[RFC PATCH 00/11] Remove READ_ONLY_THP_FOR_FS

[RFC PATCH 00/11] Remove READ_ONLY_THP_FOR_FS

[Zi Yan]

Hi all,

After Willy's heads-up on the removal of CONFIG_READ_ONLY_THP_FOR_FS[1].
This patchset is an attempt of removing it.

The patchset does the removal in the following steps:
1. remove READ_ONLY_THP_FOR_FS Kconfig
2. remove collapse_file() code on READ_ONLY_THP_FOR_FS
3. remove filemap_nr_thps*() functions
4. remove file_thp_enabled()
5. remove related folio splittable checks
6. replace try_folio_split_to_order() with folio_split() in
   truncate_inode_partial_folio().
6. remove related fs code
7. clean up selftests code

It seems that NR_FILE_THPS is also used for fs with large folio support,
so it is kept.

Let me know if I miss anything. Comments and suggestions are welcome.

Link: https://lore.kernel.org/all/aTJg9vOijOGVTnVt@casper.infradead.org/ [1]

Zi Yan (11):
  mm: remove READ_ONLY_THP_FOR_FS Kconfig option
  mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()
  mm: remove filemap_nr_thps*() functions
  mm/huge_memory: remove file_thp_enabled() and its caller.
  mm/huge_memory: remove folio split check for READ_ONLY_THP_FOR_FS
  mm/truncate: use folio_split() in truncate_inode_partial_folio()
  fs: remove nr_thp from struct address_space
  fs: remove READ_ONLY_THP_FOR_FS code
  fs/btrfs: remove a comment referring to READ_ONLY_THP_FOR_FS
  selftests/mm: remove READ_ONLY_THP_FOR_FS test in khugepaged
  selftests/mm: remove READ_ONLY_THP_FOR_FS test in guard-regions

 fs/btrfs/defrag.c                          |   3 -
 fs/inode.c                                 |   3 -
 fs/open.c                                  |  27 ---
 include/linux/fs.h                         |   5 -
 include/linux/huge_mm.h                    |  28 ---
 include/linux/pagemap.h                    |  29 ---
 mm/Kconfig                                 |  11 --
 mm/filemap.c                               |   1 -
 mm/huge_memory.c                           |  44 -----
 mm/khugepaged.c                            | 159 ++++-------------
 mm/truncate.c                              |   8 +-
 tools/testing/selftests/mm/guard-regions.c | 148 +---------------
 tools/testing/selftests/mm/khugepaged.c    | 197 +--------------------
 13 files changed, 42 insertions(+), 621 deletions(-)

-- 
2.43.0

[RFC PATCH 01/11] mm: remove READ_ONLY_THP_FOR_FS Kconfig option

[Zi Yan]

No one will be able to use it, so the related code can be removed in the
coming commits.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/Kconfig | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index bd283958d675..408fc7b82233 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -937,17 +937,6 @@ config THP_SWAP
 
 	  For selection by architectures with reasonable THP sizes.
 
-config READ_ONLY_THP_FOR_FS
-	bool "Read-only THP for filesystems (EXPERIMENTAL)"
-	depends on TRANSPARENT_HUGEPAGE
-
-	help
-	  Allow khugepaged to put read-only file-backed pages in THP.
-
-	  This is marked experimental because it is a new feature. Write
-	  support of file THPs will be developed in the next few release
-	  cycles.
-
 config NO_PAGE_MAPCOUNT
 	bool "No per-page mapcount (EXPERIMENTAL)"
 	help
-- 
2.43.0

[RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Zi Yan]

READ_ONLY_THP_FOR_FS is no longer present, remove corresponding code.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/khugepaged.c | 159 +++++++++++-------------------------------------
 1 file changed, 34 insertions(+), 125 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b2ac28ddd480..39f0b8959535 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1899,7 +1899,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 	int nr_none = 0;
 	bool is_shmem = shmem_file(file);
 
-	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
+	VM_WARN_ON_ONCE(!is_shmem);
 	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
 
 	result = alloc_charge_folio(&new_folio, mm, cc);
@@ -1909,8 +1909,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 	mapping_set_update(&xas, mapping);
 
 	__folio_set_locked(new_folio);
-	if (is_shmem)
-		__folio_set_swapbacked(new_folio);
+	__folio_set_swapbacked(new_folio);
 	new_folio->index = start;
 	new_folio->mapping = mapping;
 
@@ -1935,83 +1934,39 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 		folio = xas_load(&xas);
 
 		VM_BUG_ON(index != xas.xa_index);
-		if (is_shmem) {
-			if (!folio) {
-				/*
-				 * Stop if extent has been truncated or
-				 * hole-punched, and is now completely
-				 * empty.
-				 */
-				if (index == start) {
-					if (!xas_next_entry(&xas, end - 1)) {
-						result = SCAN_TRUNCATED;
-						goto xa_locked;
-					}
+		if (!folio) {
+			/*
+			 * Stop if extent has been truncated or
+			 * hole-punched, and is now completely
+			 * empty.
+			 */
+			if (index == start) {
+				if (!xas_next_entry(&xas, end - 1)) {
+					result = SCAN_TRUNCATED;
+					goto xa_locked;
 				}
-				nr_none++;
-				index++;
-				continue;
 			}
+			nr_none++;
+			index++;
+			continue;
+		}
 
-			if (xa_is_value(folio) || !folio_test_uptodate(folio)) {
-				xas_unlock_irq(&xas);
-				/* swap in or instantiate fallocated page */
-				if (shmem_get_folio(mapping->host, index, 0,
-						&folio, SGP_NOALLOC)) {
-					result = SCAN_FAIL;
-					goto xa_unlocked;
-				}
-				/* drain lru cache to help folio_isolate_lru() */
-				lru_add_drain();
-			} else if (folio_trylock(folio)) {
-				folio_get(folio);
-				xas_unlock_irq(&xas);
-			} else {
-				result = SCAN_PAGE_LOCK;
-				goto xa_locked;
-			}
-		} else {	/* !is_shmem */
-			if (!folio || xa_is_value(folio)) {
-				xas_unlock_irq(&xas);
-				page_cache_sync_readahead(mapping, &file->f_ra,
-							  file, index,
-							  end - index);
-				/* drain lru cache to help folio_isolate_lru() */
-				lru_add_drain();
-				folio = filemap_lock_folio(mapping, index);
-				if (IS_ERR(folio)) {
-					result = SCAN_FAIL;
-					goto xa_unlocked;
-				}
-			} else if (folio_test_dirty(folio)) {
-				/*
-				 * khugepaged only works on read-only fd,
-				 * so this page is dirty because it hasn't
-				 * been flushed since first write. There
-				 * won't be new dirty pages.
-				 *
-				 * Trigger async flush here and hope the
-				 * writeback is done when khugepaged
-				 * revisits this page.
-				 *
-				 * This is a one-off situation. We are not
-				 * forcing writeback in loop.
-				 */
-				xas_unlock_irq(&xas);
-				filemap_flush(mapping);
-				result = SCAN_PAGE_DIRTY_OR_WRITEBACK;
-				goto xa_unlocked;
-			} else if (folio_test_writeback(folio)) {
-				xas_unlock_irq(&xas);
-				result = SCAN_PAGE_DIRTY_OR_WRITEBACK;
+		if (xa_is_value(folio) || !folio_test_uptodate(folio)) {
+			xas_unlock_irq(&xas);
+			/* swap in or instantiate fallocated page */
+			if (shmem_get_folio(mapping->host, index, 0,
+					&folio, SGP_NOALLOC)) {
+				result = SCAN_FAIL;
 				goto xa_unlocked;
-			} else if (folio_trylock(folio)) {
-				folio_get(folio);
-				xas_unlock_irq(&xas);
-			} else {
-				result = SCAN_PAGE_LOCK;
-				goto xa_locked;
 			}
+			/* drain lru cache to help folio_isolate_lru() */
+			lru_add_drain();
+		} else if (folio_trylock(folio)) {
+			folio_get(folio);
+			xas_unlock_irq(&xas);
+		} else {
+			result = SCAN_PAGE_LOCK;
+			goto xa_locked;
 		}
 
 		/*
@@ -2041,17 +1996,6 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 			goto out_unlock;
 		}
 
