[PATCH v1 00/10] Remove READ_ONLY_THP_FOR_FS Kconfig

[PATCH v1 00/10] Remove READ_ONLY_THP_FOR_FS Kconfig

[Zi Yan]

Hi all,

This patchset removes READ_ONLY_THP_FOR_FS Kconfig and enables creating
read-only THPs for FSes with large folio support (the supported orders
need to include PMD_ORDER) by default.

The changes are:
1. collapse_file() from mm/khugepaged.c, instead of checking
   CONFIG_READ_ONLY_THP_FOR_FS, makes sure the mapping_max_folio_order()
   of struct address_space of the file is at least PMD_ORDER.
2. file_thp_enabled() also checks mapping_max_folio_order() instead.
3. truncate_inode_partial_folio() calls folio_split() directly instead
   of the removed try_folio_split_to_order(), since large folios can
   only show up on a FS with large folio support.
4. nr_thps is removed from struct address_space, since it is no longer
   needed to drop all read-only THPs from a FS without large folio
   support when the fd becomes writable. Its related filemap_nr_thps*()
   are removed too.
5. folio_check_splittable() no longer checks READ_ONLY_THP_FOR_FS.
6. Updated comments in various places.

Changelog
===
From RFC[1]:
1. instead of removing READ_ONLY_THP_FOR_FS function entirely, turn it
   on by default for all FSes with large folio support and the supported
   orders includes PMD_ORDER.

Suggestions and comments are welcome.

Link: https://lore.kernel.org/all/20260323190644.1714379-1-ziy@nvidia.com/ [1]

Zi Yan (10):
  mm: remove READ_ONLY_THP_FOR_FS Kconfig option
  mm/khugepaged: remove READ_ONLY_THP_FOR_FS check
  mm: fs: remove filemap_nr_thps*() functions and their users
  fs: remove nr_thps from struct address_space
  mm/huge_memory: remove READ_ONLY_THP_FOR_FS from file_thp_enabled()
  mm/huge_memory: remove folio split check for READ_ONLY_THP_FOR_FS
  mm/truncate: use folio_split() in truncate_inode_partial_folio()
  fs/btrfs: remove a comment referring to READ_ONLY_THP_FOR_FS
  selftests/mm: remove READ_ONLY_THP_FOR_FS in khugepaged
  selftests/mm: remove READ_ONLY_THP_FOR_FS from comments 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                    | 25 ++-------------
 include/linux/pagemap.h                    | 29 -----------------
 mm/Kconfig                                 | 11 -------
 mm/filemap.c                               |  1 -
 mm/huge_memory.c                           | 29 ++---------------
 mm/khugepaged.c                            | 36 +++++-----------------
 mm/truncate.c                              |  8 ++---
 tools/testing/selftests/mm/guard-regions.c |  9 +++---
 tools/testing/selftests/mm/khugepaged.c    |  4 +--
 13 files changed, 23 insertions(+), 167 deletions(-)

-- 
2.43.0

[PATCH v1 01/10] 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

Re: [PATCH v1 01/10] mm: remove READ_ONLY_THP_FOR_FS Kconfig option

[Lorenzo Stoakes (Oracle)]

On Thu, Mar 26, 2026 at 09:42:46PM -0400, Zi Yan wrote:
> 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>

Seems a reasonable ordering, so:

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

> ---
>  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
>

[PATCH v1 02/10] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

[Zi Yan]

collapse_file() requires FSes supporting large folio with at least
PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. shmem with
huge option turned on also sets large folio order on mapping, so the check
also applies to shmem.

While at it, replace VM_BUG_ON with returning failure values.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/khugepaged.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index d06d84219e1b..45b12ffb1550 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1899,8 +1899,11 @@ 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_BUG_ON(start & (HPAGE_PMD_NR - 1));
+	/* "huge" shmem sets mapping folio order and passes the check below */
+	if (mapping_max_folio_order(mapping) < PMD_ORDER)
+		return SCAN_FAIL;
+	if (start & (HPAGE_PMD_NR - 1))
+		return SCAN_ADDRESS_RANGE;
 
 	result = alloc_charge_folio(&new_folio, mm, cc);
 	if (result != SCAN_SUCCEED)
-- 
2.43.0

Re: [PATCH v1 02/10] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

[Lance Yang]

