[PATCH 0/5] Split a folio to any lower order folios

[PATCH 0/5] Split a folio to any lower order folios

[Zi Yan]

From: Zi Yan <ziy@nvidia.com>

Hi all,

File folio supports any order and people would like to support flexible orders
for anonymous folio[1] too. Currently, split_huge_page() only splits a huge
page to order-0 pages, but splitting to orders higher than 0 is also useful.
This patchset adds support for splitting a huge page to any lower order pages
and uses it during folio truncate operations.

The patchset is on top of mm-everything-2023-03-19-21-50.

* Patch 1 and 2 add new_order parameter split_page_memcg() and
  split_page_owner() and prepare for upcoming changes.
* Patch 3 adds split_huge_page_to_list_to_order() to split a huge page
  to any lower order. The original split_huge_page_to_list() calls
  split_huge_page_to_list_to_order() with new_order = 0.
* Patch 4 uses split_huge_page_to_list_to_order() in large pagecache folio
  truncation instead of split the large folio all the way down to order-0.
* Patch 5 adds a test API to debugfs and test cases in
  split_huge_page_test selftests.

Comments and/or suggestions are welcome.

[1] https://lore.kernel.org/linux-mm/Y%2FblF0GIunm+pRIC@casper.infradead.org/

Zi Yan (5):
  mm: memcg: make memcg huge page split support any order split.
  mm: page_owner: add support for splitting to any order in split
    page_owner.
  mm: thp: split huge page to any lower order pages.
  mm: truncate: split huge page cache page to a non-zero order if
    possible.
  mm: huge_memory: enable debugfs to split huge pages to any order.

 include/linux/huge_mm.h                       |  10 +-
 include/linux/memcontrol.h                    |   5 +-
 include/linux/page_owner.h                    |  12 +-
 mm/huge_memory.c                              | 138 ++++++++---
 mm/memcontrol.c                               |   8 +-
 mm/page_alloc.c                               |   8 +-
 mm/page_owner.c                               |  11 +-
 mm/truncate.c                                 |  21 +-
 .../selftests/mm/split_huge_page_test.c       | 225 +++++++++++++++++-
 9 files changed, 368 insertions(+), 70 deletions(-)

-- 
2.39.2

[PATCH 1/5] mm: memcg: make memcg huge page split support any order split.

[Zi Yan]

From: Zi Yan <ziy@nvidia.com>

It sets memcg information for the pages after the split. A new parameter
new_nr is added to tell the number of subpages in the new page, always 1
for now. It prepares for upcoming changes to support split huge page to
any lower order.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/memcontrol.h | 5 +++--
 mm/huge_memory.c           | 2 +-
 mm/memcontrol.c            | 8 ++++----
 mm/page_alloc.c            | 2 +-
 4 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index aa69ea98e2d8..ee1021129142 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1151,7 +1151,7 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
 	rcu_read_unlock();
 }
 
-void split_page_memcg(struct page *head, unsigned int nr);
+void split_page_memcg(struct page *head, unsigned int nr, unsigned int new_nr);
 
 unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 						gfp_t gfp_mask,
@@ -1588,7 +1588,8 @@ void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx)
 {
 }
 
-static inline void split_page_memcg(struct page *head, unsigned int nr)
+static inline void split_page_memcg(struct page *head, unsigned int nr,
+						unsigned int new_nr)
 {
 }
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 81a5689806af..30e3e300c42e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2515,7 +2515,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 	int i;
 
 	/* complete memcg works before add pages to LRU */
-	split_page_memcg(head, nr);
+	split_page_memcg(head, nr, 1);
 
 	if (PageAnon(head) && PageSwapCache(head)) {
 		swp_entry_t entry = { .val = page_private(head) };
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 681e7528a714..8e505201baf0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3414,7 +3414,7 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size)
 /*
  * Because page_memcg(head) is not set on tails, set it now.
  */
-void split_page_memcg(struct page *head, unsigned int nr)
+void split_page_memcg(struct page *head, unsigned int nr, unsigned int new_nr)
 {
 	struct folio *folio = page_folio(head);
 	struct mem_cgroup *memcg = folio_memcg(folio);
@@ -3423,13 +3423,13 @@ void split_page_memcg(struct page *head, unsigned int nr)
 	if (mem_cgroup_disabled() || !memcg)
 		return;
 
-	for (i = 1; i < nr; i++)
+	for (i = new_nr; i < nr; i += new_nr)
 		folio_page(folio, i)->memcg_data = folio->memcg_data;
 
 	if (folio_memcg_kmem(folio))
-		obj_cgroup_get_many(__folio_objcg(folio), nr - 1);
+		obj_cgroup_get_many(__folio_objcg(folio), nr / new_nr - 1);
 	else
-		css_get_many(&memcg->css, nr - 1);
+		css_get_many(&memcg->css, nr / new_nr - 1);
 }
 
 #ifdef CONFIG_SWAP
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2e72fdbdd8db..59c2b6696698 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3531,7 +3531,7 @@ void split_page(struct page *page, unsigned int order)
 	for (i = 1; i < (1 << order); i++)
 		set_page_refcounted(page + i);
 	split_page_owner(page, 1 << order);
-	split_page_memcg(page, 1 << order);
+	split_page_memcg(page, 1 << order, 1);
 }
 EXPORT_SYMBOL_GPL(split_page);
 
-- 
2.39.2

[PATCH 2/5] mm: page_owner: add support for splitting to any order in split page_owner.

