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slab系统初始化过程中，待所有cpu都完成初始化后，通过调用kmem_cache_init_late来函数完善cache_chain上每个struct kmem_cache实例的cpu缓存机制（包括cpu本地高速缓存和每个节点上的cpu共享缓存shared cache）
kmem_cache_init_late() |---list_for_each_entry(cachep, &slab_caches, list)//遍历slab_caches全局链表中每个struct kmem_cache实例 enable_cpucache(cachep, GFP_NOWAIT)//对每个struct kmem_cache实例缓存机制进行完善 |--->cache_random_seq_create()//初始化struct kmem_cache实例num成员 |--->计算并设置struct kmem_cache实例的limit,batchcount,shared成员 |--->do_tune_cpucache()//struct kmem_cache实例缓存机制的完善和其node成员数组中数组项的初始化 |--->__do_tune_cpucache() |--->alloc_kmem_cache_cpus()//分配新的本地高速缓存区域（从Per_cpu area分配） |--->将kmem_cache实例的cpu_cache指向新分配的本地高速缓存区域（Per_CPU内存空间） |---for_each_online_cpu(cpu)//遍历每个cpu free_block()//释放对应cpu旧的本地缓存中缓存的slab obj到对应的slab链表中 |--->free_percpu()//释放旧的Per_CPU变量，struct kmem_cache实例的高速缓存cpu_cache |--->setup_kmem_cache_nodes()//初始化node数组中每个kmem_cache_nod实例（共享缓存区域 更新和相关成员初始化） |---for_each_online_node(node)//遍历每个内存节点 setup_kmem_cache_node()//对kmem_cache_nod实例进初始化 |--->alloc_arraycache()//为当前节点共享缓存区域分配空间 |--->将kmem_cache_node实例的shared成员指向新分配的共享缓存空间 |--->init_cache_node()//初始化kmem_cache_node实例的的3个slab链 表等
// mm/slab.c/* *1.完善全局链表slab_caches上所有struct kmem_cache实例的缓存机制: * 根据slab obj大小，给本地cpu高速缓存和每个节点shared cache重新分配内存空间，并释放旧缓存缓存的 * slab obj（free_block）和旧缓存本身(kfree)） *2.初始化全局链表slab_caches上所有struct kmem_cache实例的node数组中每个struct kmem_cache_node实例的 * 相关数据（主要是每个内存节点中3种类型slab 链表的初始化） */void __init kmem_cache_init_late(void){ struct kmem_cache *cachep; slab_state = UP; /* 6) resize the head arrays to their final sizes */ mutex_lock(&slab_mutex); //遍历slab_caches上所有的slab cache描述符（struct kmem_cache结构体实例） list_for_each_entry(cachep, &slab_caches, list) /* *完善当前slab cache描述符的cpu高速缓存机制，并对slab cache描述符的node成员中的每个struct kmem_cache_node *实例进行初始化操作. *1.对本地cpu高速缓存（cachep->cpu_cache）,通过slab obj的大小重新计算array_cache每个成员的 * 值，然后为每个cpu重新分配一个array_cache实例（每cpu变量），并替换旧的arry_cache。 *2.若是NUMA结构，完善cpu共享高速缓存机制（分配足够的共享array_cache实例并完成地址关联）. *3.为slab cache描述符每个节点对应的struct kmem_cache_node实例的相关成员进行初始化操作，主要是完成3个 * slab链表的初始化 */ if (enable_cpucache(cachep, GFP_NOWAIT)) BUG(); mutex_unlock(&slab_mutex); /* Done! */ slab_state = FULL;#ifdef CONFIG_NUMA /* * Register a memory hotplug callback that initializes and frees * node. * */ hotplug_memory_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);#endif /* * The reap timers are started later, with a module init call: That part * of the kernel is not yet operational. */} /* Called with slab_mutex held always */static int enable_cpucache(struct kmem_cache *cachep, gfp_t gfp){ int err; int limit = 0; int shared = 0; int batchcount = 0; // err = cache_random_seq_create(cachep, cachep->num, gfp); if (err) goto end; //判断该slab cache描述符是否属于某一个memcg组，是的画，用该组root节点对应的数据进行初始化 if (!is_root_cache(cachep)) { struct kmem_cache *root = memcg_root_cache(cachep); limit = root->limit; shared = root->shared; batchcount = root->batchcount; } //找到memcg组，直接完成了初始化设置，不许要根据obj大小进行成员值预估 if (limit && shared && batchcount) goto