[PATCH 0/3] Remove copy_page_from_iter_atomic()

[PATCH 0/3] Remove copy_page_from_iter_atomic()

[Matthew Wilcox (Oracle)]

The first patch here is a bug-fix that enables
CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP to work correctly with
filesystems that support large folios.  Then we convert ntfs3 to use
copy_folio_from_iter_atomic() instead of copy_page_from_iter_atomic()
and finally remove copy_page_from_iter_atomic().

Matthew Wilcox (Oracle) (3):
  highmem: Add folio_test_partial_kmap()
  ntfs3: Use folios more in ntfs_compress_write()
  iov: Remove copy_page_from_iter_atomic()

 fs/ntfs3/file.c            | 31 +++++++++++++------------------
 include/linux/highmem.h    | 10 +++++-----
 include/linux/page-flags.h |  7 +++++++
 include/linux/uio.h        | 10 ++--------
 lib/iov_iter.c             | 29 +++++++++++++----------------
 5 files changed, 40 insertions(+), 47 deletions(-)

-- 
2.47.2

[PATCH 1/3] highmem: Add folio_test_partial_kmap()

[Matthew Wilcox (Oracle)]

In commit c749d9b7ebbc (iov_iter: fix copy_page_from_iter_atomic() if
KMAP_LOCAL_FORCE_MAP), Hugh correctly noted that if KMAP_LOCAL_FORCE_MAP
is enabled, we must limit ourselves to PAGE_SIZE bytes per call
to kmap_local().  The same problem exists in memcpy_from_folio(),
memcpy_to_folio(), folio_zero_tail(), folio_fill_tail() and
memcpy_from_file_folio(), so add folio_test_partial_kmap() to do this
more succinctly.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Fixes: 00cdf76012ab (mm: add memcpy_from_file_folio())
Cc: stable@vger.kernel.org
---
 include/linux/highmem.h    | 10 +++++-----
 include/linux/page-flags.h |  7 +++++++
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 5c6bea81a90e..c698f8415675 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -461,7 +461,7 @@ static inline void memcpy_from_folio(char *to, struct folio *folio,
 		const char *from = kmap_local_folio(folio, offset);
 		size_t chunk = len;
 
-		if (folio_test_highmem(folio) &&
+		if (folio_test_partial_kmap(folio) &&
 		    chunk > PAGE_SIZE - offset_in_page(offset))
 			chunk = PAGE_SIZE - offset_in_page(offset);
 		memcpy(to, from, chunk);
@@ -489,7 +489,7 @@ static inline void memcpy_to_folio(struct folio *folio, size_t offset,
 		char *to = kmap_local_folio(folio, offset);
 		size_t chunk = len;
 
-		if (folio_test_highmem(folio) &&
+		if (folio_test_partial_kmap(folio) &&
 		    chunk > PAGE_SIZE - offset_in_page(offset))
 			chunk = PAGE_SIZE - offset_in_page(offset);
 		memcpy(to, from, chunk);
@@ -522,7 +522,7 @@ static inline __must_check void *folio_zero_tail(struct folio *folio,
 {
 	size_t len = folio_size(folio) - offset;
 
-	if (folio_test_highmem(folio)) {
+	if (folio_test_partial_kmap(folio)) {
 		size_t max = PAGE_SIZE - offset_in_page(offset);
 
 		while (len > max) {
@@ -560,7 +560,7 @@ static inline void folio_fill_tail(struct folio *folio, size_t offset,
 
 	VM_BUG_ON(offset + len > folio_size(folio));
 
-	if (folio_test_highmem(folio)) {
+	if (folio_test_partial_kmap(folio)) {
 		size_t max = PAGE_SIZE - offset_in_page(offset);
 
 		while (len > max) {
@@ -597,7 +597,7 @@ static inline size_t memcpy_from_file_folio(char *to, struct folio *folio,
 	size_t offset = offset_in_folio(folio, pos);
 	char *from = kmap_local_folio(folio, offset);
 
-	if (folio_test_highmem(folio)) {
+	if (folio_test_partial_kmap(folio)) {
 		offset = offset_in_page(offset);
 		len = min_t(size_t, len, PAGE_SIZE - offset);
 	} else
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e6a21b62dcce..3b814ce08331 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -615,6 +615,13 @@ FOLIO_FLAG(dropbehind, FOLIO_HEAD_PAGE)
 PAGEFLAG_FALSE(HighMem, highmem)
 #endif
 