[Zi Yan]

From: Zi Yan <ziy@nvidia.com>

It adds a new_order parameter to set new page order in page owner and
uses old_order instead of nr to make the parameters look consistent.
It prepares for upcoming changes to support split huge page to any
lower order.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/page_owner.h | 12 +++++++-----
 mm/huge_memory.c           |  3 ++-
 mm/page_alloc.c            |  6 +++---
 mm/page_owner.c            | 11 ++++++-----
 4 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
index 119a0c9d2a8b..67d98de3d5a8 100644
--- a/include/linux/page_owner.h
+++ b/include/linux/page_owner.h
@@ -11,7 +11,8 @@ extern struct page_ext_operations page_owner_ops;
 extern void __reset_page_owner(struct page *page, unsigned short order);
 extern void __set_page_owner(struct page *page,
 			unsigned short order, gfp_t gfp_mask);
-extern void __split_page_owner(struct page *page, unsigned int nr);
+extern void __split_page_owner(struct page *page, unsigned short old_order,
+			unsigned short new_order);
 extern void __folio_copy_owner(struct folio *newfolio, struct folio *old);
 extern void __set_page_owner_migrate_reason(struct page *page, int reason);
 extern void __dump_page_owner(const struct page *page);
@@ -31,10 +32,11 @@ static inline void set_page_owner(struct page *page,
 		__set_page_owner(page, order, gfp_mask);
 }
 
-static inline void split_page_owner(struct page *page, unsigned int nr)
+static inline void split_page_owner(struct page *page, unsigned short old_order,
+			unsigned short new_order)
 {
 	if (static_branch_unlikely(&page_owner_inited))
-		__split_page_owner(page, nr);
+		__split_page_owner(page, old_order, new_order);
 }
 static inline void folio_copy_owner(struct folio *newfolio, struct folio *old)
 {
@@ -56,11 +58,11 @@ static inline void reset_page_owner(struct page *page, unsigned short order)
 {
 }
 static inline void set_page_owner(struct page *page,
-			unsigned int order, gfp_t gfp_mask)
+			unsigned short order, gfp_t gfp_mask)
 {
 }
 static inline void split_page_owner(struct page *page,
-			unsigned short order)
+			unsigned short old_order, unsigned short new_order)
 {
 }
 static inline void folio_copy_owner(struct folio *newfolio, struct folio *folio)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 30e3e300c42e..710189885402 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2511,6 +2511,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 	struct lruvec *lruvec;
 	struct address_space *swap_cache = NULL;
 	unsigned long offset = 0;
+	unsigned int order = thp_order(head);
 	unsigned int nr = thp_nr_pages(head);
 	int i;
 
@@ -2556,7 +2557,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 	unlock_page_lruvec(lruvec);
 	/* Caller disabled irqs, so they are still disabled here */
 
-	split_page_owner(head, nr);
+	split_page_owner(head, order, 0);
 
 	/* See comment in __split_huge_page_tail() */
 	if (PageAnon(head)) {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 59c2b6696698..ec85562865fb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3530,7 +3530,7 @@ void split_page(struct page *page, unsigned int order)
 
 	for (i = 1; i < (1 << order); i++)
 		set_page_refcounted(page + i);
-	split_page_owner(page, 1 << order);
+	split_page_owner(page, order, 0);
 	split_page_memcg(page, 1 << order, 1);
 }
 EXPORT_SYMBOL_GPL(split_page);
@@ -5746,8 +5746,8 @@ static void *make_alloc_exact(unsigned long addr, unsigned int order,
 		struct page *page = virt_to_page((void *)addr);
 		struct page *last = page + nr;
 
-		split_page_owner(page, 1 << order);
-		split_page_memcg(page, 1 << order);
+		split_page_owner(page, 1 << order, 1);
+		split_page_memcg(page, 1 << order, 1);
 		while (page < --last)
 			set_page_refcounted(last);
 
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 31169b3e7f06..33d1b6efe6a6 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -211,19 +211,20 @@ void __set_page_owner_migrate_reason(struct page *page, int reason)
 	page_ext_put(page_ext);
 }
 
-void __split_page_owner(struct page *page, unsigned int nr)
+void __split_page_owner(struct page *page, unsigned short old_order,
+			unsigned short new_order)
 {
-	int i;
+	int i, old_nr = 1 << old_order, new_nr = 1 << new_order;
 	struct page_ext *page_ext = page_ext_get(page);
 	struct page_owner *page_owner;
 
 	if (unlikely(!page_ext))
 		return;
 
-	for (i = 0; i < nr; i++) {
+	for (i = 0; i < old_nr; i += new_nr) {
+		page_ext = lookup_page_ext(page + i);
 		page_owner = get_page_owner(page_ext);
-		page_owner->order = 0;
-		page_ext = page_ext_next(page_ext);
+		page_owner->order = new_order;
 	}
 	page_ext_put(page_ext);
 }
-- 
2.39.2

Re: [PATCH 2/5] mm: page_owner: add support for splitting to any order in split page_owner.

[Michal Koutný]

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Hello.

On Mon, Mar 20, 2023 at 08:48:26PM -0400, Zi Yan <zi.yan@sent.com> wrote:
> @@ -5746,8 +5746,8 @@ static void *make_alloc_exact(unsigned long addr, unsigned int order,
>  		struct page *page = virt_to_page((void *)addr);
>  		struct page *last = page + nr;
>  
> -		split_page_owner(page, 1 << order);
> -		split_page_memcg(page, 1 << order);
> +		split_page_owner(page, 1 << order, 1);
> +		split_page_memcg(page, 1 << order, 1);

I think here should be

> +		split_page_owner(page, order, 0);
> +		split_page_memcg(page, 1 << order, 1);

because I was wondering why split_page_memcg() doesn't use orders too?
(E.g. it wouldn't work well if nr % new_new != 0).

Thanks,
Michal

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Re: [PATCH 2/5] mm: page_owner: add support for splitting to any order in split page_owner.

[Zi Yan]

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On 24 Mar 2023, at 11:17, Michal Koutný wrote:

> Hello.
>
> On Mon, Mar 20, 2023 at 08:48:26PM -0400, Zi Yan <zi.yan@sent.com> wrote:
>> @@ -5746,8 +5746,8 @@ static void *make_alloc_exact(unsigned long addr, unsigned int order,
>>  		struct page *page = virt_to_page((void *)addr);
>>  		struct page *last = page + nr;
>>
>> -		split_page_owner(page, 1 << order);
>> -		split_page_memcg(page, 1 << order);
>> +		split_page_owner(page, 1 << order, 1);
>> +		split_page_memcg(page, 1 << order, 1);
>
> I think here should be
>
>> +		split_page_owner(page, order, 0);
>> +		split_page_memcg(page, 1 << order, 1);
>
> because I was wondering why split_page_memcg() doesn't use orders too?
> (E.g. it wouldn't work well if nr % new_new != 0).

Thanks. Good point. I will make both use orders instead in next version.


--
Best Regards,
Yan, Zi

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[PATCH 3/5] mm: thp: split huge page to any lower order pages.