skip_setup; /* * The head array serves three purposes: * - create a LIFO ordering, i.e. return objects that are cache-warm * - reduce the number of spinlock operations. * - reduce the number of linked list operations on the slab and * bufctl chains: array operations are cheaper. * The numbers are guessed, we should auto-tune as described by * Bonwick. */ // 根据对象(slab obj)的大小计算local cache中对象的数量 if (cachep->size > 131072) limit = 1; else if (cachep->size > PAGE_SIZE) limit = 8; else if (cachep->size > 1024) limit = 24; else if (cachep->size > 256) limit = 54; else limit = 120; /* * CPU bound tasks (e.g. network routing) can exhibit cpu bound * allocation behaviour: Most allocs on one cpu, most free operations * on another cpu. For these cases, an efficient object passing between * cpus is necessary. This is provided by a shared array. The array * replaces Bonwick's magazine layer. * On uniprocessor, it's functionally equivalent (but less efficient) * to a larger limit. Thus disabled by default. * 多核下设置共享本地缓存实例的个数（struct kmem_cache的shared成员），该slab描述符每个节点的共享缓存中最大 * obj数量为cachep->shared*batchcount */ shared = 0; if (cachep->size <= PAGE_SIZE && num_possible_cpus() > 1) shared = 8; batchcount = (limit + 1) / 2;skip_setup: /* *根据前面计算出的limit, batchcount, shared值，为当前slab cache缓存更新本地cpu高速缓存和设置共享cpu高速缓存 */ err = do_tune_cpucache(cachep, limit, batchcount, shared, gfp);end: if (err) pr_err("enable_cpucache failed for %s, error %d\n", cachep->name, -err); return err;} /* *(1)设置slab cache描述符的本地cpu高速缓存cpu_cache（每cpu变量，是个数组，数组中每个元素对应每个cpu）: * struct kmem_cache的cpu_caches数组中的每个成员需要更新成根据slab obj实际大小计算出来的新struct * array_cache实例，同时将旧的固定大小的struct array_cache释放 *(2)设置slab cache描述符的共享cpu高速缓存： * a.设置struct kmem_cache的shared值 * b.设置struct kmem_cache的node数组成员中每个struct kmem_cache_node对应节点上的cpu共享缓存数组. * 就是跟给该slab cache缓存对应的每个节点分配足够多的struct arrary_cache实例 * c.设置struct kmem_cache的node数组成员中每个struct kmem_cache_node实例对应节点的3个slab链表 */static int do_tune_cpucache(struct kmem_cache *cachep, int limit, int batchcount, int shared, gfp_t gfp){ int ret; struct kmem_cache *c; ret = __do_tune_cpucache(cachep, limit, batchcount, shared, gfp); if (slab_state < FULL) return ret; if ((ret < 0) || !is_root_cache(cachep)) return ret; lockdep_assert_held(&slab_mutex); for_each_memcg_cache(c, cachep) { /* return value determined by the root cache only */ __do_tune_cpucache(c, limit, batchcount, shared, gfp); } return ret;} static int __do_tune_cpucache(struct kmem_cache *cachep, int limit, int batchcount, int shared, gfp_t gfp){ struct array_cache __percpu *cpu_cache, *prev; int cpu; // 根据limit, batchcount数值，为每个cpu构建新的array_cache实例并存储在cpu_cache数组 cpu_cache = alloc_kmem_cache_cpus(cachep, limit, batchcount); if (!cpu_cache) return -ENOMEM; //旧的固定大小的array_cache实例数组 prev = cachep->cpu_cache; //将根据slab obj大小计算出来的新本地cpu高速缓存赋值给slab cache描述符的cpu_cache成员 cachep->cpu_cache = cpu_cache; //各个cpu上的每cpu变量数据同步（cachep->cpu_cache更新） kick_all_cpus_sync(); check_irq_on(); //更新该slab cache描述符中与本地cpu高速缓存有关的成员数据 cachep->batchcount = batchcount; cachep->limit = limit; cachep->shared = shared; if (!prev) goto setup_node; /* *此循环就是将旧的本地cpu高速缓存中缓存的slab obj释放给其slab系统.