第0层
这是指使用glibc的malloc()方法去申请内存,当然这不是啥对象都用这个,而是取决于分配的内存大小
void *
PyObject_Malloc(size_t nbytes)
{
block *bp;
poolp pool;
poolp next;
uint size;
/*
* 异常处理
*/
if (nbytes > PY_SSIZE_T_MAX)
return NULL;
/*
* 需要分配的内存小于某个特定的值时
*/
if ((nbytes - 1) < SMALL_REQUEST_THRESHOLD) {
LOCK();
/*
* Most frequent paths first
*/
size = (uint)(nbytes - 1) >> ALIGNMENT_SHIFT;
pool = usedpools[size + size];
if (pool != pool->nextpool) {
/*
* There is a used pool for this size class.
* Pick up the head block of its free list.
*/
++pool->ref.count;
bp = pool->freeblock;
assert(bp != NULL);
if ((pool->freeblock = *(block **)bp) != NULL) {
UNLOCK();
return (void *)bp;
}
/*
* Reached the end of the free list, try to extend it.
*/
if (pool->nextoffset <= pool->maxnextoffset) {
/* There is room for another block. */
pool->freeblock = (block*)pool +
pool->nextoffset;
pool->nextoffset += INDEX2SIZE(size);
*(block **)(pool->freeblock) = NULL;
UNLOCK();
return (void *)bp;
}
/* Pool is full, unlink from used pools. */
next = pool->nextpool;
pool = pool->prevpool;
next->prevpool = pool;
pool->nextpool = next;
UNLOCK();
return (void *)bp;
}
/* There isn't a pool of the right size class immediately
* available: use a free pool.
*/
if (usable_arenas == NULL) {
/* No arena has a free pool: allocate a new arena. */
#ifdef WITH_MEMORY_LIMITS
if (narenas_currently_allocated >= MAX_ARENAS) {
UNLOCK();
goto redirect;
}
#endif
usable_arenas = new_arena();
if (usable_arenas == NULL) {
UNLOCK();
goto redirect;
}
usable_arenas->nextarena =
usable_arenas->prevarena = NULL;
}
assert(usable_arenas->address != 0);
/* Try to get a cached free pool. */
pool = usable_arenas->freepools;
if (pool != NULL) {
/* Unlink from cached pools. */
usable_arenas->freepools = pool->nextpool;
/* This arena already had the smallest nfreepools
* value, so decreasing nfreepools doesn't change
* that, and we don't need to rearrange the
* usable_arenas list. However, if the arena has
* become wholly allocated, we need to remove its
* arena_object from usable_arenas.
*/
--usable_arenas->nfreepools;
if (usable_arenas->nfreepools == 0) {
/* Wholly allocated: remove. */
assert(usable_arenas->freepools == NULL);
assert(usable_arenas->nextarena == NULL ||
usable_arenas->nextarena->prevarena ==
usable_arenas);
usable_arenas = usable_arenas->nextarena;
if (usable_arenas != NULL) {
usable_arenas->prevarena = NULL;
assert(usable_arenas->address != 0);
}
}
else {
/* nfreepools > 0: it must be that freepools
* isn't NULL, or that we haven't yet carved
* off all the arena's pools for the first
* time.
*/
assert(usable_arenas->freepools != NULL ||
usable_arenas->pool_address <=
(block*)usable_arenas->address +
ARENA_SIZE - POOL_SIZE);
}
init_pool:
/* Frontlink to used pools. */
next = usedpools[size + size]; /* == prev */
pool->nextpool = next;
pool->prevpool = next;
next->nextpool = pool;
next->prevpool = pool;
pool->ref.count = 1;
if (pool->szidx == size) {
/* Luckily, this pool last contained blocks
* of the same size class, so its header
* and free list are already initialized.
*/
bp = pool->freeblock;
pool->freeblock = *(block **)bp;
UNLOCK();
return (void *)bp;
}
/*
* Initialize the pool header, set up the free list to
* contain just the second block, and return the first
* block.
