mirror of
https://github.com/LadybirdBrowser/ladybird.git
synced 2024-09-21 18:37:58 +03:00
LibC: Implement a simple freelist-based malloc() with size classes.
It's not thread-safe yet, and there is lots of room for improvement. Still it's a lot faster than the first-fit bitmap-based one it replaces.
This commit is contained in:
Andreas Kling
parent
d3bd4fdcfe
commit
4291e96991
Notes:
sideshowbarker
2024-07-19 14:22:18 +09:00
Author: https://github.com/awesomekling Commit: https://github.com/SerenityOS/serenity/commit/4291e969915
@ -17,6 +17,7 @@ LIBC_OBJS = \
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strings.o \
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mman.o \
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dirent.o \
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malloc.o \
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stdlib.o \
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time.o \
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utsname.o \
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@ -84,4 +85,4 @@ install: $(LIBRARY)
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cp $(LIBRARY) ../Base/usr/lib
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cp crt0.o ../Base/usr/lib/
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cp crti.ao ../Base/usr/lib/crti.o
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cp crtn.ao ../Base/usr/lib/crtn.o
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cp crtn.ao ../Base/usr/lib/crtn.o
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228
LibC/malloc.cpp
Normal file
228
LibC/malloc.cpp
Normal file
@ -0,0 +1,228 @@
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#include <AK/Bitmap.h>
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#include <AK/InlineLinkedList.h>
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#include <sys/mman.h>
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#include <stdlib.h>
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#include <assert.h>
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#include <stdio.h>
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#include <serenity.h>
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// FIXME: Thread safety.
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//#define MALLOC_DEBUG
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#define MALLOC_SCRUB_BYTE 0x85
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#define FREE_SCRUB_BYTE 0x82
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#define MAGIC_PAGE_HEADER 0x42657274
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#define MAGIC_BIGALLOC_HEADER 0x42697267
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#define PAGE_ROUND_UP(x) ((((size_t)(x)) + PAGE_SIZE-1) & (~(PAGE_SIZE-1)))
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static bool s_log_malloc = false;
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static bool s_scrub_malloc = true;
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static bool s_scrub_free = true;
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static unsigned short size_classes[] = { 8, 16, 32, 64, 128, 252, 508, 1016, 2036, 0 };
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static constexpr size_t num_size_classes = sizeof(size_classes) / sizeof(unsigned short);
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struct CommonHeader {
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size_t m_magic;
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size_t m_size;
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};
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struct BigAllocationBlock : public CommonHeader {
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BigAllocationBlock(size_t size)
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{
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m_magic = MAGIC_BIGALLOC_HEADER;
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m_size = size;
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}
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unsigned char* m_slot[0];
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};
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struct FreelistEntry {
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FreelistEntry* next;
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};
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struct ChunkedBlock : public CommonHeader, public InlineLinkedListNode<ChunkedBlock> {
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ChunkedBlock(size_t bytes_per_chunk)
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{
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m_magic = MAGIC_PAGE_HEADER;
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m_size = bytes_per_chunk;
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m_free_chunks = chunk_capacity();
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m_freelist = (FreelistEntry*)chunk(0);
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for (size_t i = 0; i < chunk_capacity(); ++i) {
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auto* entry = (FreelistEntry*)chunk(i);
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if (i != chunk_capacity() - 1)
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entry->next = (FreelistEntry*)chunk(i + 1);
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else
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entry->next = nullptr;
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}
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}
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ChunkedBlock* m_prev { nullptr };
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ChunkedBlock* m_next { nullptr };
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FreelistEntry* m_freelist { nullptr };
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unsigned short m_free_chunks { 0 };
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unsigned char m_slot[0];
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void* chunk(int index)
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{
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return &m_slot[index * m_size];
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}
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size_t bytes_per_chunk() const { return m_size; }
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size_t free_chunks() const { return m_free_chunks; }
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size_t used_chunks() const { return chunk_capacity() - m_free_chunks; }
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size_t chunk_capacity() const { return (PAGE_SIZE - sizeof(ChunkedBlock)) / m_size; }
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};
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static InlineLinkedList<ChunkedBlock> g_allocators[num_size_classes];
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static InlineLinkedList<ChunkedBlock>* allocator_for_size(size_t size, size_t& good_size)
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{
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for (int i = 0; size_classes[i]; ++i) {
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if (size <= size_classes[i]) {
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good_size = size_classes[i];
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return &g_allocators[i];
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}
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}
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good_size = PAGE_ROUND_UP(size);
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return nullptr;
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}
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extern "C" {
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size_t malloc_good_size(size_t size)
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{
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for (int i = 0; size_classes[i]; ++i) {
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if (size < size_classes[i])
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return size_classes[i];
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}
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return PAGE_ROUND_UP(size);
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}
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static void* os_alloc(size_t size)
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{
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return mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
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}
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static void os_free(void* ptr, size_t size)
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{
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int rc = munmap(ptr, size);
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assert(rc == 0);
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}
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void* malloc(size_t size)
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{
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if (s_log_malloc)
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dbgprintf("LibC: malloc(%u)\n", size);
