Subject: [PATCH 4/8] core: use rest_of_page() macro where appropriate

From: Yury Norov <[email-masked]>
Date: Tue, 3 Mar 2026 20:27:12 -0500

Switch core and library code to using the macro. No functional
changes intended.

Signed-off-by: Yury Norov <[email-masked]>
---
 include/crypto/scatterwalk.h |  2 +-
 include/linux/highmem.h      | 24 ++++++++++--------------
 include/linux/iomap.h        |  2 +-
 include/linux/iov_iter.h     |  3 +--
 kernel/events/ring_buffer.c  |  2 +-
 lib/bitmap-str.c             |  2 +-
 lib/iov_iter.c               |  5 ++---
 7 files changed, 17 insertions(+), 23 deletions(-)

diff --git a/include/crypto/scatterwalk.h b/include/crypto/scatterwalk.h
index 624fab589c2c..c671d5383c12 100644
--- a/include/crypto/scatterwalk.h
+++ b/include/crypto/scatterwalk.h
@@ -73,7 +73,7 @@ static inline unsigned int scatterwalk_clamp(struct scatter_walk *walk,
 	 * page due to the data not being aligned to the algorithm's alignmask.
 	 */
 	if (IS_ENABLED(CONFIG_HIGHMEM))
-		limit = PAGE_SIZE - offset_in_page(walk->offset);
+		limit = rest_of_page(walk->offset);
 	else
 		limit = PAGE_SIZE;
 
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index af03db851a1d..05528ba886fb 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -507,12 +507,10 @@ static inline void memcpy_folio(struct folio *dst_folio, size_t dst_off,
 		const char *src = kmap_local_folio(src_folio, src_off);
 		size_t chunk = len;
 
-		if (folio_test_highmem(dst_folio) &&
-		    chunk > PAGE_SIZE - offset_in_page(dst_off))
-			chunk = PAGE_SIZE - offset_in_page(dst_off);
-		if (folio_test_highmem(src_folio) &&
-		    chunk > PAGE_SIZE - offset_in_page(src_off))
-			chunk = PAGE_SIZE - offset_in_page(src_off);
+		if (folio_test_highmem(dst_folio) && chunk > rest_of_page(dst_off))
+			chunk = rest_of_page(dst_off);
+		if (folio_test_highmem(src_folio) && chunk > rest_of_page(src_off))
+			chunk = rest_of_page(src_off);
 		memcpy(dst, src, chunk);
 		kunmap_local(src);
 		kunmap_local(dst);
@@ -580,9 +578,8 @@ 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_partial_kmap(folio) &&
-		    chunk > PAGE_SIZE - offset_in_page(offset))
-			chunk = PAGE_SIZE - offset_in_page(offset);
+		if (folio_test_partial_kmap(folio) && chunk > rest_of_page(offset))
+			chunk = rest_of_page(offset);
 		memcpy(to, from, chunk);
 		kunmap_local(from);
 
@@ -608,9 +605,8 @@ 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_partial_kmap(folio) &&
-		    chunk > PAGE_SIZE - offset_in_page(offset))
-			chunk = PAGE_SIZE - offset_in_page(offset);
+		if (folio_test_partial_kmap(folio) && chunk > rest_of_page(offset))
+			chunk = rest_of_page(offset);
 		memcpy(to, from, chunk);
 		kunmap_local(to);
 
@@ -642,7 +638,7 @@ static inline __must_check void *folio_zero_tail(struct folio *folio,
 	size_t len = folio_size(folio) - offset;
 
 	if (folio_test_partial_kmap(folio)) {
-		size_t max = PAGE_SIZE - offset_in_page(offset);
+		size_t max = rest_of_page(offset);
 
 		while (len > max) {
 			memset(kaddr, 0, max);
@@ -680,7 +676,7 @@ static inline void folio_fill_tail(struct folio *folio, size_t offset,
 	VM_BUG_ON(offset + len > folio_size(folio));
 
 	if (folio_test_partial_kmap(folio)) {
-		size_t max = PAGE_SIZE - offset_in_page(offset);
+		size_t max = rest_of_page(offset);
 
 		while (len > max) {
 			memcpy(to, from, max);
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 99b7209dabd7..6ae549192adb 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -142,7 +142,7 @@ static inline void *iomap_inline_data(const struct iomap *iomap, loff_t pos)
  */
 static inline bool iomap_inline_data_valid(const struct iomap *iomap)
 {
-	return iomap->length <= PAGE_SIZE - offset_in_page(iomap->inline_data);
+	return iomap->length <= rest_of_page(iomap->inline_data);
 }
 
 /*
diff --git a/include/linux/iov_iter.h b/include/linux/iov_iter.h
index f9a17fbbd398..13a9ee653ef8 100644
--- a/include/linux/iov_iter.h
+++ b/include/linux/iov_iter.h
@@ -227,8 +227,7 @@ size_t iterate_xarray(struct iov_iter *iter, size_t len, void *priv, void *priv2
 		while (flen) {
 			void *base = kmap_local_folio(folio, offset);
 
-			part = min_t(size_t, flen,
-				     PAGE_SIZE - offset_in_page(offset));
+			part = min_t(size_t, flen, rest_of_page(offset));
 			remain = step(base, progress, part, priv, priv2);
 			kunmap_local(base);
 
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 3e7de2661417..1db2868b90c9 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -590,7 +590,7 @@ long perf_output_copy_aux(struct perf_output_handle *aux_handle,
 	to &= (rb->aux_nr_pages << PAGE_SHIFT) - 1;
 
 	do {
-		tocopy = PAGE_SIZE - offset_in_page(from);
+		tocopy = rest_of_page(from);
 		if (to > from)
 			tocopy = min(tocopy, to - from);
 		if (!tocopy)
diff --git a/lib/bitmap-str.c b/lib/bitmap-str.c
index be745209507a..a357342d5d6c 100644
--- a/lib/bitmap-str.c
+++ b/lib/bitmap-str.c
@@ -58,7 +58,7 @@ EXPORT_SYMBOL(bitmap_parse_user);
 int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
 			    int nmaskbits)
 {
-	ptrdiff_t len = PAGE_SIZE - offset_in_page(buf);
+	ptrdiff_t len = rest_of_page(buf);
 
 	return list ? scnprintf(buf, len, "%*pbl\n", nmaskbits, maskp) :
 		      scnprintf(buf, len, "%*pb\n", nmaskbits, maskp);
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 0a63c7fba313..c7e812349ca2 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -483,9 +483,8 @@ size_t copy_folio_from_iter_atomic(struct folio *folio, size_t offset,
 		char *to = kmap_local_folio(folio, offset);
 
 		n = bytes - copied;
-		if (folio_test_partial_kmap(folio) &&
-		    n > PAGE_SIZE - offset_in_page(offset))
-			n = PAGE_SIZE - offset_in_page(offset);
+		if (folio_test_partial_kmap(folio) && n > rest_of_page(offset))
+			n = rest_of_page(offset);
 
 		pagefault_disable();
 		n = __copy_from_iter(to, n, i);
-- 
2.43.0