void slabs_alloc_test(void) {
unsigned int total_chunk = 0;
const char *key = "charliezhao";
size_t nkey = strlen(key) + 1;
item *ptr = (item *)slabs_alloc(1024, slabs_clsid(1024), &total_chunk);
strcpy(ITEM_key(ptr), key);
ptr->nkey = nkey;
strcpy(ITEM_data(ptr), "xuechaozhao");
uint32_t hv = jenkins_hash(key, strlen(key));
assoc_insert(ptr, hv);
for(int i = 0; i <= 10922; ++i) {
void *ptr = slabs_alloc(96, slabs_clsid(96), &total_chunk);
if(ptr == NULL) {
fprintf(stderr, "i: %7d slabs_alloc fail\n",
i);
break;
}
else {
slabs_free(ptr, 96, slabs_clsid(96));
}
}
item *ptr2 = assoc_find(key, nkey, hv);
fprintf(stdout, "key:%20s value:%20s\n", ITEM_key(ptr2), ITEM_data(ptr2));
}
item *item_alloc(char *key, int flags, rel_time_t exptime, int nbytes) {
int nsuffix, ntotal, len;
item *it;
unsigned int id;
char suffix[40];
ntotal = item_make_header(key, flags, nbytes, suffix, &nsuffix, &len);
id = slabs_clsid(ntotal);
if (id == 0)
return 0;
it = slabs_alloc(ntotal);
if (it == 0) {
int tries = 50;
item *search;
/* If requested to not push old items out of cache when memory runs out,
* we're out of luck at this point...
*/
if (!settings.evict_to_free) return 0;
/*
* try to get one off the right LRU
* don't necessariuly unlink the tail because it may be locked: refcount>0
* search up from tail an item with refcount==0 and unlink it; give up after 50
* tries
*/
if (id > LARGEST_ID) return 0;
if (tails[id]==0) return 0;
for (search = tails[id]; tries>0 && search; tries--, search=search->prev) {
if (search->refcount==0) {
item_unlink(search);
break;
}
}
it = slabs_alloc(ntotal);
if (it==0) return 0;
}
assert(it->slabs_clsid == 0);
it->slabs_clsid = id;
assert(it != heads[it->slabs_clsid]);
it->next = it->prev = it->h_next = 0;
it->refcount = 0;
it->it_flags = 0;
it->nkey = len;
it->nbytes = nbytes;
strcpy(ITEM_key(it), key);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, nsuffix);
it->nsuffix = nsuffix;
return it;
}
void *slabs_alloc(slabs_t* pst, size_t size) {
void *ret;
size += sizeof(slabheader_t);
unsigned int id = slabs_clsid(pst, size);
ret = do_slabs_alloc(pst, size, id);
return (void*)((char*)ret + sizeof(slabheader_t));
}
void slabs_free(void *ptr, unsigned int size) {
unsigned char id = slabs_clsid(size);
slabclass_t *p;
assert(((item *)ptr)->slabs_clsid==0);
assert(id >= POWER_SMALLEST && id <= POWER_LARGEST);
if (id < POWER_SMALLEST || id > POWER_LARGEST)
return;
p = &slabclass[id];
#ifdef USE_SYSTEM_MALLOC
mem_malloced -= size;
free(ptr);
return;
#endif
if (p->sl_curr == p->sl_total) { /* need more space on the free list */
int new_size = p->sl_total ? p->sl_total*2 : 16; /* 16 is arbitrary */
void **new_slots = realloc(p->slots, new_size*sizeof(void *));
if (new_slots == 0)
return;
p->slots = new_slots;
p->sl_total = new_size;
}
p->slots[p->sl_curr++] = ptr;
return;
}
/*
* Returns true if an item will fit in the cache (its size does not exceed
* the maximum for a cache entry.)
*/
int item_size_ok(char *key, int flags, int nbytes) {
char prefix[40];
int keylen, nsuffix;
return slabs_clsid(item_make_header(key, flags, nbytes,
prefix, &nsuffix, &keylen)) != 0;
}
/**
* Returns true if an item will fit in the cache (its size does not exceed
* the maximum for a cache entry.)
*/
bool item_size_ok(const size_t nkey, const int flags, const int nbytes) {
char prefix[40];
uint8_t nsuffix;
return slabs_clsid(item_make_header(nkey + 1, flags, nbytes,
prefix, &nsuffix)) != 0;
}
void slabs_free(slabs_t* pst, void *ptr, size_t size) {
void *header;
size += sizeof(slabheader_t);
unsigned int id = slabs_clsid(pst, size);
header = (void*)((char*)ptr - sizeof(slabheader_t));
do_slabs_free(pst, header, size, id);
}
unsigned int slabs_space_size(struct default_engine *engine, const size_t size)
{
if (size <= MAX_SM_VALUE_SIZE) {
return SMMGR_SLOT_SIZE(size);
}
int clsid = slabs_clsid(engine, size);
if (clsid == 0)
return 0;
else
return engine->slabs.slabclass[clsid].size;
}
/**
* Returns true if an item will fit in the cache (its size does not exceed
* the maximum for a cache entry.)
*/
bool item_size_ok(const size_t nkey, const int flags, const int nbytes) {
char prefix[40];
uint8_t nsuffix;
size_t ntotal = item_make_header(nkey + 1, flags, nbytes,
prefix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
return slabs_clsid(ntotal) != 0;
}
//检验item是否有合适的slab来存储
bool item_size_ok(const size_t nkey, const int flags, const int nbytes) {
syslog(LOG_INFO, "[%s:%s:%d]", __FILE__, __func__, __LINE__);
char prefix[40];
uint8_t nsuffix;
size_t ntotal = item_make_header(nkey + 1, flags, nbytes,
prefix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
return slabs_clsid(ntotal) != 0;
}
void *slabs_alloc(unsigned int size) {
slabclass_t *p;
unsigned char id = slabs_clsid(size);
if (id < POWER_SMALLEST || id > POWER_LARGEST)
return 0;
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 || p->sl_curr || slabs_newslab(id)))
return 0;
/* return off our freelist, if we have one */
if (p->sl_curr)
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) {
p->end_page_ptr += p->size;
} else {
p->end_page_ptr = 0;
}
return ptr;
}
return 0; /* shouldn't ever get here */
}
/*@null@*/
item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_time_t exptime, const int nbytes) {
uint8_t nsuffix;
item *it = NULL;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
/* do a quick check if we have any expired items in the tail.. */
int tries = 50;
item *search;
for (search = tails[id];
tries > 0 && search != NULL;
tries--, search=search->prev) {
if (search->refcount == 0 &&
(search->exptime != 0 && search->exptime < current_time)) {
it = search;
/* I don't want to actually free the object, just steal
* the item to avoid to grab the slab mutex twice ;-)
*/
it->refcount = 1;
do_item_unlink(it);
/* Initialize the item block: */
it->slabs_clsid = 0;
it->refcount = 0;
break;