-		if (!is_shmem && (folio_test_dirty(folio) ||
-				  folio_test_writeback(folio))) {
-			/*
-			 * khugepaged only works on read-only fd, so this
-			 * folio is dirty because it hasn't been flushed
-			 * since first write.
-			 */
-			result = SCAN_PAGE_DIRTY_OR_WRITEBACK;
-			goto out_unlock;
-		}
-
 		if (!folio_isolate_lru(folio)) {
 			result = SCAN_DEL_PAGE_LRU;
 			goto out_unlock;
@@ -2101,21 +2045,6 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 		goto xa_unlocked;
 	}
 
-	if (!is_shmem) {
-		filemap_nr_thps_inc(mapping);
-		/*
-		 * Paired with the fence in do_dentry_open() -> get_write_access()
-		 * to ensure i_writecount is up to date and the update to nr_thps
-		 * is visible. Ensures the page cache will be truncated if the
-		 * file is opened writable.
-		 */
-		smp_mb();
-		if (inode_is_open_for_write(mapping->host)) {
-			result = SCAN_FAIL;
-			filemap_nr_thps_dec(mapping);
-		}
-	}
-
 xa_locked:
 	xas_unlock_irq(&xas);
 xa_unlocked:
@@ -2224,12 +2153,8 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 		xas_lock_irq(&xas);
 	}
 
-	if (is_shmem) {
-		lruvec_stat_mod_folio(new_folio, NR_SHMEM, HPAGE_PMD_NR);
-		lruvec_stat_mod_folio(new_folio, NR_SHMEM_THPS, HPAGE_PMD_NR);
-	} else {
-		lruvec_stat_mod_folio(new_folio, NR_FILE_THPS, HPAGE_PMD_NR);
-	}
+	lruvec_stat_mod_folio(new_folio, NR_SHMEM, HPAGE_PMD_NR);
+	lruvec_stat_mod_folio(new_folio, NR_SHMEM_THPS, HPAGE_PMD_NR);
 	lruvec_stat_mod_folio(new_folio, NR_FILE_PAGES, HPAGE_PMD_NR);
 
 	/*
@@ -2240,8 +2165,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 	folio_mark_uptodate(new_folio);
 	folio_ref_add(new_folio, HPAGE_PMD_NR - 1);
 
-	if (is_shmem)
-		folio_mark_dirty(new_folio);
+	folio_mark_dirty(new_folio);
 	folio_add_lru(new_folio);
 
 	/* Join all the small entries into a single multi-index entry. */
@@ -2266,9 +2190,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 		list_del(&folio->lru);
 		lruvec_stat_mod_folio(folio, NR_FILE_PAGES,
 				      -folio_nr_pages(folio));
-		if (is_shmem)
-			lruvec_stat_mod_folio(folio, NR_SHMEM,
-					      -folio_nr_pages(folio));
+		lruvec_stat_mod_folio(folio, NR_SHMEM, -folio_nr_pages(folio));
 		folio->mapping = NULL;
 		folio_clear_active(folio);
 		folio_clear_unevictable(folio);
@@ -2293,19 +2215,6 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 		folio_putback_lru(folio);
 		folio_put(folio);
 	}
-	/*
-	 * Undo the updates of filemap_nr_thps_inc for non-SHMEM
-	 * file only. This undo is not needed unless failure is
-	 * due to SCAN_COPY_MC.
-	 */
-	if (!is_shmem && result == SCAN_COPY_MC) {
-		filemap_nr_thps_dec(mapping);
-		/*
-		 * Paired with the fence in do_dentry_open() -> get_write_access()
-		 * to ensure the update to nr_thps is visible.
-		 */
-		smp_mb();
-	}
 
 	new_folio->mapping = NULL;
 
-- 
2.43.0

[RFC PATCH 03/11] mm: remove filemap_nr_thps*() functions

[Zi Yan]

They are used by READ_ONLY_THP_FOR_FS and no longer needed.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/pagemap.h | 29 -----------------------------
 mm/filemap.c            |  1 -
 mm/huge_memory.c        |  1 -
 3 files changed, 31 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ec442af3f886..dad3f8846cdc 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -530,35 +530,6 @@ static inline size_t mapping_max_folio_size(const struct address_space *mapping)
 	return PAGE_SIZE << mapping_max_folio_order(mapping);
 }
 
-static inline int filemap_nr_thps(const struct address_space *mapping)
-{
-#ifdef CONFIG_READ_ONLY_THP_FOR_FS
-	return atomic_read(&mapping->nr_thps);
-#else
-	return 0;
-#endif
-}
-
-static inline void filemap_nr_thps_inc(struct address_space *mapping)
-{
-#ifdef CONFIG_READ_ONLY_THP_FOR_FS
-	if (!mapping_large_folio_support(mapping))
-		atomic_inc(&mapping->nr_thps);
-#else
-	WARN_ON_ONCE(mapping_large_folio_support(mapping) == 0);
-#endif
-}
-
-static inline void filemap_nr_thps_dec(struct address_space *mapping)
-{
-#ifdef CONFIG_READ_ONLY_THP_FOR_FS
-	if (!mapping_large_folio_support(mapping))
-		atomic_dec(&mapping->nr_thps);
-#else
-	WARN_ON_ONCE(mapping_large_folio_support(mapping) == 0);
-#endif
-}
-
 struct address_space *folio_mapping(const struct folio *folio);
 
 /**
diff --git a/mm/filemap.c b/mm/filemap.c
index 2b933a1da9bd..4248e7cdecf3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -189,7 +189,6 @@ static void filemap_unaccount_folio(struct address_space *mapping,
 			lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, -nr);
 	} else if (folio_test_pmd_mappable(folio)) {
 		lruvec_stat_mod_folio(folio, NR_FILE_THPS, -nr);
-		filemap_nr_thps_dec(mapping);
 	}
 	if (test_bit(AS_KERNEL_FILE, &folio->mapping->flags))
 		mod_node_page_state(folio_pgdat(folio),
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 610a6184e92c..54b3d21e4cbb 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3832,7 +3832,6 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
 				} else {
 					lruvec_stat_mod_folio(folio,
 							NR_FILE_THPS, -nr);
-					filemap_nr_thps_dec(mapping);
 				}
 			}
 		}
-- 
2.43.0

[RFC PATCH 04/11] mm/huge_memory: remove file_thp_enabled() and its caller.

[Zi Yan]

It is used by no-long-exist READ_ONLY_THP_FOR_FS.

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

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 54b3d21e4cbb..de4a1e6ce376 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -85,24 +85,6 @@ unsigned long huge_anon_orders_madvise __read_mostly;
 unsigned long huge_anon_orders_inherit __read_mostly;
 static bool anon_orders_configured __initdata;
 
-static inline bool file_thp_enabled(struct vm_area_struct *vma)
-{
-	struct inode *inode;
-
-	if (!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS))
-		return false;
-
-	if (!vma->vm_file)
-		return false;
-
-	inode = file_inode(vma->vm_file);
-
-	if (IS_ANON_FILE(inode))
-		return false;
-
-	return !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
-}
-
 /* If returns true, we are unable to access the VMA's folios. */
 static bool vma_is_special_huge(const struct vm_area_struct *vma)
 {
@@ -199,9 +181,6 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 		 */
 		if (((in_pf || smaps)) && vma->vm_ops->huge_fault)
 			return orders;
-		/* Only regular file is valid in collapse path */
-		if (((!in_pf || smaps)) && file_thp_enabled(vma))
-			return orders;
 		return 0;
 	}
 
-- 
2.43.0

[RFC PATCH 05/11] mm/huge_memory: remove folio split check for READ_ONLY_THP_FOR_FS

[Zi Yan]

Without READ_ONLY_THP_FOR_FS, large file-backed folios cannot be created by
a FS without large folio support. The check is no longer needed.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/huge_memory.c | 22 ----------------------
 1 file changed, 22 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index de4a1e6ce376..c7680787409c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3710,28 +3710,6 @@ int folio_check_splittable(struct folio *folio, unsigned int new_order,
 		/* order-1 is not supported for anonymous THP. */
 		if (new_order == 1)
 			return -EINVAL;
-	} else if (split_type == SPLIT_TYPE_NON_UNIFORM || new_order) {
-		if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
-		    !mapping_large_folio_support(folio->mapping)) {
-			/*
-			 * We can always split a folio down to a single page
-			 * (new_order == 0) uniformly.
-			 *
-			 * For any other scenario
-			 *   a) uniform split targeting a large folio
-			 *      (new_order > 0)
-			 *   b) any non-uniform split
-			 * we must confirm that the file system supports large
-			 * folios.
-			 *
-			 * Note that we might still have THPs in such
-			 * mappings, which is created from khugepaged when
-			 * CONFIG_READ_ONLY_THP_FOR_FS is enabled. But in that
-			 * case, the mapping does not actually support large
-			 * folios properly.
-			 */
-			return -EINVAL;
-		}
 	}
 
