[Tarantool-patches] [PATCH small 2/2] lsregion: provide aligned version of alloc

[Vladislav Shpilevoy]

lsregion_alloc() can return an address, even odd. This is not
good when the allocation is going to be used for a type, which
requires alignment, such as a number, or a struct having numbers
in it.

Unaligned access to objects saved into the returned memory is
either slower than aligned access, or can even lead to a crash on
certain architectures. Also it makes 'alignment' clang sanitizer
crazy.

The patch provides a function to make aligned allocations on
lsregion.

Part of https://github.com/tarantool/tarantool/issues/4609
---
 small/lsregion.h | 37 ++++++++++++++++++++++++++++++++----
 test/lsregion.c  | 49 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 81 insertions(+), 5 deletions(-)

diff --git a/small/lsregion.h b/small/lsregion.h
index 52431e7..b4212b3 100644
--- a/small/lsregion.h
+++ b/small/lsregion.h
@@ -127,6 +127,18 @@ lslab_unused(const struct lslab *slab)
 	return slab->slab_size - slab->slab_used;
 }
 
+/**
+ * Update slab statistics and meta according to new allocation.
+ */
+static inline void
+lslab_use(struct lslab *slab, size_t size, int64_t id)
+{
+	assert(size <= lslab_unused(slab));
+	assert(slab->max_id <= id);
+	slab->slab_used += size;
+	slab->max_id = id;
+}
+
 /**
  * Pointer to the end of the used part of the slab.
  * @param slab Slab container.
@@ -199,10 +211,27 @@ lsregion_alloc(struct lsregion *lsregion, size_t size, int64_t id)
 		return NULL;
 	struct lslab *slab = rlist_last_entry(&lsregion->slabs.slabs,
 					      struct lslab, next_in_list);
-	assert(size <= lslab_unused(slab));
-	assert(slab->max_id <= id);
-	slab->slab_used += size;
-	slab->max_id = id;
+	lslab_use(slab, size, id);
+	lsregion->slabs.stats.used += size;
+	return res;
+}
+
+/**
+ * The same as normal alloc, but the resulting pointer is aligned
+ * by @a alignment.
+ */
+static inline void *
+lsregion_aligned_alloc(struct lsregion *lsregion, size_t size, size_t alignment,
+		       int64_t id)
+{
+	void *unaligned = lsregion_reserve(lsregion, size + alignment - 1);
+	if (unaligned == NULL)
+		return NULL;
+	void *res = (void *)small_align((uintptr_t)unaligned, alignment);
+	struct lslab *slab = rlist_last_entry(&lsregion->slabs.slabs,
+					      struct lslab, next_in_list);
+	size += res - unaligned;
+	lslab_use(slab, size, id);
 	lsregion->slabs.stats.used += size;
 	return res;
 }
diff --git a/test/lsregion.c b/test/lsregion.c
index 8a8ff56..0232f8a 100644
--- a/test/lsregion.c
+++ b/test/lsregion.c
@@ -396,16 +396,63 @@ test_reserve(void)
 	check_plan();
 }
 
+static void
+test_aligned(void)
+{
+	plan(11);
+	header();
+
+	struct quota quota;
+	struct slab_arena arena;
+	struct lsregion allocator;
+	quota_init(&quota, 16 * SLAB_MIN_SIZE);
+	is(slab_arena_create(&arena, &quota, 0, 0, MAP_PRIVATE), 0, "init");
+	lsregion_create(&allocator, &arena);
+	int id = 0;
+
+	++id;
+	void *p1 = lsregion_aligned_alloc(&allocator, 8, 8, id);
+	ok((unsigned long)p1 % 8 == 0, "trivial aligned");
+	is(lsregion_used(&allocator), 8, "'used'");
+
+	++id;
+	void *p2 = lsregion_aligned_alloc(&allocator, 1, 16, id);
+	ok((unsigned long)p2 % 16 == 0, "16 byte alignment for 1 byte");
+	void *p3 = lsregion_aligned_alloc(&allocator, 1, 16, id);
+	ok(p3 == (char *)p2 + 16, "second 16 aligned alloc of 1 byte is far "
+	   "from first");
+	ok((unsigned long)p3 % 16 == 0, "aligned by 16 too");
+
+	is(lsregion_used(&allocator), (size_t)(p3 + 1 - p1), "'used'");
+
+	++id;
+	void *p4 = lsregion_aligned_alloc(&allocator, 3, 4, id);
+	ok(p4 == (char *)p3 + 4, "align next by 4 bytes, should be closer to "
+	   "previous");
+	ok((unsigned long)p4 % 4 == 0, "aligned by 4");
+	is(lsregion_used(&allocator), (size_t)(p4 + 3 - p1), "'used'");
+
+	lsregion_gc(&allocator, id);
+	is(lsregion_used(&allocator), 0, "gc deleted all");
+
+	lsregion_destroy(&allocator);
+	slab_arena_destroy(&arena);
+
+	footer();
+	check_plan();
+}
+
 int
 main()
 {
-	plan(5);
+	plan(6);
 
 	test_basic();
 	test_many_allocs_one_slab();
 	test_many_allocs_many_slabs();
 	test_big_data_small_slabs();
 	test_reserve();
+	test_aligned();
 
 	return check_plan();
 }
-- 
2.21.1 (Apple Git-122.3)