}
}
if (it == NULL && (it = slabs_alloc(ntotal, id)) == NULL) {
/*
** Could not find an expired item at the tail, and memory allocation
** failed. Try to evict some items!
*/
tries = 50;
/* If requested to not push old items out of cache when memory runs out,
* we're out of luck at this point...
*/
if (settings.evict_to_free == 0) {
itemstats[id].outofmemory++;
return NULL;
}
/*
* try to get one off the right LRU
* don't necessariuly unlink the tail because it may be locked: refcount>0
* search up from tail an item with refcount==0 and unlink it; give up after 50
* tries
*/
if (tails[id] == 0) {
itemstats[id].outofmemory++;
return NULL;
}
for (search = tails[id]; tries > 0 && search != NULL; tries--, search=search->prev) {
if (search->refcount == 0) {
if (search->exptime == 0 || search->exptime > current_time) {
itemstats[id].evicted++;
itemstats[id].evicted_time = current_time - search->time;
STATS_LOCK();
stats.evictions++;
STATS_UNLOCK();
}
do_item_unlink(search);
break;
}
}
it = slabs_alloc(ntotal, id);
if (it == 0) {
itemstats[id].outofmemory++;
/* Last ditch effort. There is a very rare bug which causes
* refcount leaks. We've fixed most of them, but it still happens,
* and it may happen in the future.
* We can reasonably assume no item can stay locked for more than
* three hours, so if we find one in the tail which is that old,
* free it anyway.
*/
tries = 50;
for (search = tails[id]; tries > 0 && search != NULL; tries--, search=search->prev) {
if (search->refcount != 0 && search->time + TAIL_REPAIR_TIME < current_time) {
itemstats[id].tailrepairs++;
search->refcount = 0;
do_item_unlink(search);
break;
}
}
it = slabs_alloc(ntotal, id);
if (it == 0) {
return NULL;
}
}
}
assert(it->slabs_clsid == 0);
it->slabs_clsid = id;
assert(it != heads[it->slabs_clsid]);
it->next = it->prev = it->h_next = 0;
it->refcount = 1; /* the caller will have a reference */
DEBUG_REFCNT(it, '*');
it->it_flags = settings.use_cas ? ITEM_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
memcpy(ITEM_key(it), key, nkey);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}
/*@null@*/
item *do_item_alloc(char *key, const size_t nkey, const int flags,
const rel_time_t exptime, const int nbytes,
const uint32_t cur_hv) {
uint8_t nsuffix;
ck_spinlock_mcs_context_t second_lock;
item *it = NULL;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
LOCK_CLOCK();
/* Avoid hangs if a slab has nothing but refcounted stuff in it. */
/* int tries_lrutail_reflocked = 1000; */
item *search;
item *next_it;
void *hold_lock = NULL;
/* We have no expiration. Try alloc a new one first. */
if ((it = slabs_alloc(ntotal, id)) == NULL) {
printf("item slab alloc fails\n");
assert(0);
/* doing CLOCK eviction */
search = hand[id];
if (!search) {
/* no mem from alloc or replace */
UNLOCK_CLOCK();
return NULL;
}
/* scan loop of the clock, which could be potentially
* unbounded -- we may want an upper limit for it. */
for (search = hand[id]; search != NULL; search = next_it) {
assert(search);
/* we might relink search mid-loop, so search->prev isn't reliable */
next_it = search->prev;
// if (*key == 101) printf("aaa %d\n", sizes[id]);
if (search->nbytes == 0 && search->nkey == 0 && search->it_flags == 1) {
/* We are a crawler, ignore it. */
continue;
}
uint32_t hv = hash(ITEM_key(search), search->nkey);
/* Attempt to hash item lock the "search" item. If locked, no
* other callers can incr the refcount
*/
/* Don't accidentally grab ourselves, or bail if we can't quicklock */
if (hv == cur_hv || (hold_lock = item_try_mcslock(hv, &second_lock)) == NULL)
continue;
/* Now see if the item is refcount locked */
if (refcount_incr(&search->refcount) != 2) {
/* Avoid pathological case with ref'ed items in tail */
do_item_update_nolock(search);
/* tries_lrutail_reflocked--; */
refcount_decr(&search->refcount);
itemstats[id].lrutail_reflocked++;
/* Old rare bug could cause a refcount leak. We haven't seen
* it in years, but we leave this code in to prevent failures
* just in case */
if (settings.tail_repair_time &&
search->time + settings.tail_repair_time < current_time) {
itemstats[id].tailrepairs++;
search->refcount = 1;
do_item_unlink_nolock(search, hv);
}
if (hold_lock)
item_try_mcsunlock(hold_lock, &second_lock);
/* if (tries_lrutail_reflocked < 1) */
/* break; */
continue;
}
if (search->recency) {
/* recently accessed. clear bit and continue. */
search->recency = 0;
continue;
}
// printf("aaa %d, %d\n", sizes[id], *key);
itemstats[id].evicted++;
itemstats[id].evicted_time = current_time - search->time;
if (search->exptime != 0)
itemstats[id].evicted_nonzero++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
itemstats[id].evicted_unfetched++;
}
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
do_item_unlink_nolock(it, hv);
/* Initialize the item block: */
it->slabs_clsid = 0;
refcount_decr(&search->refcount);
/* If hash values were equal, we don't grab a second lock */
if (hold_lock)
item_try_mcsunlock(hold_lock, &second_lock);
break;
}
/* end of loop*/
}
/* end of allocation / eviction */
if (it == NULL) {
itemstats[id].outofmemory++;
UNLOCK_CLOCK();
return NULL;
}
assert(it->slabs_clsid == 0);
/* Item initialization can happen outside of the lock; the item's already
* been removed from the slab LRU.