 	/*
-- 
2.43.0

[RFC PATCH 06/11] mm/truncate: use folio_split() in truncate_inode_partial_folio()

[Zi Yan]

After READ_ONLY_THP_FOR_FS is removed, FS either supports large folio or
not. folio_split() can be used on a FS with large folio support without
worrying about getting a THP on a FS without large folio support.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/huge_mm.h | 28 ----------------------------
 mm/truncate.c           |  8 ++++----
 2 files changed, 4 insertions(+), 32 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 1258fa37e85b..77c8f73f8839 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -389,27 +389,6 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o
 	return split_huge_page_to_list_to_order(page, NULL, new_order);
 }
 
-/**
- * try_folio_split_to_order() - try to split a @folio at @page to @new_order
- * using non uniform split.
- * @folio: folio to be split
- * @page: split to @new_order at the given page
- * @new_order: the target split order
- *
- * Try to split a @folio at @page using non uniform split to @new_order, if
- * non uniform split is not supported, fall back to uniform split. After-split
- * folios are put back to LRU list. Use min_order_for_split() to get the lower
- * bound of @new_order.
- *
- * Return: 0 - split is successful, otherwise split failed.
- */
-static inline int try_folio_split_to_order(struct folio *folio,
-		struct page *page, unsigned int new_order)
-{
-	if (folio_check_splittable(folio, new_order, SPLIT_TYPE_NON_UNIFORM))
-		return split_huge_page_to_order(&folio->page, new_order);
-	return folio_split(folio, new_order, page, NULL);
-}
 static inline int split_huge_page(struct page *page)
 {
 	return split_huge_page_to_list_to_order(page, NULL, 0);
@@ -641,13 +620,6 @@ static inline int split_folio_to_list(struct folio *folio, struct list_head *lis
 	return -EINVAL;
 }
 
-static inline int try_folio_split_to_order(struct folio *folio,
-		struct page *page, unsigned int new_order)
-{
-	VM_WARN_ON_ONCE_FOLIO(1, folio);
-	return -EINVAL;
-}
-
 static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {}
 #define split_huge_pmd(__vma, __pmd, __address)	\
 	do { } while (0)
diff --git a/mm/truncate.c b/mm/truncate.c
index 2931d66c16d0..6973b05ec4b8 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -177,7 +177,7 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio)
 	return 0;
 }
 
-static int try_folio_split_or_unmap(struct folio *folio, struct page *split_at,
+static int folio_split_or_unmap(struct folio *folio, struct page *split_at,
 				    unsigned long min_order)
 {
 	enum ttu_flags ttu_flags =
@@ -186,7 +186,7 @@ static int try_folio_split_or_unmap(struct folio *folio, struct page *split_at,
 		TTU_IGNORE_MLOCK;
 	int ret;
 
-	ret = try_folio_split_to_order(folio, split_at, min_order);
+	ret = folio_split(folio, min_order, split_at, NULL);
 
 	/*
 	 * If the split fails, unmap the folio, so it will be refaulted
@@ -252,7 +252,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
 
 	min_order = mapping_min_folio_order(folio->mapping);
 	split_at = folio_page(folio, PAGE_ALIGN_DOWN(offset) / PAGE_SIZE);
-	if (!try_folio_split_or_unmap(folio, split_at, min_order)) {
+	if (!folio_split_or_unmap(folio, split_at, min_order)) {
 		/*
 		 * try to split at offset + length to make sure folios within
 		 * the range can be dropped, especially to avoid memory waste
@@ -279,7 +279,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
 		/* make sure folio2 is large and does not change its mapping */
 		if (folio_test_large(folio2) &&
 		    folio2->mapping == folio->mapping)
-			try_folio_split_or_unmap(folio2, split_at2, min_order);
+			folio_split_or_unmap(folio2, split_at2, min_order);
 
 		folio_unlock(folio2);
 out:
-- 
2.43.0

[RFC PATCH 07/11] fs: remove nr_thp from struct address_space

[Zi Yan]

READ_ONLY_THP_FOR_FS is removed, the related field is no longer needed.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 fs/inode.c         | 3 ---
 include/linux/fs.h | 5 -----
 2 files changed, 8 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index cc12b68e021b..16ab0a345419 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -280,9 +280,6 @@ int inode_init_always_gfp(struct super_block *sb, struct inode *inode, gfp_t gfp
 	mapping->flags = 0;
 	mapping->wb_err = 0;
 	atomic_set(&mapping->i_mmap_writable, 0);
-#ifdef CONFIG_READ_ONLY_THP_FOR_FS
-	atomic_set(&mapping->nr_thps, 0);
-#endif
 	mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
 	mapping->i_private_data = NULL;
 	mapping->writeback_index = 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0bdccfa70b44..35875696fb4c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -455,7 +455,6 @@ extern const struct address_space_operations empty_aops;
  *   memory mappings.
  * @gfp_mask: Memory allocation flags to use for allocating pages.
  * @i_mmap_writable: Number of VM_SHARED, VM_MAYWRITE mappings.
- * @nr_thps: Number of THPs in the pagecache (non-shmem only).
  * @i_mmap: Tree of private and shared mappings.
  * @i_mmap_rwsem: Protects @i_mmap and @i_mmap_writable.
  * @nrpages: Number of page entries, protected by the i_pages lock.
@@ -473,10 +472,6 @@ struct address_space {
 	struct rw_semaphore	invalidate_lock;
 	gfp_t			gfp_mask;
 	atomic_t		i_mmap_writable;
-#ifdef CONFIG_READ_ONLY_THP_FOR_FS
-	/* number of thp, only for non-shmem files */
-	atomic_t		nr_thps;
-#endif
 	struct rb_root_cached	i_mmap;
 	unsigned long		nrpages;
 	pgoff_t			writeback_index;
-- 
2.43.0

[RFC PATCH 08/11] fs: remove READ_ONLY_THP_FOR_FS code

[Zi Yan]

READ_ONLY_THP_FOR_FS is no longer present, delete related code.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 fs/open.c | 27 ---------------------------
 1 file changed, 27 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 91f1139591ab..cef382d9d8b8 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -970,33 +970,6 @@ static int do_dentry_open(struct file *f,
 	if ((f->f_flags & O_DIRECT) && !(f->f_mode & FMODE_CAN_ODIRECT))
 		return -EINVAL;
 
-	/*
-	 * XXX: Huge page cache doesn't support writing yet. Drop all page
-	 * cache for this file before processing writes.
-	 */
-	if (f->f_mode & FMODE_WRITE) {
-		/*
-		 * Depends on full fence from get_write_access() to synchronize
-		 * against collapse_file() regarding i_writecount and nr_thps
-		 * updates. Ensures subsequent insertion of THPs into the page
-		 * cache will fail.
-		 */
-		if (filemap_nr_thps(inode->i_mapping)) {
-			struct address_space *mapping = inode->i_mapping;
-
-			filemap_invalidate_lock(inode->i_mapping);
-			/*
-			 * unmap_mapping_range just need to be called once
-			 * here, because the private pages is not need to be
-			 * unmapped mapping (e.g. data segment of dynamic
-			 * shared libraries here).
-			 */
-			unmap_mapping_range(mapping, 0, 0, 0);
-			truncate_inode_pages(mapping, 0);
-			filemap_invalidate_unlock(inode->i_mapping);
-		}
-	}
-
 	return 0;
 
 cleanup_all:
-- 
2.43.0

[RFC PATCH 09/11] fs/btrfs: remove a comment referring to READ_ONLY_THP_FOR_FS

[Zi Yan]

READ_ONLY_THP_FOR_FS is no longer present, remove related comment.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 fs/btrfs/defrag.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/fs/btrfs/defrag.c b/fs/btrfs/defrag.c
index 7e2db5d3a4d4..a8d49d9ca981 100644
--- a/fs/btrfs/defrag.c
+++ b/fs/btrfs/defrag.c
@@ -860,9 +860,6 @@ static struct folio *defrag_prepare_one_folio(struct btrfs_inode *inode, pgoff_t
 		return folio;
 
 	/*
-	 * Since we can defragment files opened read-only, we can encounter
-	 * transparent huge pages here (see CONFIG_READ_ONLY_THP_FOR_FS).
-	 *
 	 * The IO for such large folios is not fully tested, thus return
 	 * an error to reject such folios unless it's an experimental build.
 	 *
-- 
2.43.0