*/
pool->szidx = size;
size = INDEX2SIZE(size);
bp = (block *)pool + POOL_OVERHEAD;
pool->nextoffset = POOL_OVERHEAD + (size << 1);
pool->maxnextoffset = POOL_SIZE - size;
pool->freeblock = bp + size;
*(block **)(pool->freeblock) = NULL;
UNLOCK();
return (void *)bp;
}
/* Carve off a new pool. */
assert(usable_arenas->nfreepools > 0);
assert(usable_arenas->freepools == NULL);
pool = (poolp)usable_arenas->pool_address;
assert((block*)pool <= (block*)usable_arenas->address +
ARENA_SIZE - POOL_SIZE);
pool->arenaindex = usable_arenas - arenas;
assert(&arenas[pool->arenaindex] == usable_arenas);
pool->szidx = DUMMY_SIZE_IDX;
usable_arenas->pool_address += POOL_SIZE;
--usable_arenas->nfreepools;
if (usable_arenas->nfreepools == 0) {
assert(usable_arenas->nextarena == NULL ||
usable_arenas->nextarena->prevarena ==
usable_arenas);
/* Unlink the arena: it is completely allocated. */
usable_arenas = usable_arenas->nextarena;
if (usable_arenas != NULL) {
usable_arenas->prevarena = NULL;
assert(usable_arenas->address != 0);
}
}
goto init_pool;
}
/* The small block allocator ends here. */
redirect:
/* 异常处理
*/
if (nbytes == 0)
nbytes = 1;
/*
*大于的话直接分配,调用C的内置函数
*/
return (void *)malloc(nbytes);
}
备注:
在某些版本这个特定的值是256
#define SMALL_REQUEST_THRESHOLD 512
第一层的分配器
如果python的对象并不都是些大对象,并且其生成是循环,这时候就不能使用malloc了
而是先保留内存空间,再去分配
内存结构:
分为3个
block -> pool -> arena
首先来看arena
struct arena_object {
/* malloc之后的arena的地址
*/
uptr address;
/* 用于对齐pool的地址 */
block* pool_address;
/* 空闲的pool总数
*/
uint nfreepools;
/* pool的总数 */
uint ntotalpools;
/* 连接空闲pool的单向链表 */
struct pool_header* freepools;
/* Whenever this arena_object is not associated with an allocated
* arena, the nextarena member is used to link all unassociated
* arena_objects in the singly-linked `unused_arena_objects` list.
* The prevarena member is unused in this case.
*
* When this arena_object is associated with an allocated arena
* with at least one available pool, both members are used in the
* doubly-linked `usable_arenas` list, which is maintained in
* increasing order of `nfreepools` values.
*
* Else this arena_object is associated with an allocated arena
* all of whose pools are in use. `nextarena` and `prevarena`
* are both meaningless in this case.
*/
struct arena_object* nextarena;
struct arena_object* prevarena;
};
这个管理着arena,大小如下
#define ARENA_SIZE (256 << 10) /* 256KB */
arena还被arenas数组管理着
/* Array of objects used to track chunks of memory (arenas). */
static struct arena_object* arenas = NULL;
/* Number of slots currently allocated in the `arenas` vector. */
static uint maxarenas = 0;
此外的一些宏定义
#undef uchar
#define uchar unsigned char /* assuming == 8 bits */
#undef uint
#define uint unsigned int /* assuming >= 16 bits */
#undef ulong
#define ulong unsigned long /* assuming >= 32 bits */
/*这个用于将指针安全的转化为整数
*/
#undef uptr
#define uptr Py_uintptr_t
/* When you say memory, my mind reasons in terms of (pointers to) blocks */
typedef uchar block;
pool结构
取决于os的页面单位,4k
#define SYSTEM_PAGE_SIZE (4 * 1024)
#define POOL_SIZE SYSTEM_PAGE_SIZE /* must be 2^N */
arenade pool被划分为4k的大小,也就是说将pool的地址按照4k的倍数对齐,这也就意味着arena的地址不一定会和pool地址对齐
所以在struct里需要对齐
struct pool_header {
union { block *_padding;
uint count; } ref; /* 分配到pool里的block的数量 */
block *freeblock; /* block的空闲链表的开头 */
struct pool_header *nextpool; /* 指向下一个pool的指针(双向链表) */
struct pool_header *prevpool; /* 上一个的指针 "" */
uint arenaindex; /* 自己所属的arena的索引*/
uint szidx; /* 分配的block的大小 */
uint nextoffset; /* 到下一个block的位移 */
uint maxnextoffset; /* 最大有效偏移 */
};
这个将pool连接,保持pool内部block的大小和个数
下面是生成arena的代码
static struct arena_object*
new_arena(void)
{
struct arena_object* arenaobj;
uint excess; /* number of bytes above pool alignment */
void *address;
int err;
#ifdef PYMALLOC_DEBUG
if (Py_GETENV("PYTHONMALLOCSTATS"))
_PyObject_DebugMallocStats();
#endif
if (unused_arena_objects == NULL) {
uint i;
uint numarenas;
size_t nbytes;
/* maxarenas指的是arenas数组现有的元素数量,刚开始调用时,自然maxarenas为0
* Note that it's possible for `numarenas` to overflow.
