From: Zi Yan <ziy@xxxxxxxxxx>
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 <ziy@xxxxxxxxxx>
---
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
