//参数值为使用到的slabclass数组元素个数
//为slabclass数组的每一个元素(使用到的元素)分配内存
static void slabs_preallocate (const unsigned int maxslabs) {
int i;
unsigned int prealloc = 0;
/* pre-allocate a 1MB slab in every size class so people don't get
confused by non-intuitive "SERVER_ERROR out of memory"
messages. this is the most common question on the mailing
list. if you really don't want this, you can rebuild without
these three lines. */
//遍历slabclass数组
for (i = POWER_SMALLEST; i <= POWER_LARGEST; i++) {
if (++prealloc > maxslabs)//当然是只遍历使用了的数组元素
return;
if (do_slabs_newslab(i) == 0) {//为每一个slabclass_t分配一个内存页
//如果分配失败，将退出程序.因为这个预分配的内存是后面程序运行的基础
//如果这里分配失败了，后面的代码无从执行。所以就直接退出程序
fprintf(stderr, "Error while preallocating slab memory!\n"
"If using -L or other prealloc options, max memory must be "
"at least %d megabytes.\n", power_largest);
exit(1);
}
}
}
void* Slab::do_slabs_alloc(size_t size, unsigned int id) {
void* ret = 0;
struct base_item *it = 0;
slabclass& p = mem_base[id];
if (id < POWER_SMALLEST || id > POWER_LARGEST) {
return (void*)0;
}
//查看是否freelist上没有东西了
if (! (p.sl_curr != 0 || do_slabs_newslab(id) != 0) ) {
return (void*)0;
}
else if (p.sl_curr != 0) {
//从freelist取出一个给他
it = (struct base_item*)(p.slots);
p.slots = it->next;
if (it->next)
it->next->prev = 0;
p.sl_curr--;
ret = (void*)it;
}
if (ret) {
p.requested += size;
}
return ret;
}
/*@null@*/
static void *do_slabs_alloc(const size_t size, unsigned int id) {
slabclass_t *p;
void *ret = NULL;
if (id < POWER_SMALLEST || id > power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &slabclass[id];
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
if (! (p->end_page_ptr != 0 || p->sl_curr != 0 ||
do_slabs_newslab(id) != 0)) {
/* We don't have more memory available */
ret = NULL;
} else if (p->sl_curr != 0) {
/* return off our freelist */
#ifdef TEST_LRU
item *it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
p->sl_curr--;
ret = (void *)it;
#endif
#ifdef TEST_CLOCK
/* return off our freelist */
slabbed_item* sl_it = (slabbed_item *)p->slots;
p->slots = sl_it->next;
if (sl_it->next) sl_it->next->prev = 0;
p->sl_curr--;
ret = (void *)sl_it;
#endif
} else {
/* if we recently allocated a whole page, return from that */
assert(p->end_page_ptr != NULL);
ret = p->end_page_ptr;
if (--p->end_page_free != 0) {
p->end_page_ptr = ((caddr_t)p->end_page_ptr) + p->size;
} else {
p->end_page_ptr = 0;
}
/* item *it = (item *)ret; */
/* reset_version(it); */
}
if (ret) {
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
/*@null@*/
static void *do_slabs_alloc(const size_t size, unsigned int id) {
slabclass_t *p;
void *ret = NULL;
item *it = NULL;
if (id < POWER_SMALLEST || id > power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &slabclass[id];
assert(p->sl_curr == 0 || ((item *)p->slots)->slabs_clsid == 0);
#ifdef USE_SYSTEM_MALLOC
if (mem_limit && mem_malloced + size > mem_limit) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
return 0;
}
mem_malloced += size;
ret = malloc(size);
MEMCACHED_SLABS_ALLOCATE(size, id, 0, ret);
return ret;
#endif
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
if (! (p->end_page_ptr != 0 || p->sl_curr != 0 ||
do_slabs_newslab(id) != 0)) {
/* We don't have more memory available */
ret = NULL;
} else if (p->sl_curr != 0) {
/* return off our freelist */