[RFC PATCH 10/11] selftests/mm: remove READ_ONLY_THP_FOR_FS test in khugepaged

[Zi Yan]

READ_ONLY_THP_FOR_FS is no longer present, remove related test.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 tools/testing/selftests/mm/khugepaged.c | 197 +-----------------------
 1 file changed, 3 insertions(+), 194 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 3fe7ef04ac62..842311682833 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -37,7 +37,6 @@ static int anon_order;
 
 enum vma_type {
 	VMA_ANON,
-	VMA_FILE,
 	VMA_SHMEM,
 };
 
@@ -49,7 +48,6 @@ struct mem_ops {
 	const char *name;
 };
 
-static struct mem_ops *file_ops;
 static struct mem_ops *anon_ops;
 static struct mem_ops *shmem_ops;
 
@@ -112,8 +110,6 @@ static void restore_settings(int sig)
 static void save_settings(void)
 {
 	printf("Save THP and khugepaged settings...");
-	if (file_ops && finfo.type == VMA_FILE)
-		thp_set_read_ahead_path(finfo.dev_queue_read_ahead_path);
 	thp_save_settings();
 
 	success("OK");
@@ -125,89 +121,6 @@ static void save_settings(void)
 	signal(SIGQUIT, restore_settings);
 }
 
-static void get_finfo(const char *dir)
-{
-	struct stat path_stat;
-	struct statfs fs;
-	char buf[1 << 10];
-	char path[PATH_MAX];
-	char *str, *end;
-
-	finfo.dir = dir;
-	stat(finfo.dir, &path_stat);
-	if (!S_ISDIR(path_stat.st_mode)) {
-		printf("%s: Not a directory (%s)\n", __func__, finfo.dir);
-		exit(EXIT_FAILURE);
-	}
-	if (snprintf(finfo.path, sizeof(finfo.path), "%s/" TEST_FILE,
-		     finfo.dir) >= sizeof(finfo.path)) {
-		printf("%s: Pathname is too long\n", __func__);
-		exit(EXIT_FAILURE);
-	}
-	if (statfs(finfo.dir, &fs)) {
-		perror("statfs()");
-		exit(EXIT_FAILURE);
-	}
-	finfo.type = fs.f_type == TMPFS_MAGIC ? VMA_SHMEM : VMA_FILE;
-	if (finfo.type == VMA_SHMEM)
-		return;
-
-	/* Find owning device's queue/read_ahead_kb control */
-	if (snprintf(path, sizeof(path), "/sys/dev/block/%d:%d/uevent",
-		     major(path_stat.st_dev), minor(path_stat.st_dev))
-	    >= sizeof(path)) {
-		printf("%s: Pathname is too long\n", __func__);
-		exit(EXIT_FAILURE);
-	}
-	if (read_file(path, buf, sizeof(buf)) < 0) {
-		perror("read_file(read_num)");
-		exit(EXIT_FAILURE);
-	}
-	if (strstr(buf, "DEVTYPE=disk")) {
-		/* Found it */
-		if (snprintf(finfo.dev_queue_read_ahead_path,
-			     sizeof(finfo.dev_queue_read_ahead_path),
-			     "/sys/dev/block/%d:%d/queue/read_ahead_kb",
-			     major(path_stat.st_dev), minor(path_stat.st_dev))
-		    >= sizeof(finfo.dev_queue_read_ahead_path)) {
-			printf("%s: Pathname is too long\n", __func__);
-			exit(EXIT_FAILURE);
-		}
-		return;
-	}
-	if (!strstr(buf, "DEVTYPE=partition")) {
-		printf("%s: Unknown device type: %s\n", __func__, path);
-		exit(EXIT_FAILURE);
-	}
-	/*
-	 * Partition of block device - need to find actual device.
-	 * Using naming convention that devnameN is partition of
-	 * device devname.
-	 */
-	str = strstr(buf, "DEVNAME=");
-	if (!str) {
-		printf("%s: Could not read: %s", __func__, path);
-		exit(EXIT_FAILURE);
-	}
-	str += 8;
-	end = str;
-	while (*end) {
-		if (isdigit(*end)) {
-			*end = '\0';
-			if (snprintf(finfo.dev_queue_read_ahead_path,
-				     sizeof(finfo.dev_queue_read_ahead_path),
-				     "/sys/block/%s/queue/read_ahead_kb",
-				     str) >= sizeof(finfo.dev_queue_read_ahead_path)) {
-				printf("%s: Pathname is too long\n", __func__);
-				exit(EXIT_FAILURE);
-			}
-			return;
-		}
-		++end;
-	}
-	printf("%s: Could not read: %s\n", __func__, path);
-	exit(EXIT_FAILURE);
-}
 
 static bool check_swap(void *addr, unsigned long size)
 {
@@ -364,77 +277,6 @@ static bool anon_check_huge(void *addr, int nr_hpages)
 	return check_huge_anon(addr, nr_hpages, hpage_pmd_size);
 }
 
-static void *file_setup_area(int nr_hpages)
-{
-	int fd;
-	void *p;
-	unsigned long size;
-
-	unlink(finfo.path);  /* Cleanup from previous failed tests */
-	printf("Creating %s for collapse%s...", finfo.path,
-	       finfo.type == VMA_SHMEM ? " (tmpfs)" : "");
-	fd = open(finfo.path, O_DSYNC | O_CREAT | O_RDWR | O_TRUNC | O_EXCL,
-		  777);
-	if (fd < 0) {
-		perror("open()");
-		exit(EXIT_FAILURE);
-	}
-
-	size = nr_hpages * hpage_pmd_size;
-	p = alloc_mapping(nr_hpages);
-	fill_memory(p, 0, size);
-	write(fd, p, size);
-	close(fd);
-	munmap(p, size);
-	success("OK");
-
-	printf("Opening %s read only for collapse...", finfo.path);
-	finfo.fd = open(finfo.path, O_RDONLY, 777);
-	if (finfo.fd < 0) {
-		perror("open()");
-		exit(EXIT_FAILURE);
-	}
-	p = mmap(BASE_ADDR, size, PROT_READ,
-		 MAP_PRIVATE, finfo.fd, 0);
-	if (p == MAP_FAILED || p != BASE_ADDR) {
-		perror("mmap()");
-		exit(EXIT_FAILURE);
-	}
-
-	/* Drop page cache */
-	write_file("/proc/sys/vm/drop_caches", "3", 2);
-	success("OK");
-	return p;
-}
-
-static void file_cleanup_area(void *p, unsigned long size)
-{
-	munmap(p, size);
-	close(finfo.fd);
-	unlink(finfo.path);
-}
-
-static void file_fault(void *p, unsigned long start, unsigned long end)
-{
-	if (madvise(((char *)p) + start, end - start, MADV_POPULATE_READ)) {
-		perror("madvise(MADV_POPULATE_READ");
-		exit(EXIT_FAILURE);
-	}
-}
-
-static bool file_check_huge(void *addr, int nr_hpages)
-{
-	switch (finfo.type) {
-	case VMA_FILE:
-		return check_huge_file(addr, nr_hpages, hpage_pmd_size);
-	case VMA_SHMEM:
-		return check_huge_shmem(addr, nr_hpages, hpage_pmd_size);
-	default:
-		exit(EXIT_FAILURE);
-		return false;
-	}
-}
-
 static void *shmem_setup_area(int nr_hpages)
 {
 	void *p;
@@ -477,14 +319,6 @@ static struct mem_ops __anon_ops = {
 	.name = "anon",
 };
 
-static struct mem_ops __file_ops = {
-	.setup_area = &file_setup_area,
-	.cleanup_area = &file_cleanup_area,
-	.fault = &file_fault,
-	.check_huge = &file_check_huge,
-	.name = "file",
-};
-
 static struct mem_ops __shmem_ops = {
 	.setup_area = &shmem_setup_area,
 	.cleanup_area = &shmem_cleanup_area,
@@ -576,7 +410,7 @@ static void khugepaged_collapse(const char *msg, char *p, int nr_hpages,
 	}
 