[Zi Yan]

From: Zi Yan <ziy@nvidia.com>

To split a THP to any lower order 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.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/huge_mm.h |  10 ++--
 mm/huge_memory.c        | 103 +++++++++++++++++++++++++++++-----------
 2 files changed, 82 insertions(+), 31 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 20284387b841..32c91e1b59cd 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -147,10 +147,11 @@ void prep_transhuge_page(struct page *page);
 void free_transhuge_page(struct page *page);
 
 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);
 
@@ -297,7 +298,8 @@ 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;
 }
@@ -397,7 +399,7 @@ static inline bool thp_migration_supported(void)
 static inline int split_folio_to_list(struct folio *folio,
 		struct list_head *list)
 {
-	return split_huge_page_to_list(&folio->page, list);
+	return split_huge_page_to_list_to_order(&folio->page, list, 0);
 }
 
 static inline int split_folio(struct folio *folio)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 710189885402..f119b9be33f2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2359,11 +2359,13 @@ 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;
+	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC;
 
 	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
 
+	if (folio_order(folio) >= HPAGE_PMD_ORDER)
+		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.
@@ -2395,7 +2397,6 @@ 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);
 
@@ -2416,9 +2417,10 @@ static void lru_add_page_tail(struct page *head, struct page *tail,
 }
 
 static void __split_huge_page_tail(struct page *head, int tail,
-		struct lruvec *lruvec, struct list_head *list)
+		struct lruvec *lruvec, struct list_head *list, unsigned int new_order)
 {
 	struct page *page_tail = head + tail;
+	unsigned long compound_head_flag = new_order ? (1L << PG_head) : 0;
 
 	VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
 
@@ -2451,6 +2453,7 @@ static void __split_huge_page_tail(struct page *head, int tail,
 			 (1L << PG_arch_3) |
 #endif
 			 (1L << PG_dirty) |
+			 compound_head_flag |
 			 LRU_GEN_MASK | LRU_REFS_MASK));
 
 	/* ->mapping in first and second tail page is replaced by other uses */
@@ -2483,10 +2486,15 @@ static void __split_huge_page_tail(struct page *head, int tail,
 	 * which needs correct compound_head().
 	 */
 	clear_compound_head(page_tail);
+	if (new_order) {
+		prep_compound_page(page_tail, new_order);
+		prep_transhuge_page(page_tail);
+	}
 
 	/* Finally unfreeze refcount. Additional reference from page cache. */
-	page_ref_unfreeze(page_tail, 1 + (!PageAnon(head) ||
-					  PageSwapCache(head)));
+	page_ref_unfreeze(page_tail, 1 + ((!PageAnon(head) ||
+					   PageSwapCache(head)) ?
+						thp_nr_pages(page_tail) : 0));
 
 	if (page_is_young(head))
 		set_page_young(page_tail);
@@ -2504,7 +2512,7 @@ static void __split_huge_page_tail(struct page *head, 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;
@@ -2513,10 +2521,11 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 	unsigned long offset = 0;
 	unsigned int order = thp_order(head);
 	unsigned int nr = thp_nr_pages(head);
+	unsigned int new_nr = 1 << new_order;
 	int i;
 
 	/* complete memcg works before add pages to LRU */
-	split_page_memcg(head, nr, 1);
+	split_page_memcg(head, nr, new_nr);
 
 	if (PageAnon(head) && PageSwapCache(head)) {
 		swp_entry_t entry = { .val = page_private(head) };
@@ -2531,14 +2540,14 @@ 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(head, i, lruvec, list);
+	for (i = nr - new_nr; i >= new_nr; i -= new_nr) {
+		__split_huge_page_tail(head, 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);
 
 			if (shmem_mapping(head->mapping))
-				shmem_uncharge(head->mapping->host, 1);
+				shmem_uncharge(head->mapping->host, new_nr);
 			else if (folio_test_clear_dirty(tail))
 				folio_account_cleaned(tail,
 					inode_to_wb(folio->mapping->host));
@@ -2548,29 +2557,38 @@ 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
+		set_compound_order(head, 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();
@@ -2583,7 +2601,14 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 		split_swap_cluster(entry);
 	}
 
-	for (i = 0; i < nr; i++) {
+	/*
+	 * set page to its compound_head when split to THPs, so that GUP pin and
+	 * PG_locked are transferred to the right after-split page
+	 */
+	if (new_order)
+		page = compound_head(page);
+
+	for (i = 0; i < nr; i += new_nr) {
 		struct page *subpage = head + i;
 		if (subpage == page)
 			continue;
@@ -2617,29 +2642,31 @@ 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.
  *
  * 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;
@@ -2649,6 +2676,18 @@ 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;
+	}
+
+	/* Split anonymous folio to non-zero order not support */
+	if (folio_test_anon(folio) && new_order) {
+		VM_WARN_ONCE(1, "Split anon folio to non-0 order not support");
+		return -EINVAL;
+	}
+
 	is_hzp = is_huge_zero_page(&folio->page);
 	VM_WARN_ON_ONCE_FOLIO(is_hzp, folio);
 	if (is_hzp)
@@ -2744,7 +2783,13 @@ 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) {
@@ -2754,14 +2799,18 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 			if (folio_test_swapbacked(folio)) {
 				__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
 							-nr);
-			} else {
+			} else if (!new_order) {
+				/*
+				 * Decrease THP stats only if split to normal
+				 * pages
+				 */
 				__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
 							-nr);
 				filemap_nr_thps_dec(mapping);
 			}
 		}
 
-		__split_huge_page(page, list, end);
+		__split_huge_page(page, list, end, new_order);
 		ret = 0;
 	} else {
 		spin_unlock(&ds_queue->split_queue_lock);
-- 
2.39.2

Re: [PATCH 3/5] mm: thp: split huge page to any lower order pages.

[Ryan Roberts]

Hi,

I'm working to enable large, variable-order folios for anonymous memory (see
RFC, replete with bugs at [1]). This patch set is going to be very useful to me.
But I have a few questions that I wonder if you can answer, below? I wonder if
they might relate to the bugs I'm seeing at [1].