*/
it->refcount = 1; /* the caller will have a reference */
UNLOCK_CLOCK();
it->next = it->prev = it->h_next = 0;
it->slabs_clsid = id;
DEBUG_REFCNT(it, '*');
it->it_flags = settings.use_cas ? ITEM_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
memcpy(ITEM_key(it), key, nkey);
it->exptime = 0; //exptime; /* disable expiration. */
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}
item *do_item_alloc(char *key, const size_t nkey, const unsigned int flags,
const rel_time_t exptime, const int nbytes) {
int i;
uint8_t nsuffix;
item *it = NULL;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
/* If no memory is available, attempt a direct LRU juggle/eviction */
/* This is a race in order to simplify lru_pull_tail; in cases where
* locked items are on the tail, you want them to fall out and cause
* occasional OOM's, rather than internally work around them.
* This also gives one fewer code path for slab alloc/free
*/
/* TODO: if power_largest, try a lot more times? or a number of times
* based on how many chunks the new object should take up?
* or based on the size of an object lru_pull_tail() says it evicted?
* This is a classical GC problem if "large items" are of too varying of
* sizes. This is actually okay here since the larger the data, the more
* bandwidth it takes, the more time we can loop in comparison to serving
* and replacing small items.
*/
for (i = 0; i < 10; i++) {
uint64_t total_bytes;
/* Try to reclaim memory first */
if (!settings.lru_maintainer_thread) {
lru_pull_tail(id, COLD_LRU, 0, 0);
}
it = slabs_alloc(ntotal, id, &total_bytes, 0);
if (settings.expirezero_does_not_evict)
total_bytes -= noexp_lru_size(id);
if (it == NULL) {
if (settings.lru_maintainer_thread) {
lru_pull_tail(id, HOT_LRU, total_bytes, 0);
lru_pull_tail(id, WARM_LRU, total_bytes, 0);
if (lru_pull_tail(id, COLD_LRU, total_bytes, LRU_PULL_EVICT) <= 0)
break;
} else {
if (lru_pull_tail(id, COLD_LRU, 0, LRU_PULL_EVICT) <= 0)
break;
}
} else {
break;
}
}
if (i > 0) {
pthread_mutex_lock(&lru_locks[id]);
itemstats[id].direct_reclaims += i;
pthread_mutex_unlock(&lru_locks[id]);
}
if (it == NULL) {
pthread_mutex_lock(&lru_locks[id]);
itemstats[id].outofmemory++;
pthread_mutex_unlock(&lru_locks[id]);
return NULL;
}
assert(it->slabs_clsid == 0);
//assert(it != heads[id]);
/* Refcount is seeded to 1 by slabs_alloc() */
it->next = it->prev = 0;
/* Items are initially loaded into the HOT_LRU. This is '0' but I want at
* least a note here. Compiler (hopefully?) optimizes this out.
*/
if (settings.lru_maintainer_thread) {
if (exptime == 0 && settings.expirezero_does_not_evict) {
id |= NOEXP_LRU;
} else {
id |= HOT_LRU;
}
} else {
/* There is only COLD in compat-mode */
id |= COLD_LRU;
}
it->slabs_clsid = id;
DEBUG_REFCNT(it, '*');
it->it_flags |= settings.use_cas ? ITEM_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
memcpy(ITEM_key(it), key, nkey);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
/* Need to shuffle the pointer stored in h_next into it->data. */
if (it->it_flags & ITEM_CHUNKED) {
item_chunk *chunk = (item_chunk *) ITEM_data(it);
chunk->next = (item_chunk *) it->h_next;
chunk->prev = 0;
chunk->head = it;
/* Need to chain back into the head's chunk */
chunk->next->prev = chunk;
chunk->size = chunk->next->size - ((char *)chunk - (char *)it);
chunk->used = 0;
assert(chunk->size > 0);
}
it->h_next = 0;
return it;
}
//分配一个item，这个函数包含了memcached具体item分配的逻辑
item *do_item_alloc(char *key, const size_t nkey, const int flags,
const rel_time_t exptime, const int nbytes,
const uint32_t cur_hv) {
uint8_t nsuffix;
item *it = NULL;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix); //item总大小
if (settings.use_cas) {
ntotal += sizeof(uint64_t); //如果有用到cas，那么item大小还要加上unit64_t的size
}
unsigned int id = slabs_clsid(ntotal); //根据item的大小，找到适合的slabclass
if (id == 0)
return 0;
mutex_lock(&cache_lock); //cache锁
/* do a quick check if we have any expired items in the tail.. */
int tries = 5;
int tried_alloc = 0;
item *search;
void *hold_lock = NULL;
rel_time_t oldest_live = settings.oldest_live;
search = tails[id]; //全局变量，tails[x]是id为x的slabclass lru链表的尾部
/* We walk up *only* for locked items. Never searching for expired.
