inline bool folio_test_head(struct folio *folio) +{ + return test_bit(PG_head, folio_flags(folio, FOLIO_PF_ANY)); +} + +static __always_inline int PageHead(struct page *page) +{ + PF_POISONED_CHECK(page); + return test_bit(PG_head, &page->flags) && !page_is_fake_head(page); +} + +__SETPAGEFLAG(Head, head, PF_ANY) +__CLEARPAGEFLAG(Head, head, PF_ANY) +CLEARPAGEFLAG(Head, head, PF_ANY) /** * folio_test_large() - Does this folio contain more than one page? diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c index c540c21e26f5..4977f5a520c2 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -124,9 +124,9 @@ * page of page structs (page 0) associated with the HugeTLB page contains the 4 * page structs necessary to describe the HugeTLB. The only use of the remaining * pages of page structs (page 1 to page 7) is to point to page->compound_head. - * Therefore, we can remap pages 2 to 7 to page 1. Only 2 pages of page structs + * Therefore, we can remap pages 1 to 7 to page 0. Only 1 page of page structs * will be used for each HugeTLB page. This will allow us to free the remaining - * 6 pages to the buddy allocator. + * 7 pages to the buddy allocator. * * Here is how things look after remapping. * @@ -134,30 +134,30 @@ * +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+ * | | | 0 | -------------> | 0 | * | | +-----------+ +-----------+ - * | | | 1 | -------------> | 1 | - * | | +-----------+ +-----------+ - * | | | 2 | ----------------^ ^ ^ ^ ^ ^ - * | | +-----------+ | | | | | - * | | | 3 | ------------------+ | | | | - * | | +-----------+ | | | | - * | | | 4 | --------------------+ | | | - * | PMD | +-----------+ | | | - * | level | | 5 | ----------------------+ | | - * | mapping | +-----------+ | | - * | | | 6 | ------------------------+ | - * | | +-----------+ | - * | | | 7 | --------------------------+ + * | | | 1 | ---------------^ ^ ^ ^ ^ ^ ^ + * | | +-----------+ | | | | | | + * | | | 2 | -----------------+ | | | | | + * | | +-----------+ | | | | | + * | | | 3 | -------------------+ | | | | + * | | +-----------+ | | | | + * | | | 4 | ---------------------+ | | | + * | PMD | +-----------+ | | | + * | level | | 5 | -----------------------+ | | + * | mapping | +-----------+ | | + * | | | 6 | -------------------------+ | + * | | +-----------+ | + * | | | 7 | ---------------------------+ * | | +-----------+ * | | * | | * | | * +-----------+ * - * When a HugeTLB is freed to the buddy system, we should allocate 6 pages for + * When a HugeTLB is freed to the buddy system, we should allocate 7 pages for * vmemmap pages and restore the previous mapping relationship. * * For the HugeTLB page of the pud level mapping. It is similar to the former. - * We also can use this approach to free (PAGE_SIZE - 2) vmemmap pages. + * We also can use this approach to free (PAGE_SIZE - 1) vmemmap pages. * * Apart from the HugeTLB page of the pmd/pud level mapping, some architectures * (e.g. aarch64) provides a contiguous bit in the translation table entries @@ -166,7 +166,13 @@ * * The contiguous bit is used to increase the mapping size at the pmd and pte * (last) level. So this type of HugeTLB page can be optimized only when its - * size of the struct page structs is greater than 2 pages. + * size of the struct page structs is greater than 1 page. + * + * Notice: The head vmemmap page is not freed to the buddy allocator and all + * tail vmemmap pages are mapped to the head vmemmap page frame. So we can see + * more than one struct page struct with PG_head (e.g. 8 per 2 MB HugeTLB page) + * associated with each HugeTLB page. The compound_head() can handle this + * correctly (more details refer to the comment above compound_head()). */ #define pr_fmt(fmt) "HugeTLB: " fmt @@ -175,19 +181,21 @@ /* * There are a lot of struct page structures associated with each HugeTLB page. * For tail pages, the value of compound_head is the same. So we can reuse first - * page of tail page structures. We map the virtual addresses of the remaining - * pages of tail page structures to the first tail page struct, and then free - * these page frames. Therefore, we need to reserve two pages as vmemmap areas. + * page of head page structures. We map the virtual addresses of all the pages + * of tail page structures to the head page struct, and then free these page + * frames. Therefore, we need to reserve one pages as vmemmap areas. */ -#define RESERVE_VMEMMAP_NR 2U +#define RESERVE_VMEMMAP_NR 1U #define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT) -bool hugetlb_free_vmemmap_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON); +bool hugetlb_free_vmemmap_enabled __read_mostly = + IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON); +EXPORT_SYMBOL(hugetlb_free_vmemmap_enabled); static int __init early_hugetlb_free_vmemmap_param(char *buf) { /* We cannot optimize if a "struct page" crosses page boundaries. */ - if ((!is_power_of_2(sizeof(struct page)))) { + if (!is_power_of_2(sizeof(struct page))) { pr_warn("cannot free vmemmap pages because \"struct page\" crosses page boundaries\n"); return 0; } @@ -236,7 +244,6 @@ int alloc_huge_page_vmemmap(struct hstate *h, struct page *head) */ ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse, GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE); - if (!ret) ClearHPageVmemmapOptimized(head); @@ -282,9 +289,8 @@ void __init hugetlb_vmemmap_init(struct hstate *h) vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT; /* - * The head page and the first tail page are not to be freed to buddy - * allocator, the other pages will map to the first tail page, so they - * can be freed. + * The head page is not to be freed to buddy allocator, the other tail + * pages will map to the head page, so they can be freed. * * Could RESERVE_VMEMMAP_NR be greater than @vmemmap_pages? It is true * on some architectures (e.g. aarch64). See Documentation/arm64/ diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c index db6df27c852a..e881f5db7091 100644 --- a/mm/sparse-vmemmap.c +++ b/mm/sparse-vmemmap.c @@ -245,6 +245,26 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr, set_pte_at(&init_mm, addr, pte, entry); } +/* + * How many struct page structs need to be reset. When we reuse the head + * struct page, the special metadata (e.g. page->flags or page->mapping) + * cannot copy to the tail struct page structs. The invalid value will be + * checked in the free_tail_pages_check(). In order to avoid the message + * of "corrupted mapping in tail page". We need to reset at least 3 (one + * head struct page struct and two tail struct page structs) struct page + * structs. + */ +#define NR_RESET_STRUCT_PAGE 3 + +static inline void reset_struct_pages(struct page *start) +{ + int i; + struct page *from = start + NR_RESET_STRUCT_PAGE; + + for (i = 0; i < NR_RESET_STRUCT_PAGE; i++) + memcpy(start + i, from, sizeof(*from)); +} + static void vmemmap_restore_pte(pte_t *pte, unsigned long addr, struct vmemmap_remap_walk *walk) { @@ -258,6 +278,7 @@ static void vmemmap_restore_pte(pte_t *pte, unsigned long addr, list_del(&page->lru); to = page_to_virt(page); copy_page(to, (void *)walk->reuse_addr); + reset_struct_pages(to); set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot)); } |