[1] https://lore.kernel.org/linux-mm/20230317105802.2634004-1-ryan.roberts@arm.com/



On 21/03/2023 00:48, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> To split a THP to any lower order 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.
> 
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
>  include/linux/huge_mm.h |  10 ++--
>  mm/huge_memory.c        | 103 +++++++++++++++++++++++++++++-----------
>  2 files changed, 82 insertions(+), 31 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 20284387b841..32c91e1b59cd 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -147,10 +147,11 @@ void prep_transhuge_page(struct page *page);
>  void free_transhuge_page(struct page *page);
>  
>  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);
>  
> @@ -297,7 +298,8 @@ 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;
>  }
> @@ -397,7 +399,7 @@ static inline bool thp_migration_supported(void)
>  static inline int split_folio_to_list(struct folio *folio,
>  		struct list_head *list)
>  {
> -	return split_huge_page_to_list(&folio->page, list);
> +	return split_huge_page_to_list_to_order(&folio->page, list, 0);
>  }
>  
>  static inline int split_folio(struct folio *folio)
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 710189885402..f119b9be33f2 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2359,11 +2359,13 @@ 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;
> +	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC;
>  
>  	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>  
> +	if (folio_order(folio) >= HPAGE_PMD_ORDER)
> +		ttu_flags |= TTU_SPLIT_HUGE_PMD;
> +

Why have you changed the code so that this flag is added conditionally on the
folio being large enough? I've previously looked at this in the context of my
bug, and concluded that the consumer would ignore the flag if the folio wasn't
PMD mapped. Did I conclude incorrectly?


>  	/*
>  	 * Anon pages need migration entries to preserve them, but file
>  	 * pages can simply be left unmapped, then faulted back on demand.
> @@ -2395,7 +2397,6 @@ 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);
>  
> @@ -2416,9 +2417,10 @@ static void lru_add_page_tail(struct page *head, struct page *tail,
>  }
>  

[...]

> -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;
> @@ -2649,6 +2676,18 @@ 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;
> +	}

Why can't you split to order-1? I vaguely understand that some data is kept in
the first 3 struct pages, but I would naively expect the allocator to fail to
allocate compound pages of order-1 if it was a problem? My large anon folios
patch is currently allocating order-1 in some circumstances. Perhaps its related
to my bug?


> +
> +	/* Split anonymous folio to non-zero order not support */
> +	if (folio_test_anon(folio) && new_order) {
> +		VM_WARN_ONCE(1, "Split anon folio to non-0 order not support");
> +		return -EINVAL;
> +	}

Why don't you support this? What is special about anon folios that means this
code doesn't work for them?


Thanks,
Ryan



> +
>  	is_hzp = is_huge_zero_page(&folio->page);
>  	VM_WARN_ON_ONCE_FOLIO(is_hzp, folio);
>  	if (is_hzp)
> @@ -2744,7 +2783,13 @@ 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) {
> @@ -2754,14 +2799,18 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>  			if (folio_test_swapbacked(folio)) {
>  				__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
>  							-nr);
> -			} else {
> +			} else if (!new_order) {
> +				/*
> +				 * Decrease THP stats only if split to normal
> +				 * pages
> +				 */
>  				__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
>  							-nr);
>  				filemap_nr_thps_dec(mapping);
>  			}
>  		}
>  
> -		__split_huge_page(page, list, end);
> +		__split_huge_page(page, list, end, new_order);
>  		ret = 0;
>  	} else {
>  		spin_unlock(&ds_queue->split_queue_lock);

Re: [PATCH 3/5] mm: thp: split huge page to any lower order pages.

[Zi Yan]

[-- Attachment #1: Type: text/plain, Size: 8957 bytes --]

On 22 Mar 2023, at 3:55, Ryan Roberts wrote:

> Hi,
>
> I'm working to enable large, variable-order folios for anonymous memory (see
> RFC, replete with bugs at [1]). This patch set is going to be very useful to me.
> But I have a few questions that I wonder if you can answer, below? I wonder if
> they might relate to the bugs I'm seeing at [1].
>
> [1] https://lore.kernel.org/linux-mm/20230317105802.2634004-1-ryan.roberts@arm.com/
>
>
>
> On 21/03/2023 00:48, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>>
>> To split a THP to any lower order 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.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>>  include/linux/huge_mm.h |  10 ++--
>>  mm/huge_memory.c        | 103 +++++++++++++++++++++++++++++-----------
>>  2 files changed, 82 insertions(+), 31 deletions(-)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 20284387b841..32c91e1b59cd 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -147,10 +147,11 @@ void prep_transhuge_page(struct page *page);
>>  void free_transhuge_page(struct page *page);
>>
>>  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);
>>
>> @@ -297,7 +298,8 @@ 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;
>>  }
>> @@ -397,7 +399,7 @@ static inline bool thp_migration_supported(void)
>>  static inline int split_folio_to_list(struct folio *folio,
>>  		struct list_head *list)
>>  {
>> -	return split_huge_page_to_list(&folio->page, list);
>> +	return split_huge_page_to_list_to_order(&folio->page, list, 0);
>>  }
>>
>>  static inline int split_folio(struct folio *folio)
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 710189885402..f119b9be33f2 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2359,11 +2359,13 @@ 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;
>> +	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC;
>>
>>  	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>>
>> +	if (folio_order(folio) >= HPAGE_PMD_ORDER)
>> +		ttu_flags |= TTU_SPLIT_HUGE_PMD;
>> +
>
> Why have you changed the code so that this flag is added conditionally on the
> folio being large enough? I've previously looked at this in the context of my
> bug, and concluded that the consumer would ignore the flag if the folio wasn't
> PMD mapped. Did I conclude incorrectly?

Since if folio order is not larger than PMD order, there is no way of mapping
a PMD to the folio. Thus, TTU_SPLIT_HUGE_PMD does not make sense. Yes, the consumer
will not split any PMD, but will still do page table locks and mmu notifier
work, which cost unnecessary overheads.

I think I better change the if condition to folio_test_pmd_mappable().