* Waste of CPU for almost all deployments */
//首先从lru链表尾部查找有没有过期的item，tries = 5，最多循环5次
//注意这里是最多查找5次，只要找到一个没有被其他地方引用的item，那么就不再继续查找，如果这个item过期，就使用这个item的空间，否则创建新的slab
for (; tries > 0 && search != NULL; tries--, search=search->prev) {
if (search->nbytes == 0 && search->nkey == 0 && search->it_flags == 1) {
/* We are a crawler, ignore it. */
//这里只是搜索过期的item，对于异常的item，直接忽略继续查找
tries++;
continue;
}
//计算item的hash值，hv有两个作用：1.用于hash表保存item 2.用于item lock表中锁住item，通过hv计算出item_lock中哪个锁对当前item加锁
//不同item的hash值可能相同，hash表中用链表的方式解决冲突；item lock中多个item共享一个锁
uint32_t hv = hash(ITEM_key(search), search->nkey);
/* Attempt to hash item lock the "search" item. If locked, no
* other callers can incr the refcount
*/
/* Don't accidentally grab ourselves, or bail if we can't quicklock */
//锁住当前item
if (hv == cur_hv || (hold_lock = item_trylock(hv)) == NULL)
continue;
/* Now see if the item is refcount locked */
//检查这个指向的这个item是否被其他地方引用，如果是的话，继续向前查找
if (refcount_incr(&search->refcount) != 2) {
refcount_decr(&search->refcount);
/* Old rare bug could cause a refcount leak. We haven't seen
* it in years, but we leave this code in to prevent failures
* just in case */
if (settings.tail_repair_time &&
search->time + settings.tail_repair_time < current_time) {
itemstats[id].tailrepairs++;
search->refcount = 1;
do_item_unlink_nolock(search, hv);
}
if (hold_lock)
item_trylock_unlock(hold_lock);
continue;
}
/* Expired or flushed */
//如果找到过期的item
if ((search->exptime != 0 && search->exptime < current_time)
|| (search->time <= oldest_live && oldest_live <= current_time)) {
itemstats[id].reclaimed++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
itemstats[id].expired_unfetched++;
}
it = search;
//更新统计数据
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
//把旧的item从hash表和LRU链表中移除
do_item_unlink_nolock(it, hv);
/* Initialize the item block: */
it->slabs_clsid = 0;
}
//如果没有找到过期的item，则调用slabs_alloc分配空间
//如果slabs_alloc返回null，表示分配失败，内存空间已满
//需要按LRU进行淘汰
else if ((it = slabs_alloc(ntotal, id)) == NULL) {
tried_alloc = 1; //标记一下，表示有尝试调用slabs_alloc分配空间
//记录被淘汰item的信息, 使用memcached经常会查看的evicted_time就是在这里赋值的
if (settings.evict_to_free == 0) {
itemstats[id].outofmemory++;
} else {
itemstats[id].evicted++;
itemstats[id].evicted_time = current_time - search->time; //被淘汰item距离上次使用的时间
if (search->exptime != 0)
itemstats[id].evicted_nonzero++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
itemstats[id].evicted_unfetched++;
}
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal); //更新统计数据
do_item_unlink_nolock(it, hv); //从hash表和LRU链表中移除
/* Initialize the item block: */
it->slabs_clsid = 0;
/* If we've just evicted an item, and the automover is set to
* angry bird mode, attempt to rip memory into this slab class.
* TODO: Move valid object detection into a function, and on a
* "successful" memory pull, look behind and see if the next alloc
* would be an eviction. Then kick off the slab mover before the
* eviction happens.
*/
//默认情况下，slab_automove=1，会合理地更具淘汰统计数据来分析怎么进行slabclass空间的分配
//如果slab_automove=2，只要分配失败了，马上进行slabclass空间的重分配
if (settings.slab_automove == 2)
slabs_reassign(-1, id);
}
}
refcount_decr(&search->refcount);
/* If hash values were equal, we don't grab a second lock */
if (hold_lock)
item_trylock_unlock(hold_lock);
break;
}
//查找5次过期的item都失败，并且也没有淘汰可用且没有过期的item
//分配新的内存空间
if (!tried_alloc && (tries == 0 || search == NULL))
it = slabs_alloc(ntotal, id);
//分配失败，返回null
if (it == NULL) {
itemstats[id].outofmemory++;
mutex_unlock(&cache_lock);
return NULL;
}
assert(it->slabs_clsid == 0);
assert(it != heads[id]);
/* Item initialization can happen outside of the lock; the item's already
* been removed from the slab LRU.
*/
//item内存空间分配成功，做一些初始化工作
it->refcount = 1; /* the caller will have a reference */
mutex_unlock(&cache_lock);
it->next = it->prev = it->h_next = 0;
it->slabs_clsid = id;
DEBUG_REFCNT(it, '*');
it->it_flags = settings.use_cas ? ITEM_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
memcpy(ITEM_key(it), key, nkey);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}
/*@null@*/
hash_item *do_item_alloc(struct default_engine *engine,
const void *key,
const size_t nkey,
const int flags,
const rel_time_t exptime,
const int nbytes,
const void *cookie) {
hash_item *it = NULL;
size_t ntotal = sizeof(hash_item) + nkey + nbytes;
if (engine->config.use_cas) {
ntotal += sizeof(uint64_t);
}
unsigned int id = slabs_clsid(engine, ntotal);
if (id == 0)
return 0;
/* do a quick check if we have any expired items in the tail.. */
int tries = search_items;
hash_item *search;
rel_time_t current_time = engine->server.core->get_current_time();
for (search = engine->items.tails[id];
tries > 0 && search != NULL;
tries--, search=search->prev) {
if (search->refcount == 0 &&
(search->exptime != 0 && search->exptime < current_time)) {
it = search;
/* I don't want to actually free the object, just steal
* the item to avoid to grab the slab mutex twice ;-)
*/
pthread_mutex_lock(&engine->stats.lock);
engine->stats.reclaimed++;
pthread_mutex_unlock(&engine->stats.lock);
engine->items.itemstats[id].reclaimed++;
it->refcount = 1;
slabs_adjust_mem_requested(engine, it->slabs_clsid, ITEM_ntotal(engine, it), ntotal);
do_item_unlink(engine, it);
/* Initialize the item block: */
it->slabs_clsid = 0;
it->refcount = 0;
break;
}
}
if (it == NULL && (it = slabs_alloc(engine, ntotal, id)) == NULL) {
/*
** Could not find an expired item at the tail, and memory allocation
** failed. Try to evict some items!
*/
tries = search_items;
/* If requested to not push old items out of cache when memory runs out,
* we're out of luck at this point...
*/
if (engine->config.evict_to_free == 0) {
engine->items.itemstats[id].outofmemory++;
return NULL;
}
/*
* try to get one off the right LRU
* don't necessariuly unlink the tail because it may be locked: refcount>0
* search up from tail an item with refcount==0 and unlink it; give up after search_items
* tries
*/
if (engine->items.tails[id] == 0) {
engine->items.itemstats[id].outofmemory++;
return NULL;
}
for (search = engine->items.tails[id]; tries > 0 && search != NULL; tries--, search=search->prev) {
if (search->refcount == 0) {
if (search->exptime == 0 || search->exptime > current_time) {
engine->items.itemstats[id].evicted++;
engine->items.itemstats[id].evicted_time = current_time - search->time;
if (search->exptime != 0) {
engine->items.itemstats[id].evicted_nonzero++;
}
pthread_mutex_lock(&engine->stats.lock);
engine->stats.evictions++;
pthread_mutex_unlock(&engine->stats.lock);
engine->server.stat->evicting(cookie,
item_get_key(search),
search->nkey);
} else {
engine->items.itemstats[id].reclaimed++;
pthread_mutex_lock(&engine->stats.lock);
engine->stats.reclaimed++;
pthread_mutex_unlock(&engine->stats.lock);
}
do_item_unlink(engine, search);
break;
}
}
it = slabs_alloc(engine, ntotal, id);
if (it == 0) {
engine->items.itemstats[id].outofmemory++;
/* Last ditch effort. There is a very rare bug which causes
* refcount leaks. We've fixed most of them, but it still happens,
* and it may happen in the future.