it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
p->sl_curr--;
ret = (void *)it;
} else {
/* if we recently allocated a whole page, return from that */
assert(p->end_page_ptr != NULL);
ret = p->end_page_ptr;
if (--p->end_page_free != 0) {
p->end_page_ptr = ((caddr_t)p->end_page_ptr) + p->size;
} else {
p->end_page_ptr = 0;
}
}
if (ret) {
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
/* This calculation ends up adding sizeof(void *) to the item size. */
static void *do_slabs_alloc_chunked(const size_t size, slabclass_t *p, unsigned int id) {
void *ret = NULL;
item *it = NULL;
int x;
int csize = p->size - sizeof(item_chunk);
unsigned int chunks_req = size / csize;
if (size % csize != 0)
chunks_req++;
while (p->sl_curr < chunks_req) {
if (do_slabs_newslab(id) == 0)
break;
}
if (p->sl_curr >= chunks_req) {
item_chunk *chunk = NULL;
/* Configure the head item in the chain. */
it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
/* Squirrel away the "top chunk" into h_next for now */
it->h_next = (item *)p->slots;
assert(it->h_next != 0);
chunk = (item_chunk *) it->h_next;
/* roll down the chunks, marking them as such. */
for (x = 0; x < chunks_req-1; x++) {
chunk->it_flags &= ~ITEM_SLABBED;
chunk->it_flags |= ITEM_CHUNK;
/* Chunks always have a direct reference to the head item */
chunk->head = it;
chunk->size = p->size - sizeof(item_chunk);
chunk->used = 0;
chunk = chunk->next;
}
/* The final "next" is now the top of the slab freelist */
p->slots = chunk;
if (chunk && chunk->prev) {
/* Disconnect the final chunk from the chain */
chunk->prev->next = 0;
chunk->prev = 0;
}
it->it_flags &= ~ITEM_SLABBED;
it->it_flags |= ITEM_CHUNKED;
it->refcount = 1;
p->sl_curr -= chunks_req;
ret = (void *)it;
} else {
ret = NULL;
}
return ret;
}
static void slabs_preallocate(const unsigned int maxslabs)
{
int i;
unsigned int prealloc = 0;
/* pre-allocate a 1MB slab in every size class so people don't get
confused by non-intuitive "SERVER_ERROR out of memory"
messages. this is the most common question on the mailing
list. if you really don't want this, you can rebuild without
these three lines. */
for (i = POWER_SMALLEST; i <= POWER_LARGEST; i++) {
if (++prealloc > maxslabs)
return;
do_slabs_newslab(i);
}
/* slab class 0 is used for collection items and small-size kv items */
do_slabs_newslab(0);
}
/*@null@*/
static void *do_slabs_alloc(const size_t size, unsigned int id) {
slabclass_t *p;
void *ret = NULL;
if (id < POWER_SMALLEST || id > power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
printf("%s:%d returning NULL from here\n", __func__, __LINE__);
return NULL;
}
p = &slabclass[id];
assert(p->sl_curr == 0 || ((item *)p->slots)->slabs_clsid == 0);
DBG_INFO(DBG_ASSOC_HOPSCOTCH, "%s:%d: sl_curr = %u\n", __func__, __LINE__, p->sl_curr);
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
if (! (p->sl_curr != 0 || do_slabs_newslab(id) != 0)) {
/* We don't have more memory available */
DBG_INFO(DBG_ASSOC_HOPSCOTCH, "%s:%d returning NULL from here\n", __func__, __LINE__);
ret = NULL;
} else if (p->sl_curr != 0) {
/* return off our freelist */
#ifdef HOPSCOTCH_CLOCK
slabbed_item* sl_it = (slabbed_item *)p->slots;
p->slots = sl_it->next;
if (sl_it->next) sl_it->next->prev = 0;
//DBG_INFO(DBG_ASSOC_HOPSCOTCH, "%s:%d: before it_flags = %u\n", __func__, __LINE__, sl_it->it_flags);