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if (!size)
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return nullptr;
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size_t good_size;
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auto* allocator = allocator_for_size(size, good_size);
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if (!allocator) {
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size_t real_size = sizeof(BigAllocationBlock) + size;
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void* page_ptr = os_alloc(real_size);
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BigAllocationBlock* bigalloc_header = new (page_ptr) BigAllocationBlock(real_size);
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return &bigalloc_header->m_slot[0];
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}
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assert(allocator);
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ChunkedBlock* block = nullptr;
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for (block = allocator->head(); block; block = block->next()) {
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if (block->free_chunks())
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break;
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}
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if (!block) {
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block = (ChunkedBlock*)os_alloc(PAGE_SIZE);
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char buffer[64];
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snprintf(buffer, sizeof(buffer), "malloc() page (%u)", good_size);
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set_mmap_name(block, PAGE_SIZE, buffer);
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new (block) ChunkedBlock(good_size);
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allocator->append(block);
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}
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--block->m_free_chunks;
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void* ptr = block->m_freelist;
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block->m_freelist = block->m_freelist->next;
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#ifdef MALLOC_DEBUG
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dbgprintf("LibC: allocated %p (chunk %d in allocator %p, size %u)\n", ptr, index, page, page->bytes_per_chunk());
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#endif
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if (s_scrub_malloc)
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memset(ptr, MALLOC_SCRUB_BYTE, block->m_size);
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return ptr;
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ASSERT_NOT_REACHED();
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}
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void free(void* ptr)
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{
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if (!ptr)
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return;
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void* page_base = (void*)((uintptr_t)ptr & (uintptr_t)~0xfff);
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size_t magic = *(size_t*)page_base;
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if (magic == MAGIC_BIGALLOC_HEADER) {
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auto* header = (BigAllocationBlock*)page_base;
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os_free(header, header->m_size);
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return;
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}
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assert(magic == MAGIC_PAGE_HEADER);
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auto* page = (ChunkedBlock*)page_base;
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#ifdef MALLOC_DEBUG
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dbgprintf("LibC: freeing %p in allocator %p (size=%u, used=%u)\n", ptr, page, page->bytes_per_chunk(), page->used_chunks());
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#endif
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if (s_scrub_free)
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memset(ptr, FREE_SCRUB_BYTE, page->bytes_per_chunk());
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auto* entry = (FreelistEntry*)ptr;
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entry->next = page->m_freelist;
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page->m_freelist = entry;
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++page->m_free_chunks;
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}
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void* calloc(size_t count, size_t size)
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{
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size_t new_size = count * size;
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auto* ptr = malloc(new_size);
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memset(ptr, 0, new_size);
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return ptr;
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}
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void* realloc(void* ptr, size_t size)
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{
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if (!ptr)
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return malloc(size);
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size_t old_size = 0;
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void* page_base = (void*)((uintptr_t)ptr & (uintptr_t)~0xfff);
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auto* header = (const CommonHeader*)page_base;
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old_size = header->m_size;
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if (size == old_size)
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return ptr;
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auto* new_ptr = malloc(size);
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memcpy(new_ptr, ptr, min(old_size, size));
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free(ptr);
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return new_ptr;
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}
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void __malloc_init()
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{
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if (getenv("LIBC_NOSCRUB_MALLOC"))
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s_scrub_malloc = false;
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if (getenv("LIBC_NOSCRUB_FREE"))
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s_scrub_free = false;
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if (getenv("LIBC_LOG_MALLOC"))
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s_log_malloc = true;
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}
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}
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172
LibC/stdlib.cpp
172
LibC/stdlib.cpp
@ -16,178 +16,6 @@
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extern "C" {
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#define MALLOC_SCRUB_BYTE 0x85
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#define FREE_SCRUB_BYTE 0x82
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struct MallocHeader {
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uint16_t first_chunk_index;
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uint16_t chunk_count : 15;
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bool is_mmap : 1;
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size_t size;
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};
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#define CHUNK_SIZE 32
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#define POOL_SIZE 4 * 1048576
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static const size_t malloc_budget = POOL_SIZE;
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static byte s_malloc_map[POOL_SIZE / CHUNK_SIZE / 8];
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static byte* s_malloc_pool;
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static uint32_t s_malloc_sum_alloc = 0;
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static uint32_t s_malloc_sum_free = POOL_SIZE;
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static bool s_log_malloc = false;
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static bool s_scrub_malloc = true;
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static bool s_scrub_free = true;
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void* malloc(size_t size)
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{
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if (s_log_malloc)
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dbgprintf("LibC: malloc(%u)\n", size);
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if (size == 0)
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return nullptr;
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// We need space for the MallocHeader structure at the head of the block.