* We can reasonably assume no item can stay locked for more than
* three hours, so if we find one in the tail which is that old,
* free it anyway.
*/
tries = search_items;
for (search = engine->items.tails[id]; tries > 0 && search != NULL; tries--, search=search->prev) {
if (search->refcount != 0 && search->time + TAIL_REPAIR_TIME < current_time) {
engine->items.itemstats[id].tailrepairs++;
search->refcount = 0;
do_item_unlink(engine, search);
break;
}
}
it = slabs_alloc(engine, ntotal, id);
if (it == 0) {
return NULL;
}
}
}
assert(it->slabs_clsid == 0);
it->slabs_clsid = id;
assert(it != engine->items.heads[it->slabs_clsid]);
it->next = it->prev = it->h_next = 0;
it->refcount = 1; /* the caller will have a reference */
DEBUG_REFCNT(it, '*');
it->iflag = engine->config.use_cas ? ITEM_WITH_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
it->flags = flags;
memcpy((void*)item_get_key(it), key, nkey);
it->exptime = exptime;
return it;
}
/*@null@*/
item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_time_t exptime, const int nbytes) {
uint8_t nsuffix;
item *it = NULL;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
mutex_lock(&cache_lock);
/* do a quick check if we have any expired items in the tail.. */
item *search;
rel_time_t oldest_live = settings.oldest_live;
search = tails[id];
if (search != NULL && (refcount_incr(&search->refcount) == 2)) {
if ((search->exptime != 0 && search->exptime < current_time)
|| (search->time <= oldest_live && oldest_live <= current_time)) { // dead by flush
STATS_LOCK();
stats.reclaimed++;
STATS_UNLOCK();
itemstats[id].reclaimed++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
STATS_LOCK();
stats.expired_unfetched++;
STATS_UNLOCK();
itemstats[id].expired_unfetched++;
}
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
do_item_unlink_nolock(it, hash(ITEM_key(it), it->nkey, 0));
/* Initialize the item block: */
it->slabs_clsid = 0;
} else if ((it = slabs_alloc(ntotal, id)) == NULL) {
if (settings.evict_to_free == 0) {
itemstats[id].outofmemory++;
mutex_unlock(&cache_lock);
return NULL;
}
itemstats[id].evicted++;
itemstats[id].evicted_time = current_time - search->time;
if (search->exptime != 0)
itemstats[id].evicted_nonzero++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
STATS_LOCK();
stats.evicted_unfetched++;
STATS_UNLOCK();
itemstats[id].evicted_unfetched++;
}
STATS_LOCK();
stats.evictions++;
STATS_UNLOCK();
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
do_item_unlink_nolock(it, hash(ITEM_key(it), it->nkey, 0));
/* Initialize the item block: */
it->slabs_clsid = 0;
/* If we've just evicted an item, and the automover is set to
* angry bird mode, attempt to rip memory into this slab class.
* TODO: Move valid object detection into a function, and on a
* "successful" memory pull, look behind and see if the next alloc
* would be an eviction. Then kick off the slab mover before the
* eviction happens.
*/
if (settings.slab_automove == 2)
slabs_reassign(-1, id, 1);
} else {
refcount_decr(&search->refcount);
}
} else {
/* If the LRU is empty or locked, attempt to allocate memory */
it = slabs_alloc(ntotal, id);
if (search != NULL)
refcount_decr(&search->refcount);
}
if (it == NULL) {
itemstats[id].outofmemory++;
/* Last ditch effort. There was a very rare bug which caused
* refcount leaks. We leave this just in case they ever happen again.
* We can reasonably assume no item can stay locked for more than
* three hours, so if we find one in the tail which is that old,
* free it anyway.
*/
if (search != NULL &&
search->refcount != 2 &&
search->time + TAIL_REPAIR_TIME < current_time) {
itemstats[id].tailrepairs++;
search->refcount = 1;
do_item_unlink_nolock(search, hash(ITEM_key(search), search->nkey, 0));
}
mutex_unlock(&cache_lock);
return NULL;
}
assert(it->slabs_clsid == 0);
assert(it != heads[id]);
/* Item initialization can happen outside of the lock; the item's already
* been removed from the slab LRU.
*/
it->refcount = 1; /* the caller will have a reference */
mutex_unlock(&cache_lock);
it->next = it->prev = it->h_next = 0;
it->slabs_clsid = id;
DEBUG_REFCNT(it, '*');
it->it_flags = settings.use_cas ? ITEM_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
memcpy(ITEM_key(it), key, nkey);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}
static void *storage_write_thread(void *arg) {
void *storage = arg;
// NOTE: ignoring overflow since that would take years of uptime in a
// specific load pattern of never going to sleep.
unsigned int backoff[MAX_NUMBER_OF_SLAB_CLASSES] = {0};
unsigned int counter = 0;
useconds_t to_sleep = WRITE_SLEEP_MIN;
logger *l = logger_create();
if (l == NULL) {
fprintf(stderr, "Failed to allocate logger for storage compaction thread\n");
abort();
}
pthread_mutex_lock(&storage_write_plock);
while (1) {
// cache per-loop to avoid calls to the slabs_clsid() search loop
int min_class = slabs_clsid(settings.ext_item_size);
bool do_sleep = true;
counter++;
if (to_sleep > WRITE_SLEEP_MAX)
to_sleep = WRITE_SLEEP_MAX;
for (int x = 0; x < MAX_NUMBER_OF_SLAB_CLASSES; x++) {
bool did_move = false;
bool mem_limit_reached = false;
unsigned int chunks_free;
int item_age;
int target = settings.ext_free_memchunks[x];
if (min_class > x || (backoff[x] && (counter % backoff[x] != 0))) {
// Long sleeps means we should retry classes sooner.