+/* Does kmap_local_folio() only allow access to one page of the folio? */
+#ifdef CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP
+#define folio_test_partial_kmap(f)	true
+#else
+#define folio_test_partial_kmap(f)	folio_test_highmem(f)
+#endif
+
 #ifdef CONFIG_SWAP
 static __always_inline bool folio_test_swapcache(const struct folio *folio)
 {
-- 
2.47.2

[PATCH 2/3] ntfs3: Use folios more in ntfs_compress_write()

[Matthew Wilcox (Oracle)]

Remove the local 'page' variable and do everything in terms of folios.
Removes the last user of copy_page_from_iter_atomic() and a hidden
call to compound_head() in ClearPageDirty().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/ntfs3/file.c | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/fs/ntfs3/file.c b/fs/ntfs3/file.c
index 9b6a3f8d2e7c..bc6062e0668e 100644
--- a/fs/ntfs3/file.c
+++ b/fs/ntfs3/file.c
@@ -998,7 +998,8 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 	struct ntfs_inode *ni = ntfs_i(inode);
 	u64 valid = ni->i_valid;
 	struct ntfs_sb_info *sbi = ni->mi.sbi;
-	struct page *page, **pages = NULL;
+	struct page **pages = NULL;
+	struct folio *folio;
 	size_t written = 0;
 	u8 frame_bits = NTFS_LZNT_CUNIT + sbi->cluster_bits;
 	u32 frame_size = 1u << frame_bits;
@@ -1008,7 +1009,6 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 	u64 frame_vbo;
 	pgoff_t index;
 	bool frame_uptodate;
-	struct folio *folio;
 
 	if (frame_size < PAGE_SIZE) {
 		/*
@@ -1062,8 +1062,7 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 					    pages_per_frame);
 			if (err) {
 				for (ip = 0; ip < pages_per_frame; ip++) {
-					page = pages[ip];
-					folio = page_folio(page);
+					folio = page_folio(pages[ip]);
 					folio_unlock(folio);
 					folio_put(folio);
 				}
@@ -1074,10 +1073,9 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 		ip = off >> PAGE_SHIFT;
 		off = offset_in_page(valid);
 		for (; ip < pages_per_frame; ip++, off = 0) {
-			page = pages[ip];
-			folio = page_folio(page);
-			zero_user_segment(page, off, PAGE_SIZE);
-			flush_dcache_page(page);
+			folio = page_folio(pages[ip]);
+			folio_zero_segment(folio, off, PAGE_SIZE);
+			flush_dcache_folio(folio);
 			folio_mark_uptodate(folio);
 		}
 
@@ -1086,8 +1084,7 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 		ni_unlock(ni);
 
 		for (ip = 0; ip < pages_per_frame; ip++) {
-			page = pages[ip];
-			folio = page_folio(page);
+			folio = page_folio(pages[ip]);
 			folio_mark_uptodate(folio);
 			folio_unlock(folio);
 			folio_put(folio);
@@ -1131,8 +1128,7 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 				if (err) {
 					for (ip = 0; ip < pages_per_frame;
 					     ip++) {
-						page = pages[ip];
-						folio = page_folio(page);
+						folio = page_folio(pages[ip]);
 						folio_unlock(folio);
 						folio_put(folio);
 					}
@@ -1150,10 +1146,10 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 		for (;;) {
 			size_t cp, tail = PAGE_SIZE - off;
 
-			page = pages[ip];
-			cp = copy_page_from_iter_atomic(page, off,
+			folio = page_folio(pages[ip]);
+			cp = copy_folio_from_iter_atomic(folio, off,
 							min(tail, bytes), from);
-			flush_dcache_page(page);
+			flush_dcache_folio(folio);
 
 			copied += cp;
 			bytes -= cp;
@@ -1173,9 +1169,8 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
 		ni_unlock(ni);
 
 		for (ip = 0; ip < pages_per_frame; ip++) {
-			page = pages[ip];
-			ClearPageDirty(page);
-			folio = page_folio(page);
+			folio = page_folio(pages[ip]);
+			folio_clear_dirty(folio);
 			folio_mark_uptodate(folio);
 			folio_unlock(folio);
 			folio_put(folio);
-- 
2.47.2