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size_t real_size = size + sizeof(MallocHeader);
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if (real_size >= PAGE_SIZE) {
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auto* memory = mmap(nullptr, real_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
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if (memory == MAP_FAILED) {
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fprintf(stderr, "malloc() failed to mmap() for a %u-byte allocation: %s", size, strerror(errno));
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volatile char* crashme = (char*)0xf007d00d;
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*crashme = 0;
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return nullptr;
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}
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auto* header = (MallocHeader*)(memory);
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byte* ptr = ((byte*)header) + sizeof(MallocHeader);
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header->chunk_count = 0;
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header->first_chunk_index = 0;
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header->size = real_size;
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header->is_mmap = true;
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return ptr;
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}
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if (s_malloc_sum_free < real_size) {
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fprintf(stderr, "malloc(): Out of memory\ns_malloc_sum_free=%u, real_size=%u\n", s_malloc_sum_free, real_size);
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ASSERT_NOT_REACHED();
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}
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size_t chunks_needed = real_size / CHUNK_SIZE;
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if (real_size % CHUNK_SIZE)
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chunks_needed++;
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size_t chunks_here = 0;
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size_t first_chunk = 0;
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for (unsigned i = 0; i < (POOL_SIZE / CHUNK_SIZE / 8); ++i) {
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if (s_malloc_map[i] == 0xff) {
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// Skip over completely full bucket.
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chunks_here = 0;
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continue;
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}
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// FIXME: This scan can be optimized further with TZCNT.
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for (unsigned j = 0; j < 8; ++j) {
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if ((s_malloc_map[i] & (1<<j))) {
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// This is in use, so restart chunks_here counter.
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chunks_here = 0;
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continue;
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}
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if (chunks_here == 0) {
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// Mark where potential allocation starts.
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first_chunk = i * 8 + j;
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}
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++chunks_here;
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if (chunks_here == chunks_needed) {
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auto* header = (MallocHeader*)(s_malloc_pool + (first_chunk * CHUNK_SIZE));
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byte* ptr = ((byte*)header) + sizeof(MallocHeader);
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header->chunk_count = chunks_needed;
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header->first_chunk_index = first_chunk;
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header->is_mmap = false;
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header->size = size;
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for (size_t k = first_chunk; k < (first_chunk + chunks_needed); ++k)
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s_malloc_map[k / 8] |= 1 << (k % 8);
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s_malloc_sum_alloc += header->chunk_count * CHUNK_SIZE;
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s_malloc_sum_free -= header->chunk_count * CHUNK_SIZE;
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if (s_scrub_malloc)
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memset(ptr, MALLOC_SCRUB_BYTE, (header->chunk_count * CHUNK_SIZE) - sizeof(MallocHeader));
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return ptr;
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}
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}
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}
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fprintf(stderr, "malloc(): Out of memory (no consecutive chunks found for size %u)\n", size);
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volatile char* crashme = (char*)0xc007d00d;
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*crashme = 0;
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return nullptr;
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}
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void free(void* ptr)
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{
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if (!ptr)
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return;
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auto* header = (MallocHeader*)((((byte*)ptr) - sizeof(MallocHeader)));
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if (header->is_mmap) {
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int rc = munmap(header, header->size);
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if (rc < 0)
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fprintf(stderr, "free(): munmap(%p) for allocation %p with size %u failed: %s\n", header, ptr, header->size, strerror(errno));
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return;
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}
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for (int i = header->first_chunk_index; i < (header->first_chunk_index + header->chunk_count); ++i)
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s_malloc_map[i / 8] &= ~(1 << (i % 8));
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s_malloc_sum_alloc -= header->chunk_count * CHUNK_SIZE;
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s_malloc_sum_free += header->chunk_count * CHUNK_SIZE;
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if (s_scrub_free)
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memset(header, FREE_SCRUB_BYTE, header->chunk_count * CHUNK_SIZE);
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}
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void __malloc_init()
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{
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s_malloc_pool = (byte*)mmap(nullptr, malloc_budget, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
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int rc = set_mmap_name(s_malloc_pool, malloc_budget, "malloc pool");
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if (rc < 0)
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perror("set_mmap_name failed");
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if (getenv("LIBC_NOSCRUB_MALLOC"))
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s_scrub_malloc = false;
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if (getenv("LIBC_NOSCRUB_FREE"))
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s_scrub_free = false;
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if (getenv("LIBC_LOG_MALLOC"))
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s_log_malloc = true;
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}
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void* calloc(size_t count, size_t size)
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{
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size_t new_size = count * size;
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auto* ptr = malloc(new_size);
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memset(ptr, 0, new_size);
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return ptr;
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}
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void* realloc(void *ptr, size_t size)
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{
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if (!ptr)
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return malloc(size);
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auto* header = (MallocHeader*)((((byte*)ptr) - sizeof(MallocHeader)));
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size_t old_size = header->size;
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if (size == old_size)
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return ptr;
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auto* new_ptr = malloc(size);
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memcpy(new_ptr, ptr, min(old_size, size));
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free(ptr);
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return new_ptr;
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}
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typedef void(*__atexit_handler)();
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static int __atexit_handler_count = 0;
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static __atexit_handler __atexit_handlers[32];
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