On Thu, Mar 26, 2026 at 09:42:47PM -0400, Zi Yan wrote:
>collapse_file() requires FSes supporting large folio with at least
>PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. shmem with
>huge option turned on also sets large folio order on mapping, so the check
>also applies to shmem.
>
>While at it, replace VM_BUG_ON with returning failure values.
>
>Signed-off-by: Zi Yan <ziy@nvidia.com>
>---
> mm/khugepaged.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
>diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>index d06d84219e1b..45b12ffb1550 100644
>--- a/mm/khugepaged.c
>+++ b/mm/khugepaged.c
>@@ -1899,8 +1899,11 @@ 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_BUG_ON(start & (HPAGE_PMD_NR - 1));
>+	/* "huge" shmem sets mapping folio order and passes the check below */
>+	if (mapping_max_folio_order(mapping) < PMD_ORDER)
>+		return SCAN_FAIL;

Yep, for shmem inodes, if the mount has huge= enabled, inode creation
marks the mapping are large-folio capable:

	/* Don't consider 'deny' for emergencies and 'force' for testing */
	if (sbinfo->huge)
		mapping_set_large_folios(inode->i_mapping);

LGTM!

Reviewed-by: Lance Yang <lance.yang@linux.dev>

Re: [PATCH v1 02/10] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

[Lance Yang]

On 2026/3/27 15:29, Lance Yang wrote:
> 
> On Thu, Mar 26, 2026 at 09:42:47PM -0400, Zi Yan wrote:
>> collapse_file() requires FSes supporting large folio with at least
>> PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. shmem with
>> huge option turned on also sets large folio order on mapping, so the check
>> also applies to shmem.
>>
>> While at it, replace VM_BUG_ON with returning failure values.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>> mm/khugepaged.c | 7 +++++--
>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index d06d84219e1b..45b12ffb1550 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -1899,8 +1899,11 @@ 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_BUG_ON(start & (HPAGE_PMD_NR - 1));
>> +	/* "huge" shmem sets mapping folio order and passes the check below */
>> +	if (mapping_max_folio_order(mapping) < PMD_ORDER)
>> +		return SCAN_FAIL;
> 
> Yep, for shmem inodes, if the mount has huge= enabled, inode creation
> marks the mapping are large-folio capable:

Oops, s/are/as/

> 
> 	/* Don't consider 'deny' for emergencies and 'force' for testing */
> 	if (sbinfo->huge)
> 		mapping_set_large_folios(inode->i_mapping);
> 
> LGTM!
> 
> Reviewed-by: Lance Yang <lance.yang@linux.dev>

Re: [PATCH v1 02/10] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

[Baolin Wang]

On 3/27/26 9:42 AM, Zi Yan wrote:
> collapse_file() requires FSes supporting large folio with at least
> PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. shmem with
> huge option turned on also sets large folio order on mapping, so the check
> also applies to shmem.
> 
> While at it, replace VM_BUG_ON with returning failure values.
> 
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
>   mm/khugepaged.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index d06d84219e1b..45b12ffb1550 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1899,8 +1899,11 @@ 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_BUG_ON(start & (HPAGE_PMD_NR - 1));
> +	/* "huge" shmem sets mapping folio order and passes the check below */
> +	if (mapping_max_folio_order(mapping) < PMD_ORDER)
> +		return SCAN_FAIL;

This is not true for anonymous shmem, since its large order allocation 
logic is similar to anonymous memory. That means it will not call 
mapping_set_large_folios() for anonymous shmem.

So I think the check should be:

if (!is_shmem && mapping_max_folio_order(mapping) < PMD_ORDER)
      return SCAN_FAIL;

[PATCH v1 03/10] mm: fs: remove filemap_nr_thps*() functions and their users

[Zi Yan]

They are used by READ_ONLY_THP_FOR_FS to handle writes to FSes without
large folio support, so that read-only THPs created in these FSes are not
seen by the FSes when the underlying fd becomes writable. Now read-only PMD
THPs only appear in a FS with large folio support and the supported orders
include PMD_ORDRE.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 fs/open.c               | 27 ---------------------------
 include/linux/pagemap.h | 29 -----------------------------
 mm/filemap.c            |  1 -
 mm/huge_memory.c        |  1 -
 mm/khugepaged.c         | 29 ++---------------------------
 5 files changed, 2 insertions(+), 85 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:
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 b2a6060b3c20..c7873dbdc470 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3833,7 +3833,6 @@ 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);
 				}
 			}
 		}
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 45b12ffb1550..8004ab8de6d2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2104,20 +2104,8 @@ 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);
-		}
-	}
+	if (!is_shmem && inode_is_open_for_write(mapping->host))
+		result = SCAN_FAIL;
 
 xa_locked:
 	xas_unlock_irq(&xas);
@@ -2296,19 +2284,6 @@ 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

Re: [PATCH v1 03/10] mm: fs: remove filemap_nr_thps*() functions and their users

[Lance Yang]