>
>
>>  	/*
>>  	 * Anon pages need migration entries to preserve them, but file
>>  	 * pages can simply be left unmapped, then faulted back on demand.
>> @@ -2395,7 +2397,6 @@ 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);
>>
>> @@ -2416,9 +2417,10 @@ static void lru_add_page_tail(struct page *head, struct page *tail,
>>  }
>>
>
> [...]
>
>> -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;
>> @@ -2649,6 +2676,18 @@ 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;
>> +	}
>
> Why can't you split to order-1? I vaguely understand that some data is kept in
> the first 3 struct pages, but I would naively expect the allocator to fail to
> allocate compound pages of order-1 if it was a problem? My large anon folios
> patch is currently allocating order-1 in some circumstances. Perhaps its related
> to my bug?
>

Yes, some data is kept in first 3 struct pages, so order-1 THP is not possible.
The page allocator does not know this restriction, but still allocate an order-1
page. That might be related to your bug. You can have order-1 compound pages,
but it does not mean you can use them for THPs. AFAIK, slab uses order-1 compound
pages, but it does not store slab information on the 3rd struct page.

Basically, page allocator can allocate an order-N page, and it can be:
1. 2^N consecutive physical pages (not a compound page),
2. an order-N compound page,
3. an order-N THP (also an order-N compound page),
4. an order-N hugetlb page (also an order-N compound page).

For THP and hugetlb page, there are prep_transhuge_page() and
prep_new_hugetlb_folio() are called respectively after the page is allocated.
That makes them kinda subclasses of a compound page.

>
>> +
>> +	/* Split anonymous folio to non-zero order not support */
>> +	if (folio_test_anon(folio) && new_order) {
>> +		VM_WARN_ONCE(1, "Split anon folio to non-0 order not support");
>> +		return -EINVAL;
>> +	}
>
> Why don't you support this? What is special about anon folios that means this
> code doesn't work for them?

split_huge_page() code can split to non-0 order anon folios, but the rest of
the mm code might not have proper support yet.
That is why we need your patchset. :)

>
>
>> +
>>  	is_hzp = is_huge_zero_page(&folio->page);
>>  	VM_WARN_ON_ONCE_FOLIO(is_hzp, folio);
>>  	if (is_hzp)
>> @@ -2744,7 +2783,13 @@ 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) {
>> @@ -2754,14 +2799,18 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>>  			if (folio_test_swapbacked(folio)) {
>>  				__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
>>  							-nr);
>> -			} else {
>> +			} else if (!new_order) {
>> +				/*
>> +				 * Decrease THP stats only if split to normal
>> +				 * pages
>> +				 */
>>  				__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
>>  							-nr);
>>  				filemap_nr_thps_dec(mapping);
>>  			}
>>  		}
>>
>> -		__split_huge_page(page, list, end);
>> +		__split_huge_page(page, list, end, new_order);
>>  		ret = 0;
>>  	} else {
>>  		spin_unlock(&ds_queue->split_queue_lock);

--
Best Regards,
Yan, Zi

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Re: [PATCH 3/5] mm: thp: split huge page to any lower order pages.

[Ryan Roberts]

On 22/03/2023 14:27, Zi Yan wrote:
> On 22 Mar 2023, at 3:55, Ryan Roberts wrote:
> 
>> Hi,
>>
>> I'm working to enable large, variable-order folios for anonymous memory (see
>> RFC, replete with bugs at [1]). This patch set is going to be very useful to me.
>> But I have a few questions that I wonder if you can answer, below? I wonder if
>> they might relate to the bugs I'm seeing at [1].
>>
>> [1] https://lore.kernel.org/linux-mm/20230317105802.2634004-1-ryan.roberts@arm.com/
>>
>>
>>
>> On 21/03/2023 00:48, Zi Yan wrote:
>>> From: Zi Yan <ziy@nvidia.com>
>>>
>>> To split a THP to any lower order 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.
>>>
>>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>>> ---
>>>  include/linux/huge_mm.h |  10 ++--
>>>  mm/huge_memory.c        | 103 +++++++++++++++++++++++++++++-----------
>>>  2 files changed, 82 insertions(+), 31 deletions(-)
>>>
>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>> index 20284387b841..32c91e1b59cd 100644
>>> --- a/include/linux/huge_mm.h
>>> +++ b/include/linux/huge_mm.h
>>> @@ -147,10 +147,11 @@ void prep_transhuge_page(struct page *page);
>>>  void free_transhuge_page(struct page *page);
>>>
>>>  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);
>>>
>>> @@ -297,7 +298,8 @@ 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;
>>>  }
>>> @@ -397,7 +399,7 @@ static inline bool thp_migration_supported(void)
>>>  static inline int split_folio_to_list(struct folio *folio,
>>>  		struct list_head *list)
>>>  {
>>> -	return split_huge_page_to_list(&folio->page, list);
>>> +	return split_huge_page_to_list_to_order(&folio->page, list, 0);
>>>  }
>>>
>>>  static inline int split_folio(struct folio *folio)
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index 710189885402..f119b9be33f2 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -2359,11 +2359,13 @@ 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;
>>> +	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC;
>>>
>>>  	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>>>
>>> +	if (folio_order(folio) >= HPAGE_PMD_ORDER)
>>> +		ttu_flags |= TTU_SPLIT_HUGE_PMD;
>>> +
>>
>> Why have you changed the code so that this flag is added conditionally on the
>> folio being large enough? I've previously looked at this in the context of my
>> bug, and concluded that the consumer would ignore the flag if the folio wasn't
>> PMD mapped. Did I conclude incorrectly?
> 
> Since if folio order is not larger than PMD order, there is no way of mapping
> a PMD to the folio. Thus, TTU_SPLIT_HUGE_PMD does not make sense. Yes, the consumer
> will not split any PMD, but will still do page table locks and mmu notifier
> work, which cost unnecessary overheads.
> 
> I think I better change the if condition to folio_test_pmd_mappable().

Ahh, that makes sense - thanks.

> 
>>
>>
>>>  	/*
>>>  	 * Anon pages need migration entries to preserve them, but file
>>>  	 * pages can simply be left unmapped, then faulted back on demand.
>>> @@ -2395,7 +2397,6 @@ 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);
>>>
>>> @@ -2416,9 +2417,10 @@ static void lru_add_page_tail(struct page *head, struct page *tail,
>>>  }
>>>
>>
>> [...]
>>
>>> -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;
>>> @@ -2649,6 +2676,18 @@ 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;
>>> +	}
>>
>> Why can't you split to order-1? I vaguely understand that some data is kept in
>> the first 3 struct pages, but I would naively expect the allocator to fail to
>> allocate compound pages of order-1 if it was a problem? My large anon folios
>> patch is currently allocating order-1 in some circumstances. Perhaps its related
>> to my bug?
>>
> 
> Yes, some data is kept in first 3 struct pages, so order-1 THP is not possible.
> The page allocator does not know this restriction, but still allocate an order-1
> page. That might be related to your bug. You can have order-1 compound pages,
> but it does not mean you can use them for THPs. AFAIK, slab uses order-1 compound
> pages, but it does not store slab information on the 3rd struct page.
> 
> Basically, page allocator can allocate an order-N page, and it can be:
> 1. 2^N consecutive physical pages (not a compound page),
> 2. an order-N compound page,
> 3. an order-N THP (also an order-N compound page),
> 4. an order-N hugetlb page (also an order-N compound page).
> 
> For THP and hugetlb page, there are prep_transhuge_page() and
> prep_new_hugetlb_folio() are called respectively after the page is allocated.
> That makes them kinda subclasses of a compound page.