//__sync_fetch_and_and(&sl_it->it_flags, ~ITEM_SLABBED);
//DBG_INFO(DBG_ASSOC_HOPSCOTCH, "%s:%d: after it_flags = %u\n", __func__, __LINE__, sl_it->it_flags);
ret = (void *)sl_it;
#else
item *it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
/* Kill flag and initialize refcount here for lock safety in slab
* mover's freeness detection. */
DBG_INFO(DBG_ASSOC_HOPSCOTCH, "%s:%d: before it_flags = %u\n", __func__, __LINE__, sl_it->it_flags);
it->it_flags &= ~ITEM_SLABBED;
DBG_INFO(DBG_ASSOC_HOPSCOTCH, "%s:%d: after it_flags = %u\n", __func__, __LINE__, sl_it->it_flags);
it->refcount = 1;
ret = (void *)it;
#endif
p->sl_curr--;
}
if (ret) {
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
DBG_INFO(DBG_ASSOC_HOPSCOTCH, "%s:%d returning ret = %p from here\n", __func__, __LINE__, ret);
return ret;
}
void Slab::slabs_preallocate(const unsigned int maxslabs) {
int i;
unsigned int prealloc = 0;
for ( i = POWER_SMALLEST; i < power_largest; i++) {
if (++prealloc > maxslabs)
return;
if (do_slabs_newslab(i) == 0) {
std::cerr << "Error while preallocating slab class "<< i << " memory!\n";
exit(1);
}
}
}
/*@null@*/
static void *do_slabs_alloc(struct default_engine *engine, const size_t size, unsigned int id) {
slabclass_t *p;
void *ret = NULL;
if (id < POWER_SMALLEST || id > engine->slabs.power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &engine->slabs.slabclass[id];
#ifdef USE_SYSTEM_MALLOC
if (engine->slabs.mem_limit && engine->slabs.mem_malloced + size > engine->slabs.mem_limit) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
return 0;
}
engine->slabs.mem_malloced += size;
ret = malloc(size);
MEMCACHED_SLABS_ALLOCATE(size, id, 0, ret);
return ret;
#endif
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
if (! (p->end_page_ptr != 0 || p->sl_curr != 0 ||
do_slabs_newslab(engine, id) != 0)) {
/* We don't have more memory available */
ret = NULL;
} else if (p->sl_curr != 0) {
/* return off our freelist */
ret = p->slots[--p->sl_curr];
} else {
/* if we recently allocated a whole page, return from that */
cb_assert(p->end_page_ptr != NULL);
ret = p->end_page_ptr;
if (--p->end_page_free != 0) {
p->end_page_ptr = ((unsigned char *)p->end_page_ptr) + p->size;
} else {
p->end_page_ptr = 0;
}
}
if (ret) {
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
/*@null@*/
static void *do_slabs_alloc(const size_t size, unsigned int id, uint64_t *total_bytes,
unsigned int flags) {
slabclass_t *p;
void *ret = NULL;
item *it = NULL;
if (id < POWER_SMALLEST || id > power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &slabclass[id];
assert(p->sl_curr == 0 || ((item *)p->slots)->slabs_clsid == 0);
if (total_bytes != NULL) {
*total_bytes = p->requested;
}
if (size <= p->size) {
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
if (p->sl_curr == 0 && flags != SLABS_ALLOC_NO_NEWPAGE) {
do_slabs_newslab(id);
}
if (p->sl_curr != 0) {
/* return off our freelist */
it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
/* Kill flag and initialize refcount here for lock safety in slab
* mover's freeness detection. */
it->it_flags &= ~ITEM_SLABBED;
it->refcount = 1;
p->sl_curr--;
ret = (void *)it;
} else {
ret = NULL;
}
} else {
/* Dealing with a chunked item. */
ret = do_slabs_alloc_chunked(size, p, id);
