[PATCH v9 5/8] mm/huge_memory: remove the old, unused __split_huge_page()

Zi Yan
2025-02-26T21:00:58Z

Now split_huge_page_to_list_to_order() uses the new backend split code in
__folio_split_without_mapping(), the old __split_huge_page() and
__split_huge_page_tail() can be removed.

Signed-off-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kirill A. Shuemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Kairui Song <kasong@tencent.com>
---
mm/huge_memory.c | 207 -----------------------------------------------
1 file changed, 207 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0e45937c0d91..e7e50b2b23f6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3286,213 +3286,6 @@ static void lru_add_page_tail(struct folio *folio, struct page *tail,
}
}

-static void __split_huge_page_tail(struct folio *folio, int tail,
- struct lruvec *lruvec, struct list_head *list,
- unsigned int new_order)
-{
- struct page *head = &folio->page;
- struct page *page_tail = head + tail;
- /*
- * Careful: new_folio is not a "real" folio before we cleared PageTail.
- * Don't pass it around before clear_compound_head().
- */
- struct folio *new_folio = (struct folio *)page_tail;
-
- VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
-
- /*
- * Clone page flags before unfreezing refcount.
- *
- * After successful get_page_unless_zero() might follow flags change,
- * for example lock_page() which set PG_waiters.
- *
- * Note that for mapped sub-pages of an anonymous THP,
- * PG_anon_exclusive has been cleared in unmap_folio() and is stored in
- * the migration entry instead from where remap_page() will restore it.
- * We can still have PG_anon_exclusive set on effectively unmapped and
- * unreferenced sub-pages of an anonymous THP: we can simply drop
- * PG_anon_exclusive (-> PG_mappedtodisk) for these here.
- */
- page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
- page_tail->flags |= (head->flags &
- ((1L << PG_referenced) |
- (1L << PG_swapbacked) |
- (1L << PG_swapcache) |
- (1L << PG_mlocked) |
- (1L << PG_uptodate) |
- (1L << PG_active) |
- (1L << PG_workingset) |
- (1L << PG_locked) |
- (1L << PG_unevictable) |
-#ifdef CONFIG_ARCH_USES_PG_ARCH_2
- (1L << PG_arch_2) |
-#endif
-#ifdef CONFIG_ARCH_USES_PG_ARCH_3
- (1L << PG_arch_3) |
-#endif
- (1L << PG_dirty) |
- LRU_GEN_MASK | LRU_REFS_MASK));
-
- /* ->mapping in first and second tail page is replaced by other uses */
- VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
- page_tail);
- new_folio->mapping = folio->mapping;
- new_folio->index = folio->index + tail;
-
- /*
- * page->private should not be set in tail pages. Fix up and warn once
- * if private is unexpectedly set.
- */
- if (unlikely(page_tail->private)) {
- VM_WARN_ON_ONCE_PAGE(true, page_tail);
- page_tail->private = 0;
- }
- if (folio_test_swapcache(folio))
- new_folio->swap.val = folio->swap.val + tail;
-
- /* Page flags must be visible before we make the page non-compound. */
- smp_wmb();
-
- /*
- * Clear PageTail before unfreezing page refcount.
- *
- * After successful get_page_unless_zero() might follow put_page()
- * which needs correct compound_head().
- */
- clear_compound_head(page_tail);
- if (new_order) {
- prep_compound_page(page_tail, new_order);
- folio_set_large_rmappable(new_folio);
- }
-
- /* Finally unfreeze refcount. Additional reference from page cache. */
- page_ref_unfreeze(page_tail,
- 1 + ((!folio_test_anon(folio) || folio_test_swapcache(folio)) ?
- folio_nr_pages(new_folio) : 0));
-
- if (folio_test_young(folio))
- folio_set_young(new_folio);
- if (folio_test_idle(folio))
- folio_set_idle(new_folio);
-
- folio_xchg_last_cpupid(new_folio, folio_last_cpupid(folio));
-
- /*
- * always add to the tail because some iterators expect new
- * pages to show after the currently processed elements - e.g.
- * migrate_pages
- */
- lru_add_page_tail(folio, page_tail, lruvec, list);
-}
-
-static void __split_huge_page(struct page *page, struct list_head *list,
- pgoff_t end, unsigned int new_order)
-{
- struct folio *folio = page_folio(page);
- struct page *head = &folio->page;
- struct lruvec *lruvec;
- struct address_space *swap_cache = NULL;
- unsigned long offset = 0;
- int i, nr_dropped = 0;
- unsigned int new_nr = 1 << new_order;
- int order = folio_order(folio);
- unsigned int nr = 1 << order;
-
- /* complete memcg works before add pages to LRU */
- split_page_memcg(head, order, new_order);
-
- if (folio_test_anon(folio) && folio_test_swapcache(folio)) {
- offset = swap_cache_index(folio->swap);
- swap_cache = swap_address_space(folio->swap);
- xa_lock(&swap_cache->i_pages);
- }
-
- /* lock lru list/PageCompound, ref frozen by page_ref_freeze */
- lruvec = folio_lruvec_lock(folio);
-
- folio_clear_has_hwpoisoned(folio);
-
- for (i = nr - new_nr; i >= new_nr; i -= new_nr) {
- struct folio *tail;
- __split_huge_page_tail(folio, i, lruvec, list, new_order);
- tail = page_folio(head + i);
- /* Some pages can be beyond EOF: drop them from page cache */
- if (tail->index >= end) {
- if (shmem_mapping(folio->mapping))
- nr_dropped += new_nr;
- else if (folio_test_clear_dirty(tail))
- folio_account_cleaned(tail,
- inode_to_wb(folio->mapping->host));
- __filemap_remove_folio(tail, NULL);
- folio_put(tail);
- } else if (!folio_test_anon(folio)) {
- __xa_store(&folio->mapping->i_pages, tail->index,
- tail, 0);
- } else if (swap_cache) {
- __xa_store(&swap_cache->i_pages, offset + i,
- tail, 0);
- }
- }
-
- 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, new_order);
- pgalloc_tag_split(folio, order, new_order);
-
- /* See comment in __split_huge_page_tail() */
- if (folio_test_anon(folio)) {
- /* Additional pin to swap cache */
- if (folio_test_swapcache(folio)) {
- folio_ref_add(folio, 1 + new_nr);
- xa_unlock(&swap_cache->i_pages);
- } else {
- folio_ref_inc(folio);
- }
- } else {
- /* Additional pin to page cache */
- folio_ref_add(folio, 1 + new_nr);
- xa_unlock(&folio->mapping->i_pages);
- }
- local_irq_enable();
-
- if (nr_dropped)
- shmem_uncharge(folio->mapping->host, nr_dropped);
- remap_page(folio, nr, PageAnon(head) ? RMP_USE_SHARED_ZEROPAGE : 0);
-
- /*
- * 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;
- struct folio *new_folio = page_folio(subpage);
- if (subpage == page)
- continue;
- folio_unlock(new_folio);
-
- /*
- * Subpages may be freed if there wasn't any mapping
- * like if add_to_swap() is running on a lru page that
- * had its mapping zapped. And freeing these pages
- * requires taking the lru_lock so we do the put_page
- * of the tail pages after the split is complete.
- */
- free_page_and_swap_cache(subpage);
- }
-}
-
/* Racy check whether the huge page can be split */
bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins)
{
--
2.47.2