From: Zi Yan <[email protected]> To split a THP to any lower order (except order-1) pages, we need to reform THPs on subpages at given order and add page refcount based on the new page order. Also we need to reinitialize page_deferred_list after removing the page from the split_queue, otherwise a subsequent split will see list corruption when checking the page_deferred_list again.
It has many uses, like minimizing the number of pages after truncating a huge pagecache page. For anonymous THPs, we can only split them to order-0 like before until we add support for any size anonymous THPs. Order-1 folio is not supported because _deferred_list, which is used by partially mapped folios, is stored in subpage 2 and an order-1 folio only has subpage 0 and 1. Signed-off-by: Zi Yan <[email protected]> --- include/linux/huge_mm.h | 21 +++++--- mm/huge_memory.c | 114 +++++++++++++++++++++++++++++++--------- 2 files changed, 101 insertions(+), 34 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 5adb86af35fc..de0c89105076 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -265,10 +265,11 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr, void folio_prep_large_rmappable(struct folio *folio); bool can_split_folio(struct folio *folio, int *pextra_pins); -int split_huge_page_to_list(struct page *page, struct list_head *list); +int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, + unsigned int new_order); static inline int split_huge_page(struct page *page) { - return split_huge_page_to_list(page, NULL); + return split_huge_page_to_list_to_order(page, NULL, 0); } void deferred_split_folio(struct folio *folio); @@ -422,7 +423,8 @@ can_split_folio(struct folio *folio, int *pextra_pins) return false; } static inline int -split_huge_page_to_list(struct page *page, struct list_head *list) +split_huge_page_to_list_to_order(struct page *page, struct list_head *list, + unsigned int new_order) { return 0; } @@ -519,17 +521,20 @@ static inline bool thp_migration_supported(void) } #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ -static inline int split_folio_to_list(struct folio *folio, - struct list_head *list) +static inline int split_folio_to_list_to_order(struct folio *folio, + struct list_head *list, int new_order) { - return split_huge_page_to_list(&folio->page, list); + return split_huge_page_to_list_to_order(&folio->page, list, new_order); } -static inline int split_folio(struct folio *folio) +static inline int split_folio_to_order(struct folio *folio, int new_order) { - return split_folio_to_list(folio, NULL); + return split_folio_to_list_to_order(folio, NULL, new_order); } +#define split_folio_to_list(f, l) split_folio_to_list_to_order(f, l, 0) +#define split_folio(f) split_folio_to_order(f, 0) + /* * archs that select ARCH_WANTS_THP_SWAP but don't support THP_SWP due to * limitations in the implementation like arm64 MTE can override this to diff --git a/mm/huge_memory.c b/mm/huge_memory.c index ad7133c97428..d0e555a8ea98 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2718,11 +2718,14 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, static void unmap_folio(struct folio *folio) { - enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD | - TTU_SYNC | TTU_BATCH_FLUSH; + enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC | + TTU_BATCH_FLUSH; VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); + if (folio_test_pmd_mappable(folio)) + ttu_flags |= TTU_SPLIT_HUGE_PMD; + /* * Anon pages need migration entries to preserve them, but file * pages can simply be left unmapped, then faulted back on demand. @@ -2756,7 +2759,6 @@ static void lru_add_page_tail(struct page *head, struct page *tail, struct lruvec *lruvec, struct list_head *list) { VM_BUG_ON_PAGE(!PageHead(head), head); - VM_BUG_ON_PAGE(PageCompound(tail), head); VM_BUG_ON_PAGE(PageLRU(tail), head); lockdep_assert_held(&lruvec->lru_lock); @@ -2777,7 +2779,8 @@ static void lru_add_page_tail(struct page *head, struct page *tail, } static void __split_huge_page_tail(struct folio *folio, int tail, - struct lruvec *lruvec, struct list_head *list) + struct lruvec *lruvec, struct list_head *list, + unsigned int new_order) { struct page *head = &folio->page; struct page *page_tail = head + tail; @@ -2847,10 +2850,15 @@ static void __split_huge_page_tail(struct folio *folio, int tail, * which needs correct compound_head(). */ clear_compound_head(page_tail); + if (new_order) { + prep_compound_page(page_tail, new_order); + folio_prep_large_rmappable(page_folio(page_tail)); + } /* Finally unfreeze refcount. Additional reference from page cache. */ - page_ref_unfreeze(page_tail, 1 + (!folio_test_anon(folio) || - folio_test_swapcache(folio))); + page_ref_unfreeze(page_tail, + 1 + ((!folio_test_anon(folio) || folio_test_swapcache(folio)) ? + folio_nr_pages(page_folio(page_tail)) : 0)); if (folio_test_young(folio)) folio_set_young(new_folio); @@ -2868,7 +2876,7 @@ static void __split_huge_page_tail(struct folio *folio, int tail, } static void __split_huge_page(struct page *page, struct list_head *list, - pgoff_t end) + pgoff_t end, unsigned int new_order) { struct folio *folio = page_folio(page); struct page *head = &folio->page; @@ -2877,10 +2885,11 @@ static void __split_huge_page(struct page *page, struct list_head *list, unsigned long offset = 0; unsigned int nr = thp_nr_pages(head); int i, nr_dropped = 0; + unsigned int new_nr = 1 << new_order; int order = folio_order(folio); /* complete memcg works before add pages to LRU */ - split_page_memcg(head, order, 0); + split_page_memcg(head, order, new_order); if (folio_test_anon(folio) && folio_test_swapcache(folio)) { offset = swp_offset(folio->swap); @@ -2893,8 +2902,8 @@ static void __split_huge_page(struct page *page, struct list_head *list, ClearPageHasHWPoisoned(head); - for (i = nr - 1; i >= 1; i--) { - __split_huge_page_tail(folio, i, lruvec, list); + for (i = nr - new_nr; i >= new_nr; i -= new_nr) { + __split_huge_page_tail(folio, i, lruvec, list, new_order); /* Some pages can be beyond EOF: drop them from page cache */ if (head[i].index >= end) { struct folio *tail = page_folio(head + i); @@ -2910,29 +2919,41 @@ static void __split_huge_page(struct page *page, struct list_head *list, __xa_store(&head->mapping->i_pages, head[i].index, head + i, 0); } else if (swap_cache) { + /* + * split anonymous THPs (including swapped out ones) to + * non-zero order not supported + */ + VM_WARN_ONCE(new_order, + "Split swap-cached anon folio to non-0 order not supported"); __xa_store(&swap_cache->i_pages, offset + i, head + i, 0); } } - ClearPageCompound(head); + if (!new_order) + ClearPageCompound(head); + else { + struct folio *new_folio = (struct folio *)head; + + folio_set_order(new_folio, new_order); + } unlock_page_lruvec(lruvec); /* Caller disabled irqs, so they are still disabled here */ - split_page_owner(head, order, 0); + split_page_owner(head, order, new_order); /* See comment in __split_huge_page_tail() */ if (PageAnon(head)) { /* Additional pin to swap cache */ if (PageSwapCache(head)) { - page_ref_add(head, 2); + page_ref_add(head, 1 + new_nr); xa_unlock(&swap_cache->i_pages); } else { page_ref_inc(head); } } else { /* Additional pin to page cache */ - page_ref_add(head, 2); + page_ref_add(head, 1 + new_nr); xa_unlock(&head->mapping->i_pages); } local_irq_enable(); @@ -2944,7 +2965,15 @@ static void __split_huge_page(struct page *page, struct list_head *list, if (folio_test_swapcache(folio)) split_swap_cluster(folio->swap); - for (i = 0; i < nr; i++) { + /* + * set page to its compound_head when split to non order-0 pages, so + * we can skip unlocking it below, since PG_locked is transferred to + * the compound_head of the page and the caller will unlock it. + */ + if (new_order) + page = compound_head(page); + + for (i = 0; i < nr; i += new_nr) { struct page *subpage = head + i; if (subpage == page) continue; @@ -2978,29 +3007,35 @@ bool can_split_folio(struct folio *folio, int *pextra_pins) } /* - * This function splits huge page into normal pages. @page can point to any - * subpage of huge page to split. Split doesn't change the position of @page. + * This function splits huge page into pages in @new_order. @page can point to + * any subpage of huge page to split. Split doesn't change the position of + * @page. + * + * NOTE: order-1 folio is not supported because _deferred_list, which is used + * by partially mapped folios, is stored in subpage 2 and an order-1 folio + * only has subpage 0 and 1. * * Only caller must hold pin on the @page, otherwise split fails with -EBUSY. * The huge page must be locked. * * If @list is null, tail pages will be added to LRU list, otherwise, to @list. * - * Both head page and tail pages will inherit mapping, flags, and so on from - * the hugepage. + * Pages in new_order will inherit mapping, flags, and so on from the hugepage. * - * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if - * they are not mapped. + * GUP pin and PG_locked transferred to @page or the compound page @page belongs + * to. Rest subpages can be freed if they are not mapped. * * Returns 0 if the hugepage is split successfully. * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under * us. */ -int split_huge_page_to_list(struct page *page, struct list_head *list) +int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, + unsigned int new_order) { struct folio *folio = page_folio(page); struct deferred_split *ds_queue = get_deferred_split_queue(folio); - XA_STATE(xas, &folio->mapping->i_pages, folio->index); + /* reset xarray order to new order after split */ + XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order); struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; int extra_pins, ret; @@ -3010,6 +3045,26 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); + /* Cannot split THP to order-1 (no order-1 THPs) */ + if (new_order == 1) { + VM_WARN_ONCE(1, "Cannot split to order-1 folio"); + return -EINVAL; + } + + if (new_order) { + /* Split shmem folio to non-zero order not supported */ + if (shmem_mapping(folio->mapping)) { + VM_WARN_ONCE(1, "Split shmem folio to non-0 order not support"); + return -EINVAL; + } + /* No split if the file system does not support large folio */ + if (!mapping_large_folio_support(folio->mapping)) { + VM_WARN_ONCE(1, "Split file folio to non-0 order not support"); + return -EINVAL; + } + } + + is_hzp = is_huge_zero_page(&folio->page); if (is_hzp) { pr_warn_ratelimited("Called split_huge_page for huge zero page\n"); @@ -3105,14 +3160,21 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) if (folio_ref_freeze(folio, 1 + extra_pins)) { if (!list_empty(&folio->_deferred_list)) { ds_queue->split_queue_len--; - list_del(&folio->_deferred_list); + /* + * Reinitialize page_deferred_list after removing the + * page from the split_queue, otherwise a subsequent + * split will see list corruption when checking the + * page_deferred_list. + */ + list_del_init(&folio->_deferred_list); } spin_unlock(&ds_queue->split_queue_lock); if (mapping) { int nr = folio_nr_pages(folio); xas_split(&xas, folio, folio_order(folio)); - if (folio_test_pmd_mappable(folio)) { + if (folio_test_pmd_mappable(folio) && + new_order < HPAGE_PMD_ORDER) { if (folio_test_swapbacked(folio)) { __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, -nr); @@ -3124,7 +3186,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) } } - __split_huge_page(page, list, end); + __split_huge_page(page, list, end, new_order); ret = 0; } else { spin_unlock(&ds_queue->split_queue_lock); -- 2.43.0
