lib/os/heap: rename struct z_heap.len to struct z_heap.end_chunk

The end marker chunk was represented by the len field of struct z_heap.
It is now renamed to end_chunk to make it more obvious what it is.

And while at it...

Given that it is used in size_too_big() to cap the allocation size
already, we no longer need to test the bucket index against the
biggest index possible derived from end_chunk in alloc_chunk(). The
corresponding bucket_idx() call is relatively expensive on some
architectures so avoiding it (turning it into a CHECK() instead) is
a good thing.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

lib/os/heap-validate.c

@@ -19,7 +19,7 @@
 
 static size_t max_chunkid(struct z_heap *h)
 {
-	return h->len - min_chunk_size(h);
+	return h->end_chunk - min_chunk_size(h);
 }
 
 #define VALIDATE(cond) do { if (!(cond)) { return false; } } while (0)
@@ -28,14 +28,14 @@ static bool in_bounds(struct z_heap *h, chunkid_t c)
 {
 	VALIDATE(c >= right_chunk(h, 0));
 	VALIDATE(c <= max_chunkid(h));
-	VALIDATE(chunk_size(h, c) < h->len);
+	VALIDATE(chunk_size(h, c) < h->end_chunk);
 	return true;
 }
 
 static bool valid_chunk(struct z_heap *h, chunkid_t c)
 {
 	VALIDATE(chunk_size(h, c) > 0);
-	VALIDATE(c + chunk_size(h, c) <= h->len);
+	VALIDATE(c + chunk_size(h, c) <= h->end_chunk);
 	VALIDATE(in_bounds(h, c));
 	VALIDATE(right_chunk(h, left_chunk(h, c)) == c);
 	VALIDATE(left_chunk(h, right_chunk(h, c)) == c);
@@ -85,7 +85,7 @@ bool sys_heap_validate(struct sys_heap *heap)
 			return false;
 		}
 	}
-	if (c != h->len) {
+	if (c != h->end_chunk) {
 		return false;  /* Should have exactly consumed the buffer */
 	}
 
@@ -93,7 +93,7 @@ bool sys_heap_validate(struct sys_heap *heap)
 	 * should be correct, and all chunk entries should point into
 	 * valid unused chunks.  Mark those chunks USED, temporarily.
 	 */
-	for (int b = 0; b <= bucket_idx(h, h->len); b++) {
+	for (int b = 0; b <= bucket_idx(h, h->end_chunk); b++) {
 		chunkid_t c0 = h->buckets[b].next;
 		uint32_t n = 0;
 
@@ -137,7 +137,7 @@ bool sys_heap_validate(struct sys_heap *heap)
 
 		set_chunk_used(h, c, solo_free_header(h, c));
 	}
-	if (c != h->len) {
+	if (c != h->end_chunk) {
 		return false;  /* Should have exactly consumed the buffer */
 	}
 
@@ -145,7 +145,7 @@ bool sys_heap_validate(struct sys_heap *heap)
 	 * pass caught all the blocks and that they now show UNUSED.
 	 * Mark them USED.
 	 */
-	for (int b = 0; b <= bucket_idx(h, h->len); b++) {
+	for (int b = 0; b <= bucket_idx(h, h->end_chunk); b++) {
 		chunkid_t c0 = h->buckets[b].next;
 		int n = 0;
 
@@ -318,11 +318,11 @@ void sys_heap_stress(void *(*alloc)(void *arg, size_t bytes),
  */
 void heap_print_info(struct z_heap *h, bool dump_chunks)
 {
-	int i, nb_buckets = bucket_idx(h, h->len) + 1;
+	int i, nb_buckets = bucket_idx(h, h->end_chunk) + 1;
 	size_t free_bytes, allocated_bytes, total, overhead;
 
 	printk("Heap at %p contains %d units in %d buckets\n\n",
-	       chunk_buf(h), h->len, nb_buckets);
+	       chunk_buf(h), h->end_chunk, nb_buckets);
 
 	printk("  bucket#    min units        total      largest      largest\n"
 	       "             threshold       chunks      (units)      (bytes)\n"
@@ -352,7 +352,7 @@ void heap_print_info(struct z_heap *h, bool dump_chunks)
 	}
 	free_bytes = allocated_bytes = 0;
 	for (chunkid_t c = 0; ; c = right_chunk(h, c)) {
-		if (c == 0 || c == h->len) {
+		if (c == 0 || c == h->end_chunk) {
 			/* those are always allocated for internal purposes */
 		} else if (chunk_used(h, c)) {
 			allocated_bytes += chunk_size(h, c) * CHUNK_UNIT
@@ -371,16 +371,13 @@ void heap_print_info(struct z_heap *h, bool dump_chunks)
 			       left_chunk(h, c),
 			       right_chunk(h, c));
 		}
-		if (c == h->len) {
+		if (c == h->end_chunk) {
 			break;
 		}
 	}
 
