[PATCH v2 1/4] mm/slub: use a track count for user metadata sizing

[Pengpeng Hou]

SLAB_STORE_USER metadata consists of allocation and free tracks, but the
object-layout calculations repeat the literal count at each offset site.

Add TRACK_NR to the existing track-item enum and use it for metadata
initialization, original-size placement, object-extension offsets, padding
checks and cache sizing.  This is a behavior-preserving preparation for
extending the tracked history.

Assisted-by: Codex:gpt-5
Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
 mm/slub.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 0337e60db5ac..0653def0fe36 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -329,7 +329,7 @@ struct track {
 	unsigned long when;	/* When did the operation occur */
 };
 
-enum track_item { TRACK_ALLOC, TRACK_FREE };
+enum track_item { TRACK_ALLOC, TRACK_FREE, TRACK_NR };
 
 #ifdef SLAB_SUPPORTS_SYSFS
 static int sysfs_slab_add(struct kmem_cache *);
@@ -753,7 +753,7 @@ static inline void set_orig_size(struct kmem_cache *s,
 		return;
 
 	p += get_info_end(s);
-	p += sizeof(struct track) * 2;
+	p += sizeof(struct track) * TRACK_NR;
 
 	*(unsigned long *)p = orig_size;
 }
@@ -769,7 +769,7 @@ static inline unsigned long get_orig_size(struct kmem_cache *s, void *object)
 		return s->object_size;
 
 	p += get_info_end(s);
-	p += sizeof(struct track) * 2;
+	p += sizeof(struct track) * TRACK_NR;
 
 	return *(unsigned long *)p;
 }
@@ -887,7 +887,7 @@ static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)
 	unsigned int offset = get_info_end(s);
 
 	if (kmem_cache_debug_flags(s, SLAB_STORE_USER))
-		offset += sizeof(struct track) * 2;
+		offset += sizeof(struct track) * TRACK_NR;
 
 	if (slub_debug_orig_size(s))
 		offset += sizeof(unsigned long);
@@ -1090,7 +1090,7 @@ static void init_tracking(struct kmem_cache *s, void *object)
 		return;
 
 	p = get_track(s, object, TRACK_ALLOC);
-	memset(p, 0, 2*sizeof(struct track));
+	memset(p, 0, sizeof(struct track) * TRACK_NR);
 }
 
 static void print_track(const char *s, struct track *t, unsigned long pr_time)
@@ -1199,7 +1199,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
 	off = get_info_end(s);
 
 	if (s->flags & SLAB_STORE_USER)
-		off += 2 * sizeof(struct track);
+		off += sizeof(struct track) * TRACK_NR;
 
 	if (slub_debug_orig_size(s))
 		off += sizeof(unsigned long);
@@ -1403,7 +1403,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
 
 	if (s->flags & SLAB_STORE_USER) {
 		/* We also have user information there */
-		off += 2 * sizeof(struct track);
+		off += sizeof(struct track) * TRACK_NR;
 
 		if (s->flags & SLAB_KMALLOC)
 			off += sizeof(unsigned long);
@@ -7895,7 +7895,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
 		 * Need to store information about allocs and frees after
 		 * the object.
 		 */
-		size += 2 * sizeof(struct track);
+		size += sizeof(struct track) * TRACK_NR;
 
 		/* Save the original kmalloc request size */
 		if (flags & SLAB_KMALLOC)
-- 
2.50.1 (Apple Git-155)