Re: [PATCH 2/3] ntfs3: Use folios more in ntfs_compress_write()

[Konstantin Komarov]

On 5/14/25 19:06, Matthew Wilcox (Oracle) wrote:
> Remove the local 'page' variable and do everything in terms of folios.
> Removes the last user of copy_page_from_iter_atomic() and a hidden
> call to compound_head() in ClearPageDirty().
>
> Signed-off-by: Matthew Wilcox (Oracle)<willy@infradead.org>
> ---
>   fs/ntfs3/file.c | 31 +++++++++++++------------------
>   1 file changed, 13 insertions(+), 18 deletions(-)
>
> diff --git a/fs/ntfs3/file.c b/fs/ntfs3/file.c
> index 9b6a3f8d2e7c..bc6062e0668e 100644
> --- a/fs/ntfs3/file.c
> +++ b/fs/ntfs3/file.c
> @@ -998,7 +998,8 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   	struct ntfs_inode *ni = ntfs_i(inode);
>   	u64 valid = ni->i_valid;
>   	struct ntfs_sb_info *sbi = ni->mi.sbi;
> -	struct page *page, **pages = NULL;
> +	struct page **pages = NULL;
> +	struct folio *folio;
>   	size_t written = 0;
>   	u8 frame_bits = NTFS_LZNT_CUNIT + sbi->cluster_bits;
>   	u32 frame_size = 1u << frame_bits;
> @@ -1008,7 +1009,6 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   	u64 frame_vbo;
>   	pgoff_t index;
>   	bool frame_uptodate;
> -	struct folio *folio;
>   
>   	if (frame_size < PAGE_SIZE) {
>   		/*
> @@ -1062,8 +1062,7 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   					    pages_per_frame);
>   			if (err) {
>   				for (ip = 0; ip < pages_per_frame; ip++) {
> -					page = pages[ip];
> -					folio = page_folio(page);
> +					folio = page_folio(pages[ip]);
>   					folio_unlock(folio);
>   					folio_put(folio);
>   				}
> @@ -1074,10 +1073,9 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   		ip = off >> PAGE_SHIFT;
>   		off = offset_in_page(valid);
>   		for (; ip < pages_per_frame; ip++, off = 0) {
> -			page = pages[ip];
> -			folio = page_folio(page);
> -			zero_user_segment(page, off, PAGE_SIZE);
> -			flush_dcache_page(page);
> +			folio = page_folio(pages[ip]);
> +			folio_zero_segment(folio, off, PAGE_SIZE);
> +			flush_dcache_folio(folio);
>   			folio_mark_uptodate(folio);
>   		}
>   
> @@ -1086,8 +1084,7 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   		ni_unlock(ni);
>   
>   		for (ip = 0; ip < pages_per_frame; ip++) {
> -			page = pages[ip];
> -			folio = page_folio(page);
> +			folio = page_folio(pages[ip]);
>   			folio_mark_uptodate(folio);
>   			folio_unlock(folio);
>   			folio_put(folio);
> @@ -1131,8 +1128,7 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   				if (err) {
>   					for (ip = 0; ip < pages_per_frame;
>   					     ip++) {
> -						page = pages[ip];
> -						folio = page_folio(page);
> +						folio = page_folio(pages[ip]);
>   						folio_unlock(folio);
>   						folio_put(folio);
>   					}
> @@ -1150,10 +1146,10 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   		for (;;) {
>   			size_t cp, tail = PAGE_SIZE - off;
>   
> -			page = pages[ip];
> -			cp = copy_page_from_iter_atomic(page, off,
> +			folio = page_folio(pages[ip]);
> +			cp = copy_folio_from_iter_atomic(folio, off,
>   							min(tail, bytes), from);
> -			flush_dcache_page(page);
> +			flush_dcache_folio(folio);
>   
>   			copied += cp;
>   			bytes -= cp;
> @@ -1173,9 +1169,8 @@ static ssize_t ntfs_compress_write(struct kiocb *iocb, struct iov_iter *from)
>   		ni_unlock(ni);
>   
>   		for (ip = 0; ip < pages_per_frame; ip++) {
> -			page = pages[ip];
> -			ClearPageDirty(page);
> -			folio = page_folio(page);
> +			folio = page_folio(pages[ip]);
> +			folio_clear_dirty(folio);
>   			folio_mark_uptodate(folio);
>   			folio_unlock(folio);
>   			folio_put(folio);

The changes look fine. Feel free to add them.