if (to_sleep > WRITE_SLEEP_MIN * 10)
backoff[x] /= 2;
continue;
}
// Avoid extra slab lock calls during heavy writing.
chunks_free = slabs_available_chunks(x, &mem_limit_reached,
NULL, NULL);
// storage_write() will fail and cut loop after filling write buffer.
while (1) {
// if we are low on chunks and no spare, push out early.
if (chunks_free < target && mem_limit_reached) {
item_age = 0;
} else {
item_age = settings.ext_item_age;
}
if (storage_write(storage, x, item_age)) {
chunks_free++; // Allow stopping if we've done enough this loop
did_move = true;
do_sleep = false;
if (to_sleep > WRITE_SLEEP_MIN)
to_sleep /= 2;
} else {
break;
}
}
if (!did_move) {
backoff[x]++;
} else if (backoff[x]) {
backoff[x] /= 2;
}
}
// flip lock so we can be paused or stopped
pthread_mutex_unlock(&storage_write_plock);
if (do_sleep) {
usleep(to_sleep);
to_sleep *= 2;
}
pthread_mutex_lock(&storage_write_plock);
}
return NULL;
}
/*@null@*/
item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_time_t exptime, const int nbytes) {
uint8_t nsuffix;
item *it;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
it = slabs_alloc(ntotal, id);
if (it == 0) {
int tries = 50;
item *search;
/* If requested to not push old items out of cache when memory runs out,
* we're out of luck at this point...
*/
if (settings.evict_to_free == 0) {
itemstats[id].outofmemory++;
return NULL;
}
/*
* try to get one off the right LRU
* don't necessariuly unlink the tail because it may be locked: refcount>0
* search up from tail an item with refcount==0 and unlink it; give up after 50
* tries
*/
if (tails[id] == 0) {
itemstats[id].outofmemory++;
return NULL;
}
for (search = tails[id]; tries > 0 && search != NULL; tries--, search=search->prev) {
if (search->refcount == 0) {
if (search->exptime == 0 || search->exptime > current_time) {
itemstats[id].evicted++;
itemstats[id].evicted_time = current_time - search->time;
STATS_LOCK();
stats.evictions++;
STATS_UNLOCK();
#ifdef USE_REPLICATION
replication_call_del(ITEM_key(search), search->nkey);
#endif /* USE_REPLICATION */
}
do_item_unlink(search);
break;
}
}
it = slabs_alloc(ntotal, id);
if (it == 0) {
itemstats[id].outofmemory++;
/* Last ditch effort. There is a very rare bug which causes
* refcount leaks. We've fixed most of them, but it still happens,
* and it may happen in the future.
* We can reasonably assume no item can stay locked for more than
* three hours, so if we find one in the tail which is that old,
* free it anyway.
*/
tries = 50;
for (search = tails[id]; tries > 0 && search != NULL; tries--, search=search->prev) {
if (search->refcount != 0 && search->time + 10800 < current_time) {
itemstats[id].tailrepairs++;
search->refcount = 0;
do_item_unlink(search);
break;
}
}
it = slabs_alloc(ntotal, id);
if (it == 0) {
return NULL;
}
}
}
assert(it->slabs_clsid == 0);
it->slabs_clsid = id;
assert(it != heads[it->slabs_clsid]);
it->next = it->prev = it->h_next = 0;
it->refcount = 1; /* the caller will have a reference */
DEBUG_REFCNT(it, '*');
it->it_flags = 0;
it->nkey = nkey;
it->nbytes = nbytes;
strcpy(ITEM_key(it), key);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}
/*@null@*/
item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_time_t exptime, const int nbytes) {
uint8_t nsuffix;
item *it;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
it = slabs_alloc(ntotal);
if (it == 0) {
int tries = 50;
item *search;
/* If requested to not push old items out of cache when memory runs out,
* we're out of luck at this point...
*/
if (settings.evict_to_free == 0) return NULL;
/*
* try to get one off the right LRU
* don't necessariuly unlink the tail because it may be locked: refcount>0
* search up from tail an item with refcount==0 and unlink it; give up after 50
* tries
*/
if (id > LARGEST_ID) return NULL;
if (tails[id] == 0) return NULL;
for (search = tails[id]; tries > 0 && search != NULL; tries--, search=search->prev) {
if (search->refcount == 0) {
if (search->exptime == 0 || search->exptime > current_time) {
STATS_LOCK();
stats.evictions++;
STATS_UNLOCK();
}
do_item_unlink(search);
break;
}
}
it = slabs_alloc(ntotal);
if (it == 0) return NULL;
}
assert(it->slabs_clsid == 0);
it->slabs_clsid = id;
assert(it != heads[it->slabs_clsid]);
it->next = it->prev = it->h_next = 0;
it->refcount = 1; /* the caller will have a reference */
DEBUG_REFCNT(it, '*');
it->it_flags = 0;
it->nkey = nkey;
it->nbytes = nbytes;
strcpy(ITEM_key(it), key);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}
/*@null@*/
item *do_item_alloc(char *key, const size_t nkey, const int flags,
const rel_time_t exptime, const int nbytes,
const uint32_t cur_hv) {
uint8_t nsuffix;
item *it = NULL;
char suffix[40];
//计算这个item的空间
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
//根据大小判断从属于哪个slab
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
mutex_lock(&cache_lock);
/* do a quick check if we have any expired items in the tail.. */
//在LRU中尝试5次还没合适的空间，则执行申请空间的操作
int tries = 5;
int tried_alloc = 0;
item *search;
void *hold_lock = NULL;
rel_time_t oldest_live = settings.oldest_live;
search = tails[id];
/* We walk up *only* for locked items. Never searching for expired.