I've been staring at this code most of the day, and just concluded that this is
exactly my bug. split_huge_page() was trying to split my order-1 page and
scribbling over the _deferred_list in a neighboring struct page. So thanks for
posting the patch and triggering the thought! And thanks for taking the time to
explain all this.

> 
>>
>>> +
>>> +	/* Split anonymous folio to non-zero order not support */
>>> +	if (folio_test_anon(folio) && new_order) {
>>> +		VM_WARN_ONCE(1, "Split anon folio to non-0 order not support");
>>> +		return -EINVAL;
>>> +	}
>>
>> Why don't you support this? What is special about anon folios that means this
>> code doesn't work for them?
> 
> split_huge_page() code can split to non-0 order anon folios, but the rest of
> the mm code might not have proper support yet.
> That is why we need your patchset. :)
> 
>>
>>
>>> +
>>>  	is_hzp = is_huge_zero_page(&folio->page);
>>>  	VM_WARN_ON_ONCE_FOLIO(is_hzp, folio);
>>>  	if (is_hzp)
>>> @@ -2744,7 +2783,13 @@ 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) {
>>> @@ -2754,14 +2799,18 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>>>  			if (folio_test_swapbacked(folio)) {
>>>  				__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
>>>  							-nr);
>>> -			} else {
>>> +			} else if (!new_order) {
>>> +				/*
>>> +				 * Decrease THP stats only if split to normal
>>> +				 * pages
>>> +				 */
>>>  				__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
>>>  							-nr);
>>>  				filemap_nr_thps_dec(mapping);
>>>  			}
>>>  		}
>>>
>>> -		__split_huge_page(page, list, end);
>>> +		__split_huge_page(page, list, end, new_order);
>>>  		ret = 0;
>>>  	} else {
>>>  		spin_unlock(&ds_queue->split_queue_lock);
> 
> --
> Best Regards,
> Yan, Zi

[PATCH 4/5] mm: truncate: split huge page cache page to a non-zero order if possible.

[Zi Yan]

From: Zi Yan <ziy@nvidia.com>

To minimize the number of pages after a huge page truncation, we do not
need to split it all the way down to order-0. The huge page has at most
three parts, the part before offset, the part to be truncated, the part
remaining at the end. Find the greatest common divisor of them to
calculate the new page order from it, so we can split the huge
page to this order and keep the remaining pages as large and as few as
possible.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/truncate.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/mm/truncate.c b/mm/truncate.c
index 86de31ed4d32..817efd5e94b4 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -22,6 +22,7 @@
 #include <linux/buffer_head.h>	/* grr. try_to_release_page */
 #include <linux/shmem_fs.h>
 #include <linux/rmap.h>
+#include <linux/gcd.h>
 #include "internal.h"
 
 /*
@@ -211,7 +212,8 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio)
 bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
 {
 	loff_t pos = folio_pos(folio);
-	unsigned int offset, length;
+	unsigned int offset, length, remaining;
+	unsigned int new_order = folio_order(folio);
 
 	if (pos < start)
 		offset = start - pos;
@@ -222,6 +224,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
 		length = length - offset;
 	else
 		length = end + 1 - pos - offset;
+	remaining = folio_size(folio) - offset - length;
 
 	folio_wait_writeback(folio);
 	if (length == folio_size(folio)) {
@@ -236,11 +239,25 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
 	 */
 	folio_zero_range(folio, offset, length);
 
+	/*
+	 * Use the greatest common divisor of offset, length, and remaining
+	 * as the smallest page size and compute the new order from it. So we
+	 * can truncate a subpage as large as possible. Round up gcd to
+	 * PAGE_SIZE, otherwise ilog2 can give -1 when gcd/PAGE_SIZE is 0.
+	 */
+	new_order = ilog2(round_up(gcd(gcd(offset, length), remaining),
+				   PAGE_SIZE) / PAGE_SIZE);
+
+	/* order-1 THP not supported, downgrade to order-0 */
+	if (new_order == 1)
+		new_order = 0;
+
+
 	if (folio_has_private(folio))
 		folio_invalidate(folio, offset, length);
 	if (!folio_test_large(folio))
 		return true;
-	if (split_folio(folio) == 0)
+	if (split_huge_page_to_list_to_order(&folio->page, NULL, new_order) == 0)
 		return true;
 	if (folio_test_dirty(folio))
 		return false;
-- 
2.39.2

[PATCH 5/5] mm: huge_memory: enable debugfs to split huge pages to any order.

[Zi Yan]

From: Zi Yan <ziy@nvidia.com>

It is used to test split_huge_page_to_list_to_order for pagecache THPs.
Also add test cases for split_huge_page_to_list_to_order via both
debugfs, truncating a file, and punching holes in a file.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/huge_memory.c                              |  34 ++-
 .../selftests/mm/split_huge_page_test.c       | 225 +++++++++++++++++-
 2 files changed, 242 insertions(+), 17 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f119b9be33f2..cadb13e3224f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3024,7 +3024,7 @@ static inline bool vma_not_suitable_for_thp_split(struct vm_area_struct *vma)
 }
 
 static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
-				unsigned long vaddr_end)
+				unsigned long vaddr_end, unsigned int new_order)
 {
 	int ret = 0;
 	struct task_struct *task;
@@ -3086,13 +3086,19 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
 			goto next;
 
 		total++;
-		if (!can_split_folio(page_folio(page), NULL))
+		/*
+		 * For folios with private, split_huge_page_to_list_to_order()
+		 * will try to drop it before split and then check if the folio
+		 * can be split or not. So skip the check here.
+		 */
+		if (!folio_test_private(page_folio(page)) &&
+		    !can_split_folio(page_folio(page), NULL))
 			goto next;
 
 		if (!trylock_page(page))
 			goto next;
 