 	/*
-	 * For file and shmem memory, khugepaged only retracts pte entries after
+	 * For shmem memory, khugepaged only retracts pte entries after
 	 * putting the new hugepage in the page cache. The hugepage must be
 	 * subsequently refaulted to install the pmd mapping for the mm.
 	 */
@@ -603,7 +437,7 @@ static struct collapse_context __madvise_context = {
 
 static bool is_tmpfs(struct mem_ops *ops)
 {
-	return ops == &__file_ops && finfo.type == VMA_SHMEM;
+	return finfo.type == VMA_SHMEM;
 }
 
 static bool is_anon(struct mem_ops *ops)
@@ -1084,10 +918,7 @@ static void usage(void)
 	fprintf(stderr, "\nUsage: ./khugepaged [OPTIONS] <test type> [dir]\n\n");
 	fprintf(stderr, "\t<test type>\t: <context>:<mem_type>\n");
 	fprintf(stderr, "\t<context>\t: [all|khugepaged|madvise]\n");
-	fprintf(stderr, "\t<mem_type>\t: [all|anon|file|shmem]\n");
-	fprintf(stderr, "\n\t\"file,all\" mem_type requires [dir] argument\n");
-	fprintf(stderr, "\n\t\"file,all\" mem_type requires kernel built with\n");
-	fprintf(stderr,	"\tCONFIG_READ_ONLY_THP_FOR_FS=y\n");
+	fprintf(stderr, "\t<mem_type>\t: [all|anon|shmem]\n");
 	fprintf(stderr, "\n\tif [dir] is a (sub)directory of a tmpfs mount, tmpfs must be\n");
 	fprintf(stderr,	"\tmounted with huge=advise option for khugepaged tests to work\n");
 	fprintf(stderr,	"\n\tSupported Options:\n");
@@ -1143,26 +974,16 @@ static void parse_test_type(int argc, char **argv)
 		usage();
 
 	if (!strcmp(buf, "all")) {
-		file_ops =  &__file_ops;
 		anon_ops = &__anon_ops;
 		shmem_ops = &__shmem_ops;
 	} else if (!strcmp(buf, "anon")) {
 		anon_ops = &__anon_ops;
-	} else if (!strcmp(buf, "file")) {
-		file_ops =  &__file_ops;
 	} else if (!strcmp(buf, "shmem")) {
 		shmem_ops = &__shmem_ops;
 	} else {
 		usage();
 	}
 
-	if (!file_ops)
-		return;
-
-	if (argc != 2)
-		usage();
-
-	get_finfo(argv[1]);
 }
 
 int main(int argc, char **argv)
@@ -1228,37 +1049,27 @@ int main(int argc, char **argv)
 	} while (0)
 
 	TEST(collapse_full, khugepaged_context, anon_ops);
-	TEST(collapse_full, khugepaged_context, file_ops);
 	TEST(collapse_full, khugepaged_context, shmem_ops);
 	TEST(collapse_full, madvise_context, anon_ops);
-	TEST(collapse_full, madvise_context, file_ops);
 	TEST(collapse_full, madvise_context, shmem_ops);
 
 	TEST(collapse_empty, khugepaged_context, anon_ops);
 	TEST(collapse_empty, madvise_context, anon_ops);
 
 	TEST(collapse_single_pte_entry, khugepaged_context, anon_ops);
-	TEST(collapse_single_pte_entry, khugepaged_context, file_ops);
 	TEST(collapse_single_pte_entry, khugepaged_context, shmem_ops);
 	TEST(collapse_single_pte_entry, madvise_context, anon_ops);
-	TEST(collapse_single_pte_entry, madvise_context, file_ops);
 	TEST(collapse_single_pte_entry, madvise_context, shmem_ops);
 
 	TEST(collapse_max_ptes_none, khugepaged_context, anon_ops);
-	TEST(collapse_max_ptes_none, khugepaged_context, file_ops);
 	TEST(collapse_max_ptes_none, madvise_context, anon_ops);
-	TEST(collapse_max_ptes_none, madvise_context, file_ops);
 
 	TEST(collapse_single_pte_entry_compound, khugepaged_context, anon_ops);
-	TEST(collapse_single_pte_entry_compound, khugepaged_context, file_ops);
 	TEST(collapse_single_pte_entry_compound, madvise_context, anon_ops);
-	TEST(collapse_single_pte_entry_compound, madvise_context, file_ops);
 
 	TEST(collapse_full_of_compound, khugepaged_context, anon_ops);
-	TEST(collapse_full_of_compound, khugepaged_context, file_ops);
 	TEST(collapse_full_of_compound, khugepaged_context, shmem_ops);
 	TEST(collapse_full_of_compound, madvise_context, anon_ops);
-	TEST(collapse_full_of_compound, madvise_context, file_ops);
 	TEST(collapse_full_of_compound, madvise_context, shmem_ops);
 
 	TEST(collapse_compound_extreme, khugepaged_context, anon_ops);
@@ -1280,10 +1091,8 @@ int main(int argc, char **argv)
 	TEST(collapse_max_ptes_shared, madvise_context, anon_ops);
 
 	TEST(madvise_collapse_existing_thps, madvise_context, anon_ops);
-	TEST(madvise_collapse_existing_thps, madvise_context, file_ops);
 	TEST(madvise_collapse_existing_thps, madvise_context, shmem_ops);
 
-	TEST(madvise_retracted_page_tables, madvise_context, file_ops);
 	TEST(madvise_retracted_page_tables, madvise_context, shmem_ops);
 
 	restore_settings(0);
-- 
2.43.0

[RFC PATCH 11/11] selftests/mm: remove READ_ONLY_THP_FOR_FS test in guard-regions

[Zi Yan]

READ_ONLY_THP_FOR_FS is no longer present, remove related test.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 tools/testing/selftests/mm/guard-regions.c | 148 +--------------------
 1 file changed, 1 insertion(+), 147 deletions(-)

diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c
index 48e8b1539be3..fc8b2a4e7ba2 100644
--- a/tools/testing/selftests/mm/guard-regions.c
+++ b/tools/testing/selftests/mm/guard-regions.c
@@ -42,7 +42,6 @@ static sigjmp_buf signal_jmp_buf;
 enum backing_type {
 	ANON_BACKED,
 	SHMEM_BACKED,
-	LOCAL_FILE_BACKED,
 };
 
 FIXTURE(guard_regions)
@@ -67,11 +66,6 @@ FIXTURE_VARIANT_ADD(guard_regions, shmem)
 	.backing = SHMEM_BACKED,
 };
 
-FIXTURE_VARIANT_ADD(guard_regions, file)
-{
-	.backing = LOCAL_FILE_BACKED,
-};
-
 static bool is_anon_backed(const FIXTURE_VARIANT(guard_regions) * variant)
 {
 	switch (variant->backing) {
@@ -98,7 +92,6 @@ static void *mmap_(FIXTURE_DATA(guard_regions) * self,
 		offset = 0;
 		break;
 	case SHMEM_BACKED:
-	case LOCAL_FILE_BACKED:
 		flags |= MAP_SHARED;
 		fd = self->fd;
 		break;
@@ -198,18 +191,6 @@ static void teardown_sighandler(void)
 	sigaction(SIGSEGV, &act, NULL);
 }
 
-static int open_file(const char *prefix, char *path)
-{
-	int fd;
-
-	snprintf(path, PATH_MAX, "%sguard_regions_test_file_XXXXXX", prefix);
-	fd = mkstemp(path);
-	if (fd < 0)
-		ksft_exit_fail_perror("mkstemp");
-
-	return fd;
-}
-
 /* Establish a varying pattern in a buffer. */
 static void set_pattern(char *ptr, size_t num_pages, size_t page_size)
 {
@@ -262,54 +243,6 @@ static bool is_buf_eq(char *buf, size_t size, char chr)
 	return true;
 }
 