}
if (ret) {
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
/*@null@*/
static void *do_slabs_alloc(slabs_t* pst, const size_t size, unsigned int id) {
slabclass_t *p;
void *ret = NULL;
slabheader_t *it = NULL;
if (id < POWER_SMALLEST || id > pst->power_largest) {
//MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &pst->slabclass[id];
//assert(p->sl_curr == 0 || ((slabheader_t*)p->slots)->slabs_clsid == 0);
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
if (! (p->end_page_ptr != 0 || p->sl_curr != 0 ||
do_slabs_newslab(pst, id) != 0)) {
/* We don't have more memory available */
ret = NULL;
} else if (p->sl_curr != 0) {
/* return off our freelist */
it = (slabheader_t*)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
p->sl_curr--;
ret = (void *)it;
} else {
/* if we recently allocated a whole page, return from that */
assert(p->end_page_ptr != NULL);
ret = p->end_page_ptr;
if (--p->end_page_free != 0) {
p->end_page_ptr = ((caddr_t)p->end_page_ptr) + p->size;
} else {
p->end_page_ptr = 0;
}
}
if (ret) {
p->requested += size;
//MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
//MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
//printf("alloc ps:%p sid:%u p:%p np:%p cnt:%u used:%lu rest:%u \n", pst, id, ret, p->end_page_ptr, p->sl_curr, p->requested, p->end_page_free);
return ret;
}
// 从slabclass中申请size大小的空间
static void *do_slabs_alloc(const size_t size, unsigned int id) {
slabclass_t *p;
void *ret = NULL;
item *it = NULL;
if (id < POWER_SMALLEST || id > power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &slabclass[id];
// 可以看出，有slab中的空间不仅只能通过slab_list获得，还可以通过slots来获得，
// 因为free出来的item是放在slots中的，即slots中的item其实是存储slab中的，由于
// 不好判断slab中的item是否被释放，所以搞出来一个slots来存储释放的item，这样就
// 不需要判断，而直接用即可。 这真是将指针的好处体现得淋漓尽致
assert(p->sl_curr == 0 || ((item *)p->slots)->slabs_clsid == 0);
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
// 这个新版本已经将所有用户内存分配都改为从slots中进行了，在newslab中的时候
// 已经将item信息全部存储slots中了。
// 当前sl_curr为0时，即没有了item，然后newslab，这样又有item放进去了，所以下面可以继续
// 分配
if (! (p->sl_curr != 0 || do_slabs_newslab(id) != 0)) {
/* We don't have more memory available */
ret = NULL;
} else if (p->sl_curr != 0) {
/* return off our freelist */
// 这里是从slots的头开始分配的
it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
p->sl_curr--;
ret = (void *)it;
}
if (ret) {
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
/*@null@*/
static void *do_slabs_alloc(const size_t size, unsigned int id) {
slabclass_t *p;
void *ret = NULL;
item *it = NULL;
if (id < POWER_SMALLEST || id > power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &slabclass[id];
assert(p->sl_curr == 0 || ((item *)p->slots)->slabs_clsid == 0);
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
/* 确保最后一个slab 有空闲的chunk */
if (! (p->sl_curr != 0 || do_slabs_newslab(id) != 0))
{
/* We don't have more memory available */
ret = NULL;
}
//从slabclass_t的空闲item链表中获取一个item
else if (p->sl_curr != 0)
{
/* return off our freelist */
it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
p->sl_curr--;
ret = (void *)it;
}
if (ret)
{
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
}
else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
// 从指定的 slabclass, 即 slabclass[id], 分配大小为 size 的内存块供申请者使用.
//
// 分配的原则是, 优先从 slots 指向的空闲链表中分配, 空闲链表没有, 才从 slab 中分配一个空闲的 chunk.