-	/*
+	/* The end marker chunk has a header. It is part of the overhead. */
-	 * The final chunk at h->len  is just a header serving as a end
+	total = h->end_chunk * CHUNK_UNIT + chunk_header_bytes(h);
-	 * marker. It is part of the overhead.
-	 */
-	total = h->len * CHUNK_UNIT + chunk_header_bytes(h);
 	overhead = total - free_bytes - allocated_bytes;
 	printk("\n%zd free bytes, %zd allocated bytes, overhead = %zd bytes (%zd.%zd%%)\n",
 	       free_bytes, allocated_bytes, overhead,

lib/os/heap.c

@@ -172,9 +172,7 @@ static chunkid_t alloc_chunk(struct z_heap *h, size_t sz)
 	int bi = bucket_idx(h, sz);
 	struct z_heap_bucket *b = &h->buckets[bi];
 
-	if (bi > bucket_idx(h, h->len)) {
+	CHECK(bi <= bucket_idx(h, h->end_chunk));
-		return 0;
-	}
 
 	/* First try a bounded count of items from the minimal bucket
 	 * size.  These may not fit, trying (e.g.) three means that
@@ -383,7 +381,7 @@ void sys_heap_init(struct sys_heap *heap, void *mem, size_t bytes)
 	/* Must fit in a 31 bit count of HUNK_UNIT */
 	__ASSERT(bytes / CHUNK_UNIT <= 0x7fffffffU, "heap size is too big");
 
-	/* Reserve the final marker chunk's header */
+	/* Reserve the end marker chunk's header */
 	__ASSERT(bytes > heap_footer_bytes(bytes), "heap size is too small");
 	bytes -= heap_footer_bytes(bytes);
 
@@ -398,7 +396,7 @@ void sys_heap_init(struct sys_heap *heap, void *mem, size_t bytes)
 	struct z_heap *h = (struct z_heap *)addr;
 	heap->heap = h;
 	h->chunk0_hdr_area = 0;
-	h->len = buf_sz;
+	h->end_chunk = buf_sz;
 	h->avail_buckets = 0;
 
 	int nb_buckets = bucket_idx(h, buf_sz) + 1;

lib/os/heap.h

@@ -64,7 +64,7 @@ struct z_heap_bucket {
 
 struct z_heap {
 	uint64_t chunk0_hdr_area;  /* matches the largest header */
-	uint32_t len;
+	chunkid_t end_chunk;
 	uint32_t avail_buckets;
 	struct z_heap_bucket buckets[0];
 };
@@ -81,7 +81,7 @@ static inline bool big_heap_bytes(size_t bytes)
 
 static inline bool big_heap(struct z_heap *h)
 {
-	return big_heap_chunks(h->len);
+	return big_heap_chunks(h->end_chunk);
 }
 
 static inline chunk_unit_t *chunk_buf(struct z_heap *h)
@@ -106,7 +106,7 @@ static inline size_t chunk_field(struct z_heap *h, chunkid_t c,
 static inline void chunk_set(struct z_heap *h, chunkid_t c,
 			     enum chunk_fields f, chunkid_t val)
 {
-	CHECK(c <= h->len);
+	CHECK(c <= h->end_chunk);
 
 	chunk_unit_t *buf = chunk_buf(h);
 	void *cmem = &buf[c];
@@ -239,9 +239,8 @@ static inline bool size_too_big(struct z_heap *h, size_t bytes)
 	/*
 	 * Quick check to bail out early if size is too big.
 	 * Also guards against potential arithmetic overflows elsewhere.
-	 * There is a minimum of one chunk always in use by the heap header.
 	 */
-	return (bytes / CHUNK_UNIT) >= h->len;
+	return (bytes / CHUNK_UNIT) >= h->end_chunk;
 }
 
 /* For debugging */