*/
numarenas = maxarenas ? maxarenas << 1 : INITIAL_ARENA_OBJECTS;
if (numarenas <= maxarenas)
return NULL; /* overflow */
#if SIZEOF_SIZE_T <= SIZEOF_INT
if (numarenas > PY_SIZE_MAX / sizeof(*arenas))
return NULL; /* overflow */
#endif
nbytes = numarenas * sizeof(*arenas);
arenaobj = (struct arena_object *)realloc(arenas, nbytes);
if (arenaobj == NULL)
return NULL;
arenas = arenaobj;
/* We might need to fix pointers that were copied. However,
* new_arena only gets called when all the pages in the
* previous arenas are full. Thus, there are *no* pointers
* into the old array. Thus, we don't have to worry about
* invalid pointers. Just to be sure, some asserts:
*/
assert(usable_arenas == NULL);
assert(unused_arena_objects == NULL);
/* Put the new arenas on the unused_arena_objects list. */
for (i = maxarenas; i < numarenas; ++i) {
arenas[i].address = 0; /* mark as unassociated */
arenas[i].nextarena = i < numarenas - 1 ?
&arenas[i+1] : NULL;
}
/* Update globals. */
unused_arena_objects = &arenas[maxarenas];
maxarenas = numarenas;
}
/* Take the next available arena object off the head of the list. */
assert(unused_arena_objects != NULL);
arenaobj = unused_arena_objects;
unused_arena_objects = arenaobj->nextarena;
assert(arenaobj->address == 0);
#ifdef ARENAS_USE_MMAP
address = mmap(NULL, ARENA_SIZE, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
err = (address == MAP_FAILED);
#else
address = malloc(ARENA_SIZE);
err = (address == 0);
#endif
if (err) {
/* The allocation failed: return NULL after putting the
* arenaobj back.
*/
arenaobj->nextarena = unused_arena_objects;
unused_arena_objects = arenaobj;
return NULL;
}
arenaobj->address = (uptr)address;
++narenas_currently_allocated;
#ifdef PYMALLOC_DEBUG
++ntimes_arena_allocated;
if (narenas_currently_allocated > narenas_highwater)
narenas_highwater = narenas_currently_allocated;
#endif
arenaobj->freepools = NULL;
/* pool_address <- first pool-aligned address in the arena
nfreepools <- number of whole pools that fit after alignment */
arenaobj->pool_address = (block*)arenaobj->address;
arenaobj->nfreepools = ARENA_SIZE / POOL_SIZE;
assert(POOL_SIZE * arenaobj->nfreepools == ARENA_SIZE);
excess = (uint)(arenaobj->address & POOL_SIZE_MASK);
if (excess != 0) {
--arenaobj->nfreepools;
arenaobj->pool_address += POOL_SIZE - excess;
}
arenaobj->ntotalpools = arenaobj->nfreepools;
return arenaobj;
}
unused_arena_objects这个指的是
static struct arena_object* unused_arena_objects = NULL;
表示的是现在未使用的arena_object的单向链表(包含新生成和已废弃的)