small: improve real_size calculation in small_alloc_info

include/small/small.h

@@ -211,36 +211,6 @@ smalloc(struct small_alloc *alloc, size_t size);
 void
 smfree(struct small_alloc *alloc, void *ptr, size_t size);
 
-/**
- * @brief Return an unique index associated with a chunk allocated
- * by the allocator.
- *
- * This index space is more dense than the pointers space,
- * especially in the least significant bits.  This number is
- * needed because some types of box's indexes (e.g. BITSET) have
- * better performance then they operate on sequential offsets
- * (i.e. dense space) instead of memory pointers (sparse space).
- *
- * The calculation is based on SLAB number and the position of an
- * item within it. Current implementation only guarantees that
- * adjacent chunks from one SLAB will have consecutive indexes.
- * That is, if two chunks were sequentially allocated from one
- * chunk they will have sequential ids. If a second chunk was
- * allocated from another SLAB thеn the difference between indexes
- * may be more than one.
- *
- * @param ptr pointer to memory allocated in small_alloc
- * @return unique index
- */
-size_t
-small_ptr_compress(struct small_alloc *alloc, void *ptr);
-
-/**
- * Perform the opposite action of small_ptr_compress().
- */
-void *
-small_ptr_decompress(struct small_alloc *alloc, size_t val);
-
 void
 small_stats(struct small_alloc *alloc,
 	    struct small_stats *totals,
@@ -255,8 +225,6 @@ small_alloc_check(struct small_alloc *alloc)
 /**
  * Fill `info' with the information about allocation `ptr' of size `size'.
  * See `struct small_alloc_info' for the description of each field.
- * Note that this function can return different `info->real_size' for the same
- * input, depending on the current `small_mempool->used_pool'.
  */
 void
 small_alloc_info(struct small_alloc *alloc, void *ptr, size_t size,

small/small.c

@@ -468,12 +468,14 @@ void
 small_alloc_info(struct small_alloc *alloc, void *ptr, size_t size,
 		 struct small_alloc_info *info)
 {
-	(void)ptr;
 	struct small_mempool *small_mempool = small_mempool_search(alloc, size);
 	info->is_large = small_mempool == NULL;
-	if (info->is_large)
+	if (info->is_large) {
 		info->real_size = size;
-	else
-		info->real_size = small_mempool->used_pool->pool.objsize;
+	} else {
+		struct mslab *mslab = (struct mslab *)
+			slab_from_ptr(ptr, small_mempool->pool.slab_ptr_mask);
+		info->real_size = mslab->mempool->objsize;
+	}
 	assert(info->real_size >= size);
 }

test/small_alloc.c

@@ -141,8 +141,10 @@ static inline void
 check_small_alloc_info(struct small_alloc *alloc, size_t size, bool is_large,
 		       size_t real_size)
 {
+	void *ptr = smalloc(alloc, size);
 	struct small_alloc_info info;
-	small_alloc_info(alloc, NULL, size, &info);
+	small_alloc_info(alloc, ptr, size, &info);
+	smfree(alloc, ptr, size);
 	fail_unless(info.is_large == is_large);
 	fail_unless(info.real_size == real_size);
 }
@@ -185,6 +187,48 @@ test_small_alloc_info(void)
 	check_plan();
 }
 
+/**
+ * Make sure `info.real_size' is calculated correctly.
+ * See https://github.com/tarantool/tarantool/issues/10217
+ */
+static void
+test_small_alloc_info_gh_10217(void)
+{
+	plan(1);
+	header();
+	/*
+	 * One of the mempool groups consists of two mempools with objsizes
+	 * 3072 and 4096. The largest objsize in the previous group is 2048.
+	 */
+	float actual_alloc_factor;
+	small_alloc_create(&alloc, &cache, 64, 64, 1.5f, &actual_alloc_factor);
+
+	const size_t size = 2240;
+	const size_t count = 200;
+	struct small_alloc_info info;
+
+	for (size_t i = 0; i < count; i++) {
+		ptrs[i] = smalloc(&alloc, size);
+		small_alloc_info(&alloc, ptrs[i], size, &info);
+		fail_unless(info.real_size == (i > 127 ? 3072 : 4096));
+	}
+	/*
+	 * Check that all "real sizes" are still correct after `used_pool' was
+	 * switched.
+	 */
+	for (size_t i = 0; i < count; i++) {
+		small_alloc_info(&alloc, ptrs[i], size, &info);
+		fail_unless(info.real_size == (i > 127 ? 3072 : 4096));
+	}
+	ok(true);
+
+	for (size_t i = 0; i < count; i++)
+		smfree(&alloc, ptrs[i], size);
+	small_alloc_destroy(&alloc);
+	footer();
+	check_plan();
+}
+
 /**
  * Make sure allocator works with low alloc_factor and high memory
  * pressure.
@@ -317,7 +361,7 @@ int main()
 #ifdef ENABLE_ASAN
 	plan(3);
 #else
-	plan(4);
+	plan(5);
 #endif
 	header();
 
@@ -334,6 +378,7 @@ int main()
 #ifndef ENABLE_ASAN
 	small_alloc_large();
 	test_small_alloc_info();
+	test_small_alloc_info_gh_10217();
 	small_alloc_low_alloc_factor();
 #else
 	small_wrong_size_in_free();