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引言
Memcached，作為一款高機能的分散式內存緩存體系，在減輕材料庫負載、晉升Web伺服器機能方面發揮側重要感化。其內存管理戰略是Memcached高效運轉的關鍵。本文將深刻剖析Memcached的內存管理機制，包含Slab Allocation、內存碎片處理、緩存優化戰略等，並供給實戰技能。
Memcached內存管理概述
Memcached的內存管理重要依附於Slab Allocation機制，該機制將內存分割成多個slab，每個slab包含多個牢固大小的chunk，以存儲差別大小的數據項。這種計劃旨在增加內存碎片，進步內存利用率。
Slab Allocation機制
Slab Class
Memcached將內存分別為多個slab class，每個class包含雷同大小的chunk。chunk的大小根據數據項的大小停止分別，以增加內存碎片。
#define SLABCLASS_SLABCLASSNAME(slabclass) (slabclass->name)
#define SLABCLASS_SIZE(slabclass) (slabclass->size)
Slab Class分配
Memcached根據數據項的大小抉擇合適的slab class停止分配。假如數據項大小與某個slab class的chunk大小不婚配，則抉擇最瀕臨的slab class。
slabclass_t *slabs_get(slabclass_t *s) {
assert(s);
assert(s->size > 0);
assert(s->limit > 0);
assert(s->num < s->limit);
return s;
}
Slab Class開釋
當數據項從緩存中刪除時，Memcached會將其開釋回對應的slab class。
”`c void item_return_to_slab(item *it) {
assert(it);
assert(it->slabslab);
assert(it->size <= it->slabslab->size);
assert(it->size > 0);
assert(it->slabslab->slabs);
assert(it->slabslab->slabs[it->slabslab->num]);
assert(it->slabslab->slabs[it->slabslab->num]->slabs);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num