* Waste of CPU for almost all deployments */
for (; tries > 0 && search != NULL; tries--, search=search->prev) {
uint32_t hv = hash(ITEM_key(search), search->nkey, 0);
/* Attempt to hash item lock the "search" item. If locked, no
* other callers can incr the refcount
*/
/* FIXME: I think we need to mask the hv here for comparison? */
if (hv != cur_hv && (hold_lock = item_trylock(hv)) == NULL)
continue;
/* Now see if the item is refcount locked */
if (refcount_incr(&search->refcount) != 2) {
refcount_decr(&search->refcount);
/* Old rare bug could cause a refcount leak. We haven't seen
* it in years, but we leave this code in to prevent failures
* just in case */
if (search->time + TAIL_REPAIR_TIME < current_time) {
itemstats[id].tailrepairs++;
search->refcount = 1;
do_item_unlink_nolock(search, hv);
}
if (hold_lock)
item_trylock_unlock(hold_lock);
continue;
}
/* Expired or flushed */
// search指向的item过期了，则直接复用这块内存
if ((search->exptime != 0 && search->exptime < current_time)
|| (search->time <= oldest_live && oldest_live <= current_time)) {
itemstats[id].reclaimed++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
itemstats[id].expired_unfetched++;
}
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
do_item_unlink_nolock(it, hv);
/* Initialize the item block: */
it->slabs_clsid = 0;
}
//此刻，过期失效的item没有找到，申请内存又失败了。看来只能使用
//LRU淘汰一个item(即使这个item并没有过期失效)
else if ((it = slabs_alloc(ntotal, id)) == NULL) {
tried_alloc = 1;
if (settings.evict_to_free == 0) {
itemstats[id].outofmemory++;
} else {
itemstats[id].evicted++;
itemstats[id].evicted_time = current_time - search->time;
if (search->exptime != 0)
itemstats[id].evicted_nonzero++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
itemstats[id].evicted_unfetched++;
}
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
do_item_unlink_nolock(it, hv);
/* Initialize the item block: */
it->slabs_clsid = 0;
/* If we've just evicted an item, and the automover is set to
* angry bird mode, attempt to rip memory into this slab class.
* TODO: Move valid object detection into a function, and on a
* "successful" memory pull, look behind and see if the next alloc
* would be an eviction. Then kick off the slab mover before the
* eviction happens.
*/
if (settings.slab_automove == 2)
slabs_reassign(-1, id);
}
}
refcount_decr(&search->refcount);
/* If hash values were equal, we don't grab a second lock */
if (hold_lock)
item_trylock_unlock(hold_lock);
break;
}
//从slab分配器中申请内存
if (!tried_alloc && (tries == 0 || search == NULL))
it = slabs_alloc(ntotal, id);
if (it == NULL) {
itemstats[id].outofmemory++;
mutex_unlock(&cache_lock);
return NULL;
}
assert(it->slabs_clsid == 0);
assert(it != heads[id]);
/* Item initialization can happen outside of the lock; the item's already
* been removed from the slab LRU.
*/
it->refcount = 1; /* the caller will have a reference */
mutex_unlock(&cache_lock);
it->next = it->prev = it->h_next = 0;
it->slabs_clsid = id;
DEBUG_REFCNT(it, '*');
it->it_flags = settings.use_cas ? ITEM_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
memcpy(ITEM_key(it), key, nkey);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}
/*@null@*/
item *do_item_alloc(char *key, const size_t nkey, const int flags,
const rel_time_t exptime, const int nbytes,
const uint32_t cur_hv) {
uint8_t nsuffix;
item *it = NULL;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
mutex_lock(&cache_lock);
/* do a quick check if we have any expired items in the tail.. */
int tries = 5;
/* Avoid hangs if a slab has nothing but refcounted stuff in it. */
int tries_lrutail_reflocked = 1000;
int tried_alloc = 0;
item *search;
item *next_it;
void *hold_lock = NULL;
rel_time_t oldest_live = settings.oldest_live;
search = tails[id];
/* We walk up *only* for locked items. Never searching for expired.
* Waste of CPU for almost all deployments */
for (; tries > 0 && search != NULL; tries--, search=next_it) {
/* we might relink search mid-loop, so search->prev isn't reliable */
next_it = search->prev;
if (search->nbytes == 0 && search->nkey == 0 && search->it_flags == 1) {
/* We are a crawler, ignore it. */
tries++;
continue;
}
uint32_t hv = hash(ITEM_key(search), search->nkey);
/* Attempt to hash item lock the "search" item. If locked, no
* other callers can incr the refcount
*/
/* Don't accidentally grab ourselves, or bail if we can't quicklock */
if (hv == cur_hv || (hold_lock = item_trylock(hv)) == NULL)
continue;
/* Now see if the item is refcount locked */
if (refcount_incr(&search->refcount) != 2) {
/* Avoid pathological case with ref'ed items in tail */
do_item_update_nolock(search);
tries_lrutail_reflocked--;
tries++;
refcount_decr(&search->refcount);
itemstats[id].lrutail_reflocked++;
/* Old rare bug could cause a refcount leak. We haven't seen
* it in years, but we leave this code in to prevent failures
* just in case */
if (settings.tail_repair_time &&
search->time + settings.tail_repair_time < current_time) {
itemstats[id].tailrepairs++;
search->refcount = 1;
do_item_unlink_nolock(search, hv);
}
if (hold_lock)
item_trylock_unlock(hold_lock);
if (tries_lrutail_reflocked < 1)
break;
continue;
}
/* Expired or flushed */
if ((search->exptime != 0 && search->exptime < current_time)
|| (search->time <= oldest_live && oldest_live <= current_time)) {
itemstats[id].reclaimed++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
itemstats[id].expired_unfetched++;
}
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
do_item_unlink_nolock(it, hv);
/* Initialize the item block: */
it->slabs_clsid = 0;
} else if ((it = slabs_alloc(ntotal, id)) == NULL) {
tried_alloc = 1;
if (settings.evict_to_free == 0) {
itemstats[id].outofmemory++;
} else {
itemstats[id].evicted++;
itemstats[id].evicted_time = current_time - search->time;
if (search->exptime != 0)
itemstats[id].evicted_nonzero++;
if ((search->it_flags & ITEM_FETCHED) == 0) {
itemstats[id].evicted_unfetched++;
}
shadow_item* new_shadow_it = create_shadow_item(search);
hv = hash(new_shadow_it->key, new_shadow_it->nkey);
shadow_assoc_insert(new_shadow_it, hv);
insert_shadowq_item(new_shadow_it,new_shadow_it->slabs_clsid);
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
do_item_unlink_nolock(it, hv);
/* Initialize the item block: */
it->slabs_clsid = 0;
/* If we've just evicted an item, and the automover is set to
* angry bird mode, attempt to rip memory into this slab class.