-		if (!split_huge_page(page))
+		if (!split_huge_page_to_list_to_order(page, NULL, new_order))
 			split++;
 
 		unlock_page(page);
@@ -3110,7 +3116,7 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
 }
 
 static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
-				pgoff_t off_end)
+				pgoff_t off_end, unsigned int new_order)
 {
 	struct filename *file;
 	struct file *candidate;
@@ -3149,7 +3155,7 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
 		if (!folio_trylock(folio))
 			goto next;
 
-		if (!split_folio(folio))
+		if (!split_huge_page_to_list_to_order(&folio->page, NULL, new_order))
 			split++;
 
 		folio_unlock(folio);
@@ -3174,10 +3180,14 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
 {
 	static DEFINE_MUTEX(split_debug_mutex);
 	ssize_t ret;
-	/* hold pid, start_vaddr, end_vaddr or file_path, off_start, off_end */
+	/*
+	 * hold pid, start_vaddr, end_vaddr, new_order or
+	 * file_path, off_start, off_end, new_order
+	 */
 	char input_buf[MAX_INPUT_BUF_SZ];
 	int pid;
 	unsigned long vaddr_start, vaddr_end;
+	unsigned int new_order = 0;
 
 	ret = mutex_lock_interruptible(&split_debug_mutex);
 	if (ret)
@@ -3206,29 +3216,29 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
 			goto out;
 		}
 
-		ret = sscanf(buf, "0x%lx,0x%lx", &off_start, &off_end);
-		if (ret != 2) {
+		ret = sscanf(buf, "0x%lx,0x%lx,%d", &off_start, &off_end, &new_order);
+		if (ret != 2 && ret != 3) {
 			ret = -EINVAL;
 			goto out;
 		}
-		ret = split_huge_pages_in_file(file_path, off_start, off_end);
+		ret = split_huge_pages_in_file(file_path, off_start, off_end, new_order);
 		if (!ret)
 			ret = input_len;
 
 		goto out;
 	}
 
-	ret = sscanf(input_buf, "%d,0x%lx,0x%lx", &pid, &vaddr_start, &vaddr_end);
+	ret = sscanf(input_buf, "%d,0x%lx,0x%lx,%d", &pid, &vaddr_start, &vaddr_end, &new_order);
 	if (ret == 1 && pid == 1) {
 		split_huge_pages_all();
 		ret = strlen(input_buf);
 		goto out;
-	} else if (ret != 3) {
+	} else if (ret != 3 && ret != 4) {
 		ret = -EINVAL;
 		goto out;
 	}
 
-	ret = split_huge_pages_pid(pid, vaddr_start, vaddr_end);
+	ret = split_huge_pages_pid(pid, vaddr_start, vaddr_end, new_order);
 	if (!ret)
 		ret = strlen(input_buf);
 out:
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index b8558c7f1a39..cbb5e6893cbf 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -16,6 +16,7 @@
 #include <sys/mount.h>
 #include <malloc.h>
 #include <stdbool.h>
+#include <time.h>
 #include "vm_util.h"
 
 uint64_t pagesize;
@@ -23,10 +24,12 @@ unsigned int pageshift;
 uint64_t pmd_pagesize;
 
 #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
+#define SMAP_PATH "/proc/self/smaps"
+#define THP_FS_PATH "/mnt/thp_fs"
 #define INPUT_MAX 80
 
-#define PID_FMT "%d,0x%lx,0x%lx"
-#define PATH_FMT "%s,0x%lx,0x%lx"
+#define PID_FMT "%d,0x%lx,0x%lx,%d"
+#define PATH_FMT "%s,0x%lx,0x%lx,%d"
 
 #define PFN_MASK     ((1UL<<55)-1)
 #define KPF_THP      (1UL<<22)
@@ -113,7 +116,7 @@ void split_pmd_thp(void)
 
 	/* split all THPs */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
-		(uint64_t)one_page + len);
+		(uint64_t)one_page + len, 0);
 
 	for (i = 0; i < len; i++)
 		if (one_page[i] != (char)i) {
@@ -203,7 +206,7 @@ void split_pte_mapped_thp(void)
 
 	/* split all remapped THPs */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)pte_mapped,
-		      (uint64_t)pte_mapped + pagesize * 4);
+		      (uint64_t)pte_mapped + pagesize * 4, 0);
 
 	/* smap does not show THPs after mremap, use kpageflags instead */
 	thp_size = 0;
@@ -269,7 +272,7 @@ void split_file_backed_thp(void)
 	}
 
 	/* split the file-backed THP */
-	write_debugfs(PATH_FMT, testfile, pgoff_start, pgoff_end);
+	write_debugfs(PATH_FMT, testfile, pgoff_start, pgoff_end, 0);
 
 	status = unlink(testfile);
 	if (status)
@@ -290,20 +293,232 @@ void split_file_backed_thp(void)
 	printf("file-backed THP split test done, please check dmesg for more information\n");
 }
 
