Change default block size alignment to be 4 for memory saving on 32-bit arch
For a 32-bit userspace, `struct LinkedListEntry` takes 8 bytes for
storing the two pointers, a default block allocator size alignment of
16-bytes would waste 50% of memory. By changing the alignment to size
of a pointer, it saves >1MB memory postboot on wembley device.
Bug: http://b/206889551
Test: bionic-unit-tests
Change-Id: Ie92399c9bb3971f631396ee09bbbfd7eb17dc1a7
diff --git a/linker/linker_block_allocator.cpp b/linker/linker_block_allocator.cpp
index 5b68b1d..60e5e1c 100644
--- a/linker/linker_block_allocator.cpp
+++ b/linker/linker_block_allocator.cpp
@@ -31,6 +31,7 @@
#include <inttypes.h>
#include <string.h>
#include <sys/mman.h>
+#include <sys/param.h>
#include <sys/prctl.h>
#include <unistd.h>
@@ -39,11 +40,6 @@
static constexpr size_t kAllocateSize = PAGE_SIZE * 100;
static_assert(kAllocateSize % PAGE_SIZE == 0, "Invalid kAllocateSize.");
-// the multiplier should be power of 2
-static constexpr size_t round_up(size_t size, size_t multiplier) {
- return (size + (multiplier - 1)) & ~(multiplier-1);
-}
-
struct LinkerBlockAllocatorPage {
LinkerBlockAllocatorPage* next;
uint8_t bytes[kAllocateSize - 16] __attribute__((aligned(16)));
@@ -54,13 +50,14 @@
size_t num_free_blocks;
};
+static_assert(kBlockSizeAlign >= alignof(FreeBlockInfo));
+static_assert(kBlockSizeMin == sizeof(FreeBlockInfo));
+
LinkerBlockAllocator::LinkerBlockAllocator(size_t block_size)
- : block_size_(
- round_up(block_size < sizeof(FreeBlockInfo) ? sizeof(FreeBlockInfo) : block_size, 16)),
- page_list_(nullptr),
- free_block_list_(nullptr),
- allocated_(0)
-{}
+ : block_size_(__BIONIC_ALIGN(MAX(block_size, kBlockSizeMin), kBlockSizeAlign)),
+ page_list_(nullptr),
+ free_block_list_(nullptr),
+ allocated_(0) {}
void* LinkerBlockAllocator::alloc() {
if (free_block_list_ == nullptr) {
diff --git a/linker/linker_block_allocator.h b/linker/linker_block_allocator.h
index 8ae4094..32656c7 100644
--- a/linker/linker_block_allocator.h
+++ b/linker/linker_block_allocator.h
@@ -33,6 +33,9 @@
#include <android-base/macros.h>
+static constexpr size_t kBlockSizeAlign = sizeof(void*);
+static constexpr size_t kBlockSizeMin = sizeof(void*) * 2;
+
struct LinkerBlockAllocatorPage;
/*
diff --git a/linker/linker_block_allocator_test.cpp b/linker/linker_block_allocator_test.cpp
index 6fb2b26..56fbee8 100644
--- a/linker/linker_block_allocator_test.cpp
+++ b/linker/linker_block_allocator_test.cpp
@@ -29,6 +29,7 @@
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
+#include <sys/param.h>
#include <gtest/gtest.h>
@@ -44,12 +45,16 @@
};
/*
- * this one has size below allocator cap which is 2*sizeof(void*)
+ * this one has size below kBlockSizeAlign
*/
struct test_struct_small {
- char str[5];
+ char str[3];
};
+struct test_struct_max_align {
+ char str[16];
+} __attribute__((aligned(16)));
+
/*
* 1009 byte struct (1009 is prime)
*/
@@ -58,54 +63,49 @@
};
static size_t kPageSize = sysconf(_SC_PAGE_SIZE);
-};
-TEST(linker_allocator, test_nominal) {
- LinkerTypeAllocator<test_struct_nominal> allocator;
+template <typename Element>
+void linker_allocator_test_helper() {
+ LinkerTypeAllocator<Element> allocator;
- test_struct_nominal* ptr1 = allocator.alloc();
+ Element* ptr1 = allocator.alloc();
ASSERT_TRUE(ptr1 != nullptr);
- ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr1) % 16);
- test_struct_nominal* ptr2 = allocator.alloc();
- ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr2) % 16);
+ ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr1) % kBlockSizeAlign);
+ ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr1) % alignof(Element));
+ Element* ptr2 = allocator.alloc();
+ ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr2) % kBlockSizeAlign);
+ ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr2) % alignof(Element));
ASSERT_TRUE(ptr2 != nullptr);
- // they should be next to each other.
- ASSERT_EQ(reinterpret_cast<uint8_t*>(ptr1)+16, reinterpret_cast<uint8_t*>(ptr2));
- ptr1->value = 42;
+ // they should be next to each other.
+ size_t dist = __BIONIC_ALIGN(MAX(sizeof(Element), kBlockSizeMin), kBlockSizeAlign);
+ ASSERT_EQ(reinterpret_cast<uint8_t*>(ptr1) + dist, reinterpret_cast<uint8_t*>(ptr2));
allocator.free(ptr1);
allocator.free(ptr2);
}
+}; // anonymous namespace
+
+TEST(linker_allocator, test_nominal) {
+ linker_allocator_test_helper<test_struct_nominal>();
+}
+
TEST(linker_allocator, test_small) {
- LinkerTypeAllocator<test_struct_small> allocator;
+ linker_allocator_test_helper<test_struct_small>();
+}
- char* ptr1 = reinterpret_cast<char*>(allocator.alloc());
- char* ptr2 = reinterpret_cast<char*>(allocator.alloc());
-
- ASSERT_TRUE(ptr1 != nullptr);
- ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr1) % 16);
- ASSERT_TRUE(ptr2 != nullptr);
- ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr2) % 16);
- ASSERT_EQ(ptr1+16, ptr2); // aligned to 16
+TEST(linker_allocator, test_max_align) {
+ linker_allocator_test_helper<test_struct_max_align>();
}
TEST(linker_allocator, test_larger) {
+ linker_allocator_test_helper<test_struct_larger>();
+
LinkerTypeAllocator<test_struct_larger> allocator;
- test_struct_larger* ptr1 = allocator.alloc();
- test_struct_larger* ptr2 = allocator.alloc();
-
- ASSERT_TRUE(ptr1 != nullptr);
- ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr1) % 16);
- ASSERT_TRUE(ptr2 != nullptr);
- ASSERT_EQ(0U, reinterpret_cast<uintptr_t>(ptr2) % 16);
-
- ASSERT_EQ(reinterpret_cast<uint8_t*>(ptr1) + 1024, reinterpret_cast<uint8_t*>(ptr2));
-
// lets allocate until we reach next page.
- size_t n = kPageSize/sizeof(test_struct_larger) + 1 - 2;
+ size_t n = kPageSize / sizeof(test_struct_larger) + 1;
for (size_t i=0; i<n; ++i) {
ASSERT_TRUE(allocator.alloc() != nullptr);
@@ -113,7 +113,6 @@
test_struct_larger* ptr_to_free = allocator.alloc();
ASSERT_TRUE(ptr_to_free != nullptr);
- allocator.free(ptr1);
}
static void protect_all() {