On 2026/3/27 09:42, Zi Yan wrote:
> They are used by READ_ONLY_THP_FOR_FS to handle writes to FSes without
> large folio support, so that read-only THPs created in these FSes are not
> seen by the FSes when the underlying fd becomes writable. Now read-only PMD
> THPs only appear in a FS with large folio support and the supported orders
> include PMD_ORDRE.
> 
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---

LGTM, feel free to add:

Reviewed-by: Lance Yang <lance.yang@linux.dev>

[PATCH v1 04/10] fs: remove nr_thps from struct address_space

[Zi Yan]

filemap_nr_thps*() are removed, the related field, address_space->nr_thps,
is no longer needed. Remove it.

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

[PATCH v1 05/10] mm/huge_memory: remove READ_ONLY_THP_FOR_FS from file_thp_enabled()

[Zi Yan]

Replace it with a check on the max folio order of the file's address space
mapping, making sure PMD_ORDER is supported.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/huge_memory.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c7873dbdc470..1da1467328a3 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -89,9 +89,6 @@ 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;
 
@@ -100,6 +97,9 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
 	if (IS_ANON_FILE(inode))
 		return false;
 
+	if (mapping_max_folio_order(inode->i_mapping) < PMD_ORDER)
+		return false;
+
 	return !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
 }
 
-- 
2.43.0

[PATCH v1 06/10] 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 1da1467328a3..30eddcbf86f1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3732,28 +3732,6 @@ 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

[PATCH v1 07/10] 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 | 25 ++-----------------------
 mm/truncate.c           |  8 ++++----
 2 files changed, 6 insertions(+), 27 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 1258fa37e85b..171de8138e98 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);
@@ -641,8 +620,8 @@ 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)
+static inline int folio_split(struct folio *folio, unsigned int new_order,
+		struct page *page, struct list_head *list);
 {
 	VM_WARN_ON_ONCE_FOLIO(1, folio);
 	return -EINVAL;
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

Re: [PATCH v1 07/10] mm/truncate: use folio_split() in truncate_inode_partial_folio()

[Lance Yang]

On 2026/3/27 09:42, Zi Yan wrote:
> 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 | 25 ++-----------------------
>   mm/truncate.c           |  8 ++++----
>   2 files changed, 6 insertions(+), 27 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 1258fa37e85b..171de8138e98 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);
> @@ -641,8 +620,8 @@ 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)
> +static inline int folio_split(struct folio *folio, unsigned int new_order,
> +		struct page *page, struct list_head *list);

Ouch, that ';' wasn't supposed to be there, right?

[PATCH v1 08/10] 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>
Acked-by: David Sterba <dsterba@suse.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

[PATCH v1 09/10] selftests/mm: remove READ_ONLY_THP_FOR_FS in khugepaged

[Zi Yan]

Change the requirement to a file system with large folio support and the
supported order needs to include PMD_ORDER.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 tools/testing/selftests/mm/khugepaged.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 3fe7ef04ac62..bdcdd31beb1e 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1086,8 +1086,8 @@ static void usage(void)
 	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, "\n\t\"file,all\" mem_type requires a file system\n");
+	fprintf(stderr,	"\twith large folio support (order >= PMD order)\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");
-- 
2.43.0

[PATCH v1 10/10] selftests/mm: remove READ_ONLY_THP_FOR_FS from comments in guard-regions

[Zi Yan]

Any file system with large folio support and the supported orders include
PMD_ORDER can be used.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 tools/testing/selftests/mm/guard-regions.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c
index 48e8b1539be3..13e77e48b6ef 100644
--- a/tools/testing/selftests/mm/guard-regions.c
+++ b/tools/testing/selftests/mm/guard-regions.c
@@ -2205,7 +2205,7 @@ TEST_F(guard_regions, collapse)
 
 	/*
 	 * We must close and re-open local-file backed as read-only for
-	 * CONFIG_READ_ONLY_THP_FOR_FS to work.
+	 * MADV_COLLAPSE to work.
 	 */
 	if (variant->backing == LOCAL_FILE_BACKED) {
 		ASSERT_EQ(close(self->fd), 0);
@@ -2237,9 +2237,10 @@ TEST_F(guard_regions, collapse)
 	/*
 	 * 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.
+	 * The madvise() call will also fail if the file system does not support
+	 * large folio or the supported orders do not include PMD_ORDER for the
+	 * local file case, but we can't differentiate whether this occurred or
+	 * if the collapse was rightly rejected.
 	 */
 	EXPECT_NE(madvise(ptr, size, MADV_COLLAPSE), 0);
 
-- 
2.43.0