-/*
- * Some file systems have issues with merging due to changing merge-sensitive
- * parameters in the .mmap callback, and prior to .mmap_prepare being
- * implemented everywhere this will now result in an unexpected failure to
- * merge (e.g. - overlayfs).
- *
- * Perform a simple test to see if the local file system suffers from this, if
- * it does then we can skip test logic that assumes local file system merging is
- * sane.
- */
-static bool local_fs_has_sane_mmap(FIXTURE_DATA(guard_regions) * self,
-				   const FIXTURE_VARIANT(guard_regions) * variant)
-{
-	const unsigned long page_size = self->page_size;
-	char *ptr, *ptr2;
-	struct procmap_fd procmap;
-
-	if (variant->backing != LOCAL_FILE_BACKED)
-		return true;
-
-	/* Map 10 pages. */
-	ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PROT_WRITE, 0, 0);
-	if (ptr == MAP_FAILED)
-		return false;
-	/* Unmap the middle. */
-	munmap(&ptr[5 * page_size], page_size);
-
-	/* Map again. */
-	ptr2 = mmap_(self, variant, &ptr[5 * page_size], page_size, PROT_READ | PROT_WRITE,
-		     MAP_FIXED, 5 * page_size);
-
-	if (ptr2 == MAP_FAILED)
-		return false;
-
-	/* Now make sure they all merged. */
-	if (open_self_procmap(&procmap) != 0)
-		return false;
-	if (!find_vma_procmap(&procmap, ptr))
-		return false;
-	if (procmap.query.vma_start != (unsigned long)ptr)
-		return false;
-	if (procmap.query.vma_end != (unsigned long)ptr + 10 * page_size)
-		return false;
-	close_procmap(&procmap);
-
-	return true;
-}
-
 FIXTURE_SETUP(guard_regions)
 {
 	self->page_size = (unsigned long)sysconf(_SC_PAGESIZE);
@@ -318,9 +251,6 @@ FIXTURE_SETUP(guard_regions)
 	switch (variant->backing) {
 	case ANON_BACKED:
 		return;
-	case LOCAL_FILE_BACKED:
-		self->fd = open_file("", self->path);
-		break;
 	case SHMEM_BACKED:
 		self->fd = memfd_create(self->path, 0);
 		break;
@@ -1750,55 +1680,6 @@ TEST_F(guard_regions, map_private)
 	ASSERT_EQ(munmap(ptr_private, 10 * page_size), 0);
 }
 
-/* Test that guard regions established over a read-only mapping function correctly. */
-TEST_F(guard_regions, readonly_file)
-{
-	const unsigned long page_size = self->page_size;
-	char *ptr;
-	int i;
-
-	if (variant->backing != LOCAL_FILE_BACKED)
-		SKIP(return, "Read-only test specific to file-backed");
-
-	/* Map shared so we can populate with pattern, populate it, unmap. */
-	ptr = mmap_(self, variant, NULL, 10 * page_size,
-		    PROT_READ | PROT_WRITE, 0, 0);
-	ASSERT_NE(ptr, MAP_FAILED);
-	set_pattern(ptr, 10, page_size);
-	ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
-	/* Close the fd so we can re-open read-only. */
-	ASSERT_EQ(close(self->fd), 0);
-
-	/* Re-open read-only. */
-	self->fd = open(self->path, O_RDONLY);
-	ASSERT_NE(self->fd, -1);
-	/* Re-map read-only. */
-	ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ, 0, 0);
-	ASSERT_NE(ptr, MAP_FAILED);
-
-	/* Mark every other page guarded. */
-	for (i = 0; i < 10; i += 2) {
-		char *ptr_pg = &ptr[i * page_size];
-
-		ASSERT_EQ(madvise(ptr_pg, page_size, MADV_GUARD_INSTALL), 0);
-	}
-
-	/* Assert that the guard regions are in place.*/
-	for (i = 0; i < 10; i++) {
-		char *ptr_pg = &ptr[i * page_size];
-
-		ASSERT_EQ(try_read_buf(ptr_pg), i % 2 != 0);
-	}
-
-	/* Remove guard regions. */
-	ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0);
-
-	/* Ensure the data is as expected. */
-	ASSERT_TRUE(check_pattern(ptr, 10, page_size));
-
-	ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
-}
-
 TEST_F(guard_regions, fault_around)
 {
 	const unsigned long page_size = self->page_size;
@@ -2203,17 +2084,6 @@ TEST_F(guard_regions, collapse)
 	if (variant->backing != ANON_BACKED)
 		ASSERT_EQ(ftruncate(self->fd, size), 0);
 
-	/*
-	 * We must close and re-open local-file backed as read-only for
-	 * CONFIG_READ_ONLY_THP_FOR_FS to work.
-	 */
-	if (variant->backing == LOCAL_FILE_BACKED) {
-		ASSERT_EQ(close(self->fd), 0);
-
-		self->fd = open(self->path, O_RDONLY);
-		ASSERT_GE(self->fd, 0);
-	}
-
 	ptr = mmap_(self, variant, NULL, size, PROT_READ, 0, 0);
 	ASSERT_NE(ptr, MAP_FAILED);
 
@@ -2234,13 +2104,7 @@ TEST_F(guard_regions, collapse)
 	/* Allow huge page throughout region. */
 	ASSERT_EQ(madvise(ptr, size, MADV_HUGEPAGE), 0);
 
-	/*
-	 * Now collapse the entire region. This should fail in all cases.
-	 *
-	 * The madvise() call will also fail if CONFIG_READ_ONLY_THP_FOR_FS is
-	 * not set for the local file case, but we can't differentiate whether
-	 * this occurred or if the collapse was rightly rejected.
-	 */
+	/* Now collapse the entire region. This should fail in all cases. */
 	EXPECT_NE(madvise(ptr, size, MADV_COLLAPSE), 0);
 
 	/*
@@ -2298,16 +2162,6 @@ TEST_F(guard_regions, smaps)
 	ASSERT_TRUE(check_vmflag_guard(ptr));
 	ASSERT_TRUE(check_vmflag_guard(&ptr[5 * page_size]));
 
-	/*
-	 * If the local file system is unable to merge VMAs due to having
-	 * unusual characteristics, there is no point in asserting merge
-	 * behaviour.
-	 */
-	if (!local_fs_has_sane_mmap(self, variant)) {
-		TH_LOG("local filesystem does not support sane merging skipping merge test");
-		return;
-	}
-
 	/* Map a fresh VMA between the two split VMAs. */
 	ptr2 = mmap_(self, variant, &ptr[4 * page_size], page_size,
 		     PROT_READ | PROT_WRITE, MAP_FIXED, 4 * page_size);
-- 
2.43.0

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[David Hildenbrand (Arm)]

On 3/23/26 20:06, Zi Yan wrote:
> READ_ONLY_THP_FOR_FS is no longer present, remove corresponding code.
> 
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
>  mm/khugepaged.c | 159 +++++++++++-------------------------------------
>  1 file changed, 34 insertions(+), 125 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b2ac28ddd480..39f0b8959535 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1899,7 +1899,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
>  	int nr_none = 0;
>  	bool is_shmem = shmem_file(file);
>  
> -	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
> +	VM_WARN_ON_ONCE(!is_shmem);

Oh, but if that means that khugepaged cannot collapse large folios in
FSes anymore, then this is the wrong approach I suppose?

I would have assumed that we would now collapse for any files that
support large folios (in PMD size), not stopping to collapse entirely.

-- 
Cheers,

David

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Zi Yan]

On 23 Mar 2026, at 15:41, David Hildenbrand (Arm) wrote:

> On 3/23/26 20:06, Zi Yan wrote:
>> READ_ONLY_THP_FOR_FS is no longer present, remove corresponding code.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>>  mm/khugepaged.c | 159 +++++++++++-------------------------------------
>>  1 file changed, 34 insertions(+), 125 deletions(-)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index b2ac28ddd480..39f0b8959535 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -1899,7 +1899,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
>>  	int nr_none = 0;
>>  	bool is_shmem = shmem_file(file);
>>
>> -	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
>> +	VM_WARN_ON_ONCE(!is_shmem);
>
> Oh, but if that means that khugepaged cannot collapse large folios in
> FSes anymore, then this is the wrong approach I suppose?
>
> I would have assumed that we would now collapse for any files that
> support large folios (in PMD size), not stopping to collapse entirely.

My understanding is that collapse_file() is only used for
READ_ONLY_THP_FOR_FS. If FSes with large folio support also use it,
I can replace IS_ENABLE with mapping_large_folio_support().

Best Regards,
Yan, Zi

Re: [RFC PATCH 09/11] fs/btrfs: remove a comment referring to READ_ONLY_THP_FOR_FS

[David Sterba]

On Mon, Mar 23, 2026 at 03:06:42PM -0400, Zi Yan wrote:
> READ_ONLY_THP_FOR_FS is no longer present, remove related comment.
> 
> Signed-off-by: Zi Yan <ziy@nvidia.com>

Acked-by: David Sterba <dsterba@suse.com>

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[David Hildenbrand (Arm)]

On 3/23/26 20:47, Zi Yan wrote:
> On 23 Mar 2026, at 15:41, David Hildenbrand (Arm) wrote:
> 
>> On 3/23/26 20:06, Zi Yan wrote:
>>> READ_ONLY_THP_FOR_FS is no longer present, remove corresponding code.
>>>
>>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>>> ---
>>>  mm/khugepaged.c | 159 +++++++++++-------------------------------------
>>>  1 file changed, 34 insertions(+), 125 deletions(-)
>>>
>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>>> index b2ac28ddd480..39f0b8959535 100644
>>> --- a/mm/khugepaged.c
>>> +++ b/mm/khugepaged.c
>>> @@ -1899,7 +1899,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
>>>  	int nr_none = 0;
>>>  	bool is_shmem = shmem_file(file);
>>>
>>> -	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
>>> +	VM_WARN_ON_ONCE(!is_shmem);
>>
>> Oh, but if that means that khugepaged cannot collapse large folios in
>> FSes anymore, then this is the wrong approach I suppose?
>>
>> I would have assumed that we would now collapse for any files that
>> support large folios (in PMD size), not stopping to collapse entirely.
> 
> My understanding is that collapse_file() is only used for
> READ_ONLY_THP_FOR_FS. If FSes with large folio support also use it,
> I can replace IS_ENABLE with mapping_large_folio_support().