[PATCH 3/3] iov: Remove copy_page_from_iter_atomic()

[Matthew Wilcox (Oracle)]

All callers now use copy_folio_from_iter_atomic(), so convert
copy_page_from_iter_atomic().  While I'm in there, use kmap_local_folio()
and pagefault_disable() instead of kmap_atomic().  That allows preemption
and/or task migration to happen during the copy_from_user().  Also use
the new folio_test_partial_kmap() predicate instead of open-coding it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/uio.h | 10 ++--------
 lib/iov_iter.c      | 29 +++++++++++++----------------
 2 files changed, 15 insertions(+), 24 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 49ece9e1888f..e46477482663 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -176,8 +176,6 @@ static inline size_t iov_length(const struct iovec *iov, unsigned long nr_segs)
 	return ret;
 }
 
-size_t copy_page_from_iter_atomic(struct page *page, size_t offset,
-				  size_t bytes, struct iov_iter *i);
 void iov_iter_advance(struct iov_iter *i, size_t bytes);
 void iov_iter_revert(struct iov_iter *i, size_t bytes);
 size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t bytes);
@@ -187,6 +185,8 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);
 size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);
+size_t copy_folio_from_iter_atomic(struct folio *folio, size_t offset,
+		size_t bytes, struct iov_iter *i);
 
 size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
 size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
@@ -204,12 +204,6 @@ static inline size_t copy_folio_from_iter(struct folio *folio, size_t offset,
 	return copy_page_from_iter(&folio->page, offset, bytes, i);
 }
 
-static inline size_t copy_folio_from_iter_atomic(struct folio *folio,
-		size_t offset, size_t bytes, struct iov_iter *i)
-{
-	return copy_page_from_iter_atomic(&folio->page, offset, bytes, i);
-}
-
 size_t copy_page_to_iter_nofault(struct page *page, unsigned offset,
 				 size_t bytes, struct iov_iter *i);
 
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index d9e19fb2dcf3..969d4ad510df 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -457,38 +457,35 @@ size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
 }
 EXPORT_SYMBOL(iov_iter_zero);
 
-size_t copy_page_from_iter_atomic(struct page *page, size_t offset,
+size_t copy_folio_from_iter_atomic(struct folio *folio, size_t offset,
 		size_t bytes, struct iov_iter *i)
 {
 	size_t n, copied = 0;
-	bool uses_kmap = IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP) ||
-			 PageHighMem(page);
 
-	if (!page_copy_sane(page, offset, bytes))
+	if (!page_copy_sane(&folio->page, offset, bytes))
 		return 0;
 	if (WARN_ON_ONCE(!i->data_source))
 		return 0;
 
 	do {
-		char *p;
+		char *to = kmap_local_folio(folio, offset);
 
 		n = bytes - copied;
-		if (uses_kmap) {
-			page += offset / PAGE_SIZE;
-			offset %= PAGE_SIZE;
-			n = min_t(size_t, n, PAGE_SIZE - offset);
-		}
-
-		p = kmap_atomic(page) + offset;
-		n = __copy_from_iter(p, n, i);
-		kunmap_atomic(p);
+		if (folio_test_partial_kmap(folio) &&
+		    n > PAGE_SIZE - offset_in_page(offset))
+			n = PAGE_SIZE - offset_in_page(offset);
+
+		pagefault_disable();
+		n = __copy_from_iter(to, n, i);
+		pagefault_enable();
+		kunmap_local(to);
 		copied += n;
 		offset += n;
-	} while (uses_kmap && copied != bytes && n > 0);
+	} while (copied != bytes && n > 0);
 
 	return copied;
 }
-EXPORT_SYMBOL(copy_page_from_iter_atomic);
+EXPORT_SYMBOL(copy_folio_from_iter_atomic);
 
 static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
 {
-- 
2.47.2