* TODO: Move valid object detection into a function, and on a
* "successful" memory pull, look behind and see if the next alloc
* would be an eviction. Then kick off the slab mover before the
* eviction happens.
*/
if (settings.slab_automove == 2)
slabs_reassign(-1, id);
}
}
refcount_decr(&search->refcount);
/* If hash values were equal, we don't grab a second lock */
if (hold_lock)
item_trylock_unlock(hold_lock);
break;
}
if (!tried_alloc && (tries == 0 || search == NULL))
it = slabs_alloc(ntotal, id);
if (it == NULL) {
itemstats[id].outofmemory++;
mutex_unlock(&cache_lock);
return NULL;
}
assert(it->slabs_clsid == 0);
assert(it != heads[id]);
/* Item initialization can happen outside of the lock; the item's already
* been removed from the slab LRU.
*/
it->refcount = 1; /* the caller will have a reference */
mutex_unlock(&cache_lock);
it->next = it->prev = it->h_next = 0;
it->slabs_clsid = id;
DEBUG_REFCNT(it, '*');
it->it_flags = settings.use_cas ? ITEM_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
memcpy(ITEM_key(it), key, nkey);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}
/* 从 slab 系统分配一个空闲 item */
item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_time_t exptime, const int nbytes,
const uint32_t cur_hv)
{
uint8_t nsuffix;
item *it = NULL;
char suffix[40];
size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
if (settings.use_cas) {
ntotal += sizeof(uint64_t);
}
unsigned int id = slabs_clsid(ntotal);
if (id == 0)
return 0;
mutex_lock(&cache_lock);
/* do a quick check if we have any expired items in the tail.. */
int tries = 5;
int tried_alloc = 0;
item *search;
void *hold_lock = NULL;
rel_time_t oldest_live = settings.oldest_live;
search = tails[id];
/* We walk up *only* for locked items. Never searching for expired.
* Waste of CPU for almost all deployments */
for (; tries > 0 && search != NULL; tries--, search=search->prev)
{
uint32_t hv = hash(ITEM_key(search), search->nkey, 0);
/* Attempt to hash item lock the "search" item. If locked, no
* other callers can incr the refcount
*/
/* FIXME: I think we need to mask the hv here for comparison? */
if (hv != cur_hv && (hold_lock = item_trylock(hv)) == NULL)
continue;
/* Now see if the item is refcount locked */
if (refcount_incr(&search->refcount) != 2)
{
refcount_decr(&search->refcount);
/* Old rare bug could cause a refcount leak. We haven't seen
* it in years, but we leave this code in to prevent failures
* just in case */
if (search->time + TAIL_REPAIR_TIME < current_time)
{
itemstats[id].tailrepairs++;
search->refcount = 1;
do_item_unlink_nolock(search, hv);
}
if (hold_lock)
item_trylock_unlock(hold_lock);
continue;
}
/* 先检查 LRU 队列最后一个 item 是否超时, 超时的话就把这个 item 分配给用户 */
if ((search->exptime != 0 && search->exptime < current_time)
|| (search->time <= oldest_live && oldest_live <= current_time))
{
itemstats[id].reclaimed++;
if ((search->it_flags & ITEM_FETCHED) == 0)
{
itemstats[id].expired_unfetched++;
}
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
/* 把这个 item 从 LRU 队列和哈希表中移除 */
do_item_unlink_nolock(it, hv);
/* Initialize the item block: */
it->slabs_clsid = 0;
}
/* 没有超时的item, 那就尝试从slabclass分配, 运气不好的话, 分配失败, 那就把 LRU 队列最后一个 item 剔除, 然后分配给用户 */
else if ((it = slabs_alloc(ntotal, id)) == NULL)
{
tried_alloc = 1;
if (settings.evict_to_free == 0)
{
itemstats[id].outofmemory++;//显示出的统计信息
}
else
{
itemstats[id].evicted++;//这个slab的分配失败次数加1，后面的分析统计信息的线程会用到这个统计信息
itemstats[id].evicted_time = current_time - search->time;//显示的统计信息
if (search->exptime != 0)
itemstats[id].evicted_nonzero++;
if ((search->it_flags & ITEM_FETCHED) == 0)
{
itemstats[id].evicted_unfetched++;
}
it = search;
slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);//不用请求新的item了，减少相关的统计信息
/* 把老的item从hash表和lru队列中删除 */
do_item_unlink_nolock(it, hv);
/* Initialize the item block: */
it->slabs_clsid = 0;
/* If we've just 回收 an item, and the automover is set to angry bird mode, attempt to rip memory into this
slab class. TODO: Move valid object detection into a function, and on a "successful" memory pull, look
behind and see if the next alloc would be an eviction. Then kick off the slab mover before the eviction
happens.可以看到如果slab_automove=2(默认是1)，这样会导致angry模式，就是只要分配失败了，马上就选择一个slab(旧的slagclass
释放的)，把这个slab移动到当前slab-class中（不会有通过统计信息有选择的移动slab）*/
if (settings.slab_automove == 2)
slabs_reassign(-1, id);
}
}
refcount_decr(&search->refcount);
/* If hash values were equal, we don't grab a second lock */
if (hold_lock)
item_trylock_unlock(hold_lock);
break;
}
if (!tried_alloc && (tries == 0 || search == NULL)) it = slabs_alloc(ntotal, id);
if (it == NULL)
{
itemstats[id].outofmemory++;
mutex_unlock(&cache_lock);
return NULL;
}
assert(it->slabs_clsid == 0);
assert(it != heads[id]);
/* Item initialization can happen outside of the lock; the item's already been removed from the slab LRU. */
it->refcount = 1; /* the caller will have a reference */
mutex_unlock(&cache_lock);
it->next = it->prev = it->h_next = 0;
it->slabs_clsid = id;
DEBUG_REFCNT(it, '*');
it->it_flags = settings.use_cas ? ITEM_CAS : 0;
it->nkey = nkey;
it->nbytes = nbytes;
memcpy(ITEM_key(it), key, nkey);
it->exptime = exptime;
memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
it->nsuffix = nsuffix;
return it;
}