linux-kernel - [PATCH] scatterlist: inline sg

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Message-ID: <20250416160615.3571958-1-csander@purestorage.com>
Date: Wed, 16 Apr 2025 10:06:13 -0600
From: Caleb Sander Mateos <csander@...estorage.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org,
	linux-block@...r.kernel.org,
	Caleb Sander Mateos <csander@...estorage.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] scatterlist: inline sg_next()

sg_next() is a short function called frequently in I/O paths. Define it
in the header file so it can be inlined into its callers.

Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
---
Is it a concern that this would break kernel modules built against old headers?
If so, I could update the patch to continue compiling and exporting sg_next() in
scatterlist.c.

 include/linux/scatterlist.h | 23 ++++++++++++++++++++++-
 lib/scatterlist.c           | 23 -----------------------
 2 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 138e2f1bd08f..0cdbfc42f153 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -92,10 +92,32 @@ static inline bool sg_is_chain(struct scatterlist *sg)
 static inline bool sg_is_last(struct scatterlist *sg)
 {
 	return __sg_flags(sg) & SG_END;
 }
 
+/**
+ * sg_next - return the next scatterlist entry in a list
+ * @sg:		The current sg entry
+ *
+ * Description:
+ *   Usually the next entry will be @sg@ + 1, but if this sg element is part
+ *   of a chained scatterlist, it could jump to the start of a new
+ *   scatterlist array.
+ *
+ **/
+static inline struct scatterlist *sg_next(struct scatterlist *sg)
+{
+	if (sg_is_last(sg))
+		return NULL;
+
+	sg++;
+	if (unlikely(sg_is_chain(sg)))
+		sg = sg_chain_ptr(sg);
+
+	return sg;
+}
+
 /**
  * sg_assign_page - Assign a given page to an SG entry
  * @sg:		    SG entry
  * @page:	    The page
  *
@@ -416,11 +438,10 @@ static inline void sg_init_marker(struct scatterlist *sgl,
 	sg_mark_end(&sgl[nents - 1]);
 }
 
 int sg_nents(struct scatterlist *sg);
 int sg_nents_for_len(struct scatterlist *sg, u64 len);
-struct scatterlist *sg_next(struct scatterlist *);
 struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
 void sg_init_table(struct scatterlist *, unsigned int);
 void sg_init_one(struct scatterlist *, const void *, unsigned int);
 int sg_split(struct scatterlist *in, const int in_mapped_nents,
 	     const off_t skip, const int nb_splits,
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index b58d5ef1a34b..7582dfab7fe3 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -11,33 +11,10 @@
 #include <linux/kmemleak.h>
 #include <linux/bvec.h>
 #include <linux/uio.h>
 #include <linux/folio_queue.h>
 
-/**
- * sg_next - return the next scatterlist entry in a list
- * @sg:		The current sg entry
- *
- * Description:
- *   Usually the next entry will be @sg@ + 1, but if this sg element is part
- *   of a chained scatterlist, it could jump to the start of a new
- *   scatterlist array.
- *
- **/
-struct scatterlist *sg_next(struct scatterlist *sg)
-{
-	if (sg_is_last(sg))
-		return NULL;
-
-	sg++;
-	if (unlikely(sg_is_chain(sg)))
-		sg = sg_chain_ptr(sg);
-
-	return sg;
-}
-EXPORT_SYMBOL(sg_next);
-
 /**
  * sg_nents - return total count of entries in scatterlist
  * @sg:		The scatterlist
  *
  * Description:
-- 
2.45.2