Otherwise we'd be losing support for THP collapse in files? We'd have to
cross fingers that readahead gives us some.

So we have to be a bit careful here. We want khugepaged to collapse THPs
in filesystems that support large folios even without READ_ONLY_THP_FOR_FS.

-- 
Cheers,

David

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Zi Yan]

On 23 Mar 2026, at 15:53, David Hildenbrand (Arm) wrote:

> On 3/23/26 20:47, Zi Yan wrote:
>> On 23 Mar 2026, at 15:41, David Hildenbrand (Arm) wrote:
>>
>>> On 3/23/26 20:06, Zi Yan wrote:
>>>> READ_ONLY_THP_FOR_FS is no longer present, remove corresponding code.
>>>>
>>>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>>>> ---
>>>>  mm/khugepaged.c | 159 +++++++++++-------------------------------------
>>>>  1 file changed, 34 insertions(+), 125 deletions(-)
>>>>
>>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>>>> index b2ac28ddd480..39f0b8959535 100644
>>>> --- a/mm/khugepaged.c
>>>> +++ b/mm/khugepaged.c
>>>> @@ -1899,7 +1899,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
>>>>  	int nr_none = 0;
>>>>  	bool is_shmem = shmem_file(file);
>>>>
>>>> -	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
>>>> +	VM_WARN_ON_ONCE(!is_shmem);
>>>
>>> Oh, but if that means that khugepaged cannot collapse large folios in
>>> FSes anymore, then this is the wrong approach I suppose?
>>>
>>> I would have assumed that we would now collapse for any files that
>>> support large folios (in PMD size), not stopping to collapse entirely.
>>
>> My understanding is that collapse_file() is only used for
>> READ_ONLY_THP_FOR_FS. If FSes with large folio support also use it,
>> I can replace IS_ENABLE with mapping_large_folio_support().
>
> Otherwise we'd be losing support for THP collapse in files? We'd have to
> cross fingers that readahead gives us some.
>
> So we have to be a bit careful here. We want khugepaged to collapse THPs
> in filesystems that support large folios even without READ_ONLY_THP_FOR_FS.

Based on[1], collapse_file() only works on read-only fd. So it is not
as general as all files. If we do what you suggested, the function
will be collapse read-only folios from FSes with large folio support.

BTW, has anyone used/relied on collapse_file() on any FS with large folio
support?

[1] https://elixir.bootlin.com/linux/v6.19.9/source/mm/khugepaged.c#L1956


Best Regards,
Yan, Zi

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[David Hildenbrand (Arm)]

On 3/23/26 20:59, Zi Yan wrote:
> On 23 Mar 2026, at 15:53, David Hildenbrand (Arm) wrote:
> 
>> On 3/23/26 20:47, Zi Yan wrote:
>>>
>>>
>>> My understanding is that collapse_file() is only used for
>>> READ_ONLY_THP_FOR_FS. If FSes with large folio support also use it,
>>> I can replace IS_ENABLE with mapping_large_folio_support().
>>
>> Otherwise we'd be losing support for THP collapse in files? We'd have to
>> cross fingers that readahead gives us some.
>>
>> So we have to be a bit careful here. We want khugepaged to collapse THPs
>> in filesystems that support large folios even without READ_ONLY_THP_FOR_FS.
> 
> Based on[1], collapse_file() only works on read-only fd. So it is not
> as general as all files. If we do what you suggested, the function
> will be collapse read-only folios from FSes with large folio support.

Right, I think that's the first step to keep the existing use case
working. Long term, I suspect we might want to extend that to writable
files etc.

> 
> BTW, has anyone used/relied on collapse_file() on any FS with large folio
> support?

I assume so, because for executables you would have to be lucky to get a
PMD THP? So I don't see the non-khugepaged large folio support on par
with khugepaged support.

-- 
Cheers,

David

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Zi Yan]

On 23 Mar 2026, at 16:13, David Hildenbrand (Arm) wrote:

> On 3/23/26 20:59, Zi Yan wrote:
>> On 23 Mar 2026, at 15:53, David Hildenbrand (Arm) wrote:
>>
>>> On 3/23/26 20:47, Zi Yan wrote:
>>>>
>>>>
>>>> My understanding is that collapse_file() is only used for
>>>> READ_ONLY_THP_FOR_FS. If FSes with large folio support also use it,
>>>> I can replace IS_ENABLE with mapping_large_folio_support().
>>>
>>> Otherwise we'd be losing support for THP collapse in files? We'd have to
>>> cross fingers that readahead gives us some.
>>>
>>> So we have to be a bit careful here. We want khugepaged to collapse THPs
>>> in filesystems that support large folios even without READ_ONLY_THP_FOR_FS.
>>
>> Based on[1], collapse_file() only works on read-only fd. So it is not
>> as general as all files. If we do what you suggested, the function
>> will be collapse read-only folios from FSes with large folio support.
>
> Right, I think that's the first step to keep the existing use case
> working. Long term, I suspect we might want to extend that to writable
> files etc.
>
>>
>> BTW, has anyone used/relied on collapse_file() on any FS with large folio
>> support?
>
> I assume so, because for executables you would have to be lucky to get a
> PMD THP? So I don't see the non-khugepaged large folio support on par
> with khugepaged support.

It is more like turning on READ_ONLY_THP_FOR_FS by default for
FS with large folio support instead of removing it.

OK, I will give it another try.


Best Regards,
Yan, Zi

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Matthew Wilcox]

On Mon, Mar 23, 2026 at 04:24:26PM -0400, Zi Yan wrote:
> On 23 Mar 2026, at 16:13, David Hildenbrand (Arm) wrote:
> > I assume so, because for executables you would have to be lucky to get a
> > PMD THP? So I don't see the non-khugepaged large folio support on par
> > with khugepaged support.

Not necessarily that lucky; if you set VM_HUGEPAGE,
do_sync_mmap_readahead() will allocate PMD-sized folios automatically.
On busy database servers (and is there any other kind?), khugepaged
takes too long to run and find opportunities to collapse text pages.
Like, days.

> It is more like turning on READ_ONLY_THP_FOR_FS by default for
> FS with large folio support instead of removing it.
> 
> OK, I will give it another try.

I think the test needs to be:

	if (mapping_max_folio_order(mapping) >= PMD_ORDER)

as there can be cases of filesystems which support up to, say, 64KiB,
but not all the way up to 2MiB.  I disapprove of this situation, but
this is where we are right now.

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[David Hildenbrand (Arm)]

On 3/23/26 22:02, Matthew Wilcox wrote:
> On Mon, Mar 23, 2026 at 04:24:26PM -0400, Zi Yan wrote:
>> On 23 Mar 2026, at 16:13, David Hildenbrand (Arm) wrote:
>>> I assume so, because for executables you would have to be lucky to get a
>>> PMD THP? So I don't see the non-khugepaged large folio support on par
>>> with khugepaged support.
> 
> Not necessarily that lucky; if you set VM_HUGEPAGE,
> do_sync_mmap_readahead() will allocate PMD-sized folios automatically.
> On busy database servers (and is there any other kind?), khugepaged
> takes too long to run and find opportunities to collapse text pages.
> Like, days.

Yes, in particular given that the default khugepaged settings are awful.

> 
>> It is more like turning on READ_ONLY_THP_FOR_FS by default for
>> FS with large folio support instead of removing it.
>>
>> OK, I will give it another try.
> 
> I think the test needs to be:
> 
> 	if (mapping_max_folio_order(mapping) >= PMD_ORDER)
> 
> as there can be cases of filesystems which support up to, say, 64KiB,
> but not all the way up to 2MiB.  I disapprove of this situation, but
> this is where we are right now.

Right, that's what I had in mind.