static void *do_slabs_alloc(const size_t size, unsigned int id, unsigned int *total_chunks) {
slabclass_t *p;
void *ret = NULL;
item *it = NULL;
if (id < POWER_SMALLEST || id > power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &slabclass[id];
assert(p->sl_curr == 0 || ((item *)p->slots)->slabs_clsid == 0);
*total_chunks = p->slabs * p->perslab;
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
// p->sl_curr == 0 && do_slabs_newslab(id) == 0
// TODO 若分配新的slab后，什么都不干？
if (! (p->sl_curr != 0 || do_slabs_newslab(id) != 0)) {
/* We don't have more memory available */
ret = NULL;
} else if (p->sl_curr != 0) {
/* return off our freelist */
it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
/* Kill flag and initialize refcount here for lock safety in slab
* mover's freeness detection. */
it->it_flags &= ~ITEM_SLABBED;
it->refcount = 1;
p->sl_curr--;
ret = (void *)it;
}
if (ret) {
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
//向slabclass申请一个item。在调用该函数之前，已经调用slabs_clsid函数确定
//本次申请是向哪个slabclass_t申请item了，参数id就是指明是向哪个slabclass_t
//申请item。如果该slabclass_t是有空闲item，那么就从空闲的item队列中分配一个
//如果没有空闲item，那么就申请一个内存页。再从新申请的页中分配一个item
//返回值为得到的item，如果没有内存了，返回NULL
static void *do_slabs_alloc(const size_t size, unsigned int id) {
slabclass_t *p;
void *ret = NULL;
item *it = NULL;
if (id < POWER_SMALLEST || id > power_largest) {//下标越界
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &slabclass[id];
assert(p->sl_curr == 0 || ((item *)p->slots)->slabs_clsid == 0);
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
//如果p->sl_curr等于0，就说明该slabclass_t没有空闲的item了
//此时需要调用do_slabs_newslab申请一个内存页
if (! (p->sl_curr != 0 || do_slabs_newslab(id) != 0)) {
/* We don't have more memory available */
//当p->sl_curr等于0并且do_slabs_newslab的返回值等于0时，进入这里
ret = NULL;
} else if (p->sl_curr != 0) {
//除非do_slabs_newslab调用失败，否则都会来到这里.无论一开始sl_curr是否为0。
//p->slots指向第一个空闲的item，此时要把第一个空闲的item分配出去
/* return off our freelist */
it = (item *)p->slots;
p->slots = it->next;//slots指向下一个空闲的item
if (it->next) it->next->prev = 0;
p->sl_curr--;//空闲数目减一
ret = (void *)it;
}
if (ret) {
p->requested += size;//增加本slabclass分配出去的字节数
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
//分配每个slab的内存空间,maxslabs表示已经初始化的slab的最大编号，即下标
static void slabs_preallocate (const unsigned int maxslabs)
{
int i;
unsigned int prealloc = 0;
/* pre-allocate a 1MB slab in every size class so people don't get confused by non-intuitive
"SERVER_ERROR out of memory" messages. this is the most common question on the mailing list.
if you really don't want this, you can rebuild without these three lines. */
for (i = POWER_SMALLEST; i <= POWER_LARGEST; i++)
{
if (++prealloc > maxslabs) return;
//执行分配操作，对第i个slabclass执行分配操作
if (do_slabs_newslab(i) == 0)
{
fprintf(stderr, "Error while preallocating slab memory!\n"
"If using -L or other prealloc options, max memory must be "
"at least %d megabytes.\n", power_largest);
exit(1);
}
}
}
/*@null@*/
void *do_slabs_alloc(const size_t size) {
slabclass_t *p;
unsigned int id = slabs_clsid(size);
if (id < POWER_SMALLEST || id > power_largest)
return NULL;
p = &slabclass[id];
assert(p->sl_curr == 0 || ((item *)p->slots[p->sl_curr - 1])->slabs_clsid == 0);
#ifdef USE_SYSTEM_MALLOC
if (mem_limit && mem_malloced + size > mem_limit)
return 0;
mem_malloced += size;
return malloc(size);
#endif
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
if (! (p->end_page_ptr != 0 || p->sl_curr != 0 || do_slabs_newslab(id) != 0))
return 0;
/* return off our freelist, if we have one */
if (p->sl_curr != 0)
return p->slots[--p->sl_curr];
/* if we recently allocated a whole page, return from that */
if (p->end_page_ptr) {
void *ptr = p->end_page_ptr;
if (--p->end_page_free != 0) {
p->end_page_ptr += p->size;
} else {
p->end_page_ptr = 0;
}
return ptr;
}
return NULL; /* shouldn't ever get here */
}