+void create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd, char **addr)
+{
+	size_t i;
+	int dummy;
+
+	srand(time(NULL));
+
+	*fd = open(testfile, O_CREAT | O_RDWR, 0664);
+	if (*fd == -1) {
+		perror("Failed to create a file at "THP_FS_PATH);
+		exit(EXIT_FAILURE);
+	}
+
+	for (i = 0; i < fd_size; i++) {
+		unsigned char byte = (unsigned char)i;
+
+		write(*fd, &byte, sizeof(byte));
+	}
+	close(*fd);
+	sync();
+	*fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
+	if (*fd == -1) {
+		perror("open drop_caches");
+		goto err_out_unlink;
+	}
+	if (write(*fd, "3", 1) != 1) {
+		perror("write to drop_caches");
+		goto err_out_unlink;
+	}
+	close(*fd);
+
+	*fd = open(testfile, O_RDWR);
+	if (*fd == -1) {
+		perror("Failed to open a file at "THP_FS_PATH);
+		goto err_out_unlink;
+	}
+
+	*addr = mmap(NULL, fd_size, PROT_READ|PROT_WRITE, MAP_SHARED, *fd, 0);
+	if (*addr == (char *)-1) {
+		perror("cannot mmap");
+		goto err_out_close;
+	}
+	madvise(*addr, fd_size, MADV_HUGEPAGE);
+
+	for (size_t i = 0; i < fd_size; i++)
+		dummy += *(*addr + i);
+
+	if (!check_huge_file(*addr, fd_size / pmd_pagesize, pmd_pagesize)) {
+		printf("No pagecache THP generated, please mount a filesystem supporting pagecache THP at "THP_FS_PATH"\n");
+		goto err_out_close;
+	}
+	return;
+err_out_close:
+	close(*fd);
+err_out_unlink:
+	unlink(testfile);
+	exit(EXIT_FAILURE);
+}
+
+void split_thp_in_pagecache_to_order(size_t fd_size, int order)
+{
+	int fd;
+	char *addr;
+	size_t i;
+	const char testfile[] = THP_FS_PATH "/test";
+	int err = 0;
+
+	create_pagecache_thp_and_fd(testfile, fd_size, &fd, &addr);
+
+	printf("split %ld kB PMD-mapped pagecache page to order %d ... ", fd_size >> 10, order);
+	write_debugfs(PID_FMT, getpid(), (uint64_t)addr, (uint64_t)addr + fd_size, order);
+
+	for (i = 0; i < fd_size; i++)
+		if (*(addr + i) != (char)i) {
+			printf("%lu byte corrupted in the file\n", i);
+			err = EXIT_FAILURE;
+			goto out;
+		}
+
+	if (!check_huge_file(addr, 0, pmd_pagesize)) {
+		printf("Still FilePmdMapped not split\n");
+		err = EXIT_FAILURE;
+		goto out;
+	}
+
+	printf("done\n");
+out:
+	close(fd);
+	unlink(testfile);
+	if (err)
+		exit(err);
+}
+
+void truncate_thp_in_pagecache_to_order(size_t fd_size, int order)
+{
+	int fd;
+	char *addr;
+	size_t i;
+	const char testfile[] = THP_FS_PATH "/test";
+	int err = 0;
+
+	create_pagecache_thp_and_fd(testfile, fd_size, &fd, &addr);
+
+	printf("truncate %ld kB PMD-mapped pagecache page to size %lu kB ... ",
+		fd_size >> 10, 4UL << order);
+	ftruncate(fd, pagesize << order);
+
+	for (i = 0; i < (pagesize << order); i++)
+		if (*(addr + i) != (char)i) {
+			printf("%lu byte corrupted in the file\n", i);
+			err = EXIT_FAILURE;
+			goto out;
+		}
+
+	if (!check_huge_file(addr, 0, pmd_pagesize)) {
+		printf("Still FilePmdMapped not split after truncate\n");
+		err = EXIT_FAILURE;
+		goto out;
+	}
+
+	printf("done\n");
+out:
+	close(fd);
+	unlink(testfile);
+	if (err)
+		exit(err);
+}
+
+void punch_hole_in_pagecache_thp(size_t fd_size, off_t offset[], off_t len[],
+			int n, int num_left_thps)
+{
+	int fd, j;
+	char *addr;
+	size_t i;
+	const char testfile[] = THP_FS_PATH "/test";
+	int err = 0;
+
+	create_pagecache_thp_and_fd(testfile, fd_size, &fd, &addr);
+
+	for (j = 0; j < n; j++) {
+		printf("punch a hole to %ld kB PMD-mapped pagecache page at addr: %lx, offset %ld, and len %ld ...\n",
+			fd_size >> 10, (unsigned long)addr, offset[j], len[j]);
+		fallocate(fd, FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE, offset[j], len[j]);
+	}
+
+	for (i = 0; i < fd_size; i++) {
+		int in_hole = 0;
+
+		for (j = 0; j < n; j++)
+			if (i >= offset[j] && i < (offset[j] + len[j])) {
+				in_hole = 1;
+				break;
+			}
+
+		if (in_hole) {
+			if (*(addr + i)) {
+				printf("%lu byte non-zero after punch\n", i);
+				err = EXIT_FAILURE;
+				goto out;
+			}
+			continue;
+		}
+		if (*(addr + i) != (char)i) {
+			printf("%lu byte corrupted in the file\n", i);
+			err = EXIT_FAILURE;
+			goto out;
+		}
+	}
+
+	if (!check_huge_file(addr, num_left_thps, pmd_pagesize)) {
+		printf("Still FilePmdMapped not split after punch\n");
+		goto out;
+	}
+	printf("done\n");
+out:
+	close(fd);
+	unlink(testfile);
+	if (err)
+		exit(err);
+}
+
 int main(int argc, char **argv)
 {
+	int i;
+	size_t fd_size;
+	off_t offset[2], len[2];
+
 	if (geteuid() != 0) {
 		printf("Please run the benchmark as root\n");
 		exit(EXIT_FAILURE);
 	}
 
+	setbuf(stdout, NULL);
+
 	pagesize = getpagesize();
 	pageshift = ffs(pagesize) - 1;
 	pmd_pagesize = read_pmd_pagesize();
+	fd_size = 2 * pmd_pagesize;
 
 	split_pmd_thp();
 	split_pte_mapped_thp();
 	split_file_backed_thp();
 
+	for (i = 8; i >= 0; i--)
+		if (i != 1)
+			split_thp_in_pagecache_to_order(fd_size, i);
+
+	/*
+	 * for i is 1, truncate code in the kernel should create order-0 pages
+	 * instead of order-1 THPs, since order-1 THP is not supported. No error
+	 * is expected.
+	 */
+	for (i = 8; i >= 0; i--)
+		truncate_thp_in_pagecache_to_order(fd_size, i);
+
+	offset[0] = 123;
+	offset[1] = 4 * pagesize;
+	len[0] = 200 * pagesize;
+	len[1] = 16 * pagesize;
+	punch_hole_in_pagecache_thp(fd_size, offset, len, 2, 1);
+
+	offset[0] = 259 * pagesize + pagesize / 2;
+	offset[1] = 33 * pagesize;
+	len[0] = 129 * pagesize;
+	len[1] = 16 * pagesize;
+	punch_hole_in_pagecache_thp(fd_size, offset, len, 2, 1);
+
 	return 0;
 }
-- 
2.39.2