-- 
Cheers,

David

Re: [RFC PATCH 10/11] selftests/mm: remove READ_ONLY_THP_FOR_FS test in khugepaged

[Matthew Wilcox]

On Mon, Mar 23, 2026 at 03:06:43PM -0400, Zi Yan wrote:
> READ_ONLY_THP_FOR_FS is no longer present, remove related test.

Um, surely we want to keep the test?  It's no longer conditional on
READ_ONLY_THP_FOR_FS being enabled, but we still want to collapse
mapped files.

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Zi Yan]

On 23 Mar 2026, at 17:05, David Hildenbrand (Arm) wrote:

> On 3/23/26 22:02, Matthew Wilcox wrote:
>> On Mon, Mar 23, 2026 at 04:24:26PM -0400, Zi Yan wrote:
>>> On 23 Mar 2026, at 16:13, David Hildenbrand (Arm) wrote:
>>>> I assume so, because for executables you would have to be lucky to get a
>>>> PMD THP? So I don't see the non-khugepaged large folio support on par
>>>> with khugepaged support.
>>
>> Not necessarily that lucky; if you set VM_HUGEPAGE,
>> do_sync_mmap_readahead() will allocate PMD-sized folios automatically.
>> On busy database servers (and is there any other kind?), khugepaged
>> takes too long to run and find opportunities to collapse text pages.
>> Like, days.
>
> Yes, in particular given that the default khugepaged settings are awful.
>
>>
>>> It is more like turning on READ_ONLY_THP_FOR_FS by default for
>>> FS with large folio support instead of removing it.
>>>
>>> OK, I will give it another try.
>>
>> I think the test needs to be:
>>
>> 	if (mapping_max_folio_order(mapping) >= PMD_ORDER)

This is very helpful, since I was thinking about using
mapping_large_folio_support().

>>
>> as there can be cases of filesystems which support up to, say, 64KiB,
>> but not all the way up to 2MiB.  I disapprove of this situation, but
>> this is where we are right now.
>
> Right, that's what I had in mind.

Does Nico’s mTHP support for khugepaged include changes to collapse_file()?
That might change the above test.

Best Regards,
Yan, Zi

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[David Hildenbrand (Arm)]

On 3/23/26 22:11, Zi Yan wrote:
> On 23 Mar 2026, at 17:05, David Hildenbrand (Arm) wrote:
> 
>> On 3/23/26 22:02, Matthew Wilcox wrote:
>>>
>>> Not necessarily that lucky; if you set VM_HUGEPAGE,
>>> do_sync_mmap_readahead() will allocate PMD-sized folios automatically.
>>> On busy database servers (and is there any other kind?), khugepaged
>>> takes too long to run and find opportunities to collapse text pages.
>>> Like, days.
>>
>> Yes, in particular given that the default khugepaged settings are awful.
>>
>>>
>>>
>>> I think the test needs to be:
>>>
>>> 	if (mapping_max_folio_order(mapping) >= PMD_ORDER)
> 
> This is very helpful, since I was thinking about using
> mapping_large_folio_support().
> 
>>>
>>> as there can be cases of filesystems which support up to, say, 64KiB,
>>> but not all the way up to 2MiB.  I disapprove of this situation, but
>>> this is where we are right now.
>>
>> Right, that's what I had in mind.
> 
> Does Nico’s mTHP support for khugepaged include changes to collapse_file()?
> That might change the above test.

At least not regarding adding support for other folio sizes. Baolin
(IIRC) had a version for shmem support, but that will come after Nico's
series was merged.

-- 
Cheers,

David

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Zi Yan]

On 23 Mar 2026, at 17:21, David Hildenbrand (Arm) wrote:

> On 3/23/26 22:11, Zi Yan wrote:
>> On 23 Mar 2026, at 17:05, David Hildenbrand (Arm) wrote:
>>
>>> On 3/23/26 22:02, Matthew Wilcox wrote:
>>>>
>>>> Not necessarily that lucky; if you set VM_HUGEPAGE,
>>>> do_sync_mmap_readahead() will allocate PMD-sized folios automatically.
>>>> On busy database servers (and is there any other kind?), khugepaged
>>>> takes too long to run and find opportunities to collapse text pages.
>>>> Like, days.
>>>
>>> Yes, in particular given that the default khugepaged settings are awful.
>>>
>>>>
>>>>
>>>> I think the test needs to be:
>>>>
>>>> 	if (mapping_max_folio_order(mapping) >= PMD_ORDER)
>>
>> This is very helpful, since I was thinking about using
>> mapping_large_folio_support().
>>
>>>>
>>>> as there can be cases of filesystems which support up to, say, 64KiB,
>>>> but not all the way up to 2MiB.  I disapprove of this situation, but
>>>> this is where we are right now.
>>>
>>> Right, that's what I had in mind.
>>
>> Does Nico’s mTHP support for khugepaged include changes to collapse_file()?
>> That might change the above test.
>
> At least not regarding adding support for other folio sizes. Baolin
> (IIRC) had a version for shmem support, but that will come after Nico's
> series was merged.

Great. That makes my life easier. Thanks.

Best Regards,
Yan, Zi

Re: [RFC PATCH 10/11] selftests/mm: remove READ_ONLY_THP_FOR_FS test in khugepaged

[David Hildenbrand (Arm)]

On 3/23/26 22:07, Matthew Wilcox wrote:
> On Mon, Mar 23, 2026 at 03:06:43PM -0400, Zi Yan wrote:
>> READ_ONLY_THP_FOR_FS is no longer present, remove related test.
> 
> Um, surely we want to keep the test?  It's no longer conditional on
> READ_ONLY_THP_FOR_FS being enabled, but we still want to collapse
> mapped files.

Right, in particular this patch would also remove MADV_COLLAPSE support
(not just khugepaged support).

-- 
Cheers,

David

Re: [RFC PATCH 10/11] selftests/mm: remove READ_ONLY_THP_FOR_FS test in khugepaged

[Zi Yan]

On 24 Mar 2026, at 5:04, David Hildenbrand (Arm) wrote:

> On 3/23/26 22:07, Matthew Wilcox wrote:
>> On Mon, Mar 23, 2026 at 03:06:43PM -0400, Zi Yan wrote:
>>> READ_ONLY_THP_FOR_FS is no longer present, remove related test.
>>
>> Um, surely we want to keep the test?  It's no longer conditional on
>> READ_ONLY_THP_FOR_FS being enabled, but we still want to collapse
>> mapped files.
>
> Right, in particular this patch would also remove MADV_COLLAPSE support
> (not just khugepaged support).

I will keep these selftests in the new version, since the new one aims to enable
READ_ONLY_THP_FOR_FS by default for all FSes supporting large folio.

Best Regards,
Yan, Zi

Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Baolin Wang]

On 3/24/26 8:12 AM, Zi Yan wrote:
> On 23 Mar 2026, at 17:21, David Hildenbrand (Arm) wrote:
> 
>> On 3/23/26 22:11, Zi Yan wrote:
>>> On 23 Mar 2026, at 17:05, David Hildenbrand (Arm) wrote:
>>>
>>>> On 3/23/26 22:02, Matthew Wilcox wrote:
>>>>>
>>>>> Not necessarily that lucky; if you set VM_HUGEPAGE,
>>>>> do_sync_mmap_readahead() will allocate PMD-sized folios automatically.
>>>>> On busy database servers (and is there any other kind?), khugepaged
>>>>> takes too long to run and find opportunities to collapse text pages.
>>>>> Like, days.
>>>>
>>>> Yes, in particular given that the default khugepaged settings are awful.
>>>>
>>>>>
>>>>>
>>>>> I think the test needs to be:
>>>>>
>>>>> 	if (mapping_max_folio_order(mapping) >= PMD_ORDER)
>>>
>>> This is very helpful, since I was thinking about using
>>> mapping_large_folio_support().
>>>
>>>>>
>>>>> as there can be cases of filesystems which support up to, say, 64KiB,
>>>>> but not all the way up to 2MiB.  I disapprove of this situation, but
>>>>> this is where we are right now.
>>>>
>>>> Right, that's what I had in mind.
>>>
>>> Does Nico’s mTHP support for khugepaged include changes to collapse_file()?
>>> That might change the above test.
>>
>> At least not regarding adding support for other folio sizes. Baolin
>> (IIRC) had a version for shmem support, but that will come after Nico's
>> series was merged.

Right. Here is the link to the RFC version:

https://lore.kernel.org/all/cover.1755677674.git.baolin.wang@linux.alibaba.com/

Moreover, I have further updated my local tree based on Nico's series. I 
will send out the new version once his series is merged.