因为slab系统初始化时由于每个本地高 *速缓存对应的avail为0，所以此处可被忽略。 */ for_each_online_cpu(cpu) { LIST_HEAD(list); int node; struct kmem_cache_node *n; struct array_cache *ac = per_cpu_ptr(prev, cpu); node = cpu_to_mem(cpu); n = get_node(cachep, node); spin_lock_irq(&n->list_lock); free_block(cachep, ac->entry, ac->avail, node, &list); spin_unlock_irq(&n->list_lock); slabs_destroy(cachep, &list); } //将旧的cpu本地高速缓存这一Per_CPU变量释放（释放到每个cpu的Per_CPU area） free_percpu(prev);setup_node: return setup_kmem_cache_nodes(cachep, gfp);//分配lab cache描述每个节点对应的共享缓存区域，然后将每个节点对 应的struct kmem_cache_node实例成员进行初始化。} // mm/slab.c/*This initializes kmem_cache_node or resizes various caches for all nodes*/static int setup_kmem_cache_nodes(struct kmem_cache *cachep, gfp_t gfp){ ...... //遍历每个节点，并给每个节点的本地cpu高速缓存进行更新 for_each_online_node(node) { ret = setup_kmem_cache_node(cachep, node, gfp, true); } ......}/* *给slab cache描述符node数组成员中的每个struct kmem_cache_node实例进行初始化，主要工作： * 1.共享高速缓存shared成员进行内存空间分配（缓存的entry数组长度cachep->shared*cachep->batchcount） * 2.3种类型slab链表的初始化。 */static int setup_kmem_cache_node(struct kmem_cache *cachep, int node, gfp_t gfp, bool force_change){ int ret = -ENOMEM; struct kmem_cache_node *n; struct array_cache *old_shared = NULL; struct array_cache *new_shared = NULL; struct alien_cache **new_alien = NULL; LIST_HEAD(list); if (use_alien_caches) { new_alien = alloc_alien_cache(node, cachep->limit, gfp); if (!new_alien) goto fail; } //多cpu，slab cache描述符需要给每个内存节点分配一个共享cpu缓存区域 if (cachep->shared) { /* *每个节点分配的共享缓存区域最多能缓存cachep->shared * cachep->batchcount个slab obj，分配对应空间，并 *将虚拟地址记录到new_shared上 */ new_shared = alloc_arraycache(node, cachep->shared * cachep->batchcount, 0xbaadf00d, gfp); if (!new_shared) goto fail; } /* *1.对本slab cache描述符node数组成员中每个struct kmem_cache_node实例的free_limit成员进行初始化（ * free_limit表示该slab cache描述在对应节点中空闲obj的数量上限，超过该值就会将一定数量的slab obj释放到伙 * 伴系统的空闲链表中） *2.对本slab cache描述符node数组成员中每个struct kmem_cache_node实例的3个类型slab链表进行初始化。 */ ret = init_cache_node(cachep, node, gfp); if (ret) goto fail; //获取本slab cache描述符cachep对应节点node的struct kmem_cache_node的描述符 n = get_node(cachep, node); spin_lock_irq(&n->list_lock); /* *释放slab cache描述符管理的每个内存节点旧的cpu共享高速缓存中缓存的slab obj,释放到对应的slab链表中，就是释放 *n->shared->entry数组中每个数组项指向的slab obj对象. */ if (n->shared && force_change) { free_block(cachep, n->shared->entry, n->shared->avail, node, &list); n->shared->avail = 0; } /* *将新新分配并初始化的共享cpu缓存空间赋值给slab描述符对应节点的struct kmem_cache_node实例的shared成 *员 */ if (!n->shared || force_change) { old_shared = n->shared; n->shared = new_shared; new_shared = NULL; } if (!n->alien) { n->alien = new_alien; new_alien = NULL; } spin_unlock_irq(&n->list_lock); slabs_destroy(cachep, &list); /* * To protect lockless access to n->shared during irq disabled context. * If n->shared isn't NULL in irq disabled context, accessing to it is * guaranteed to be valid until irq is re-enabled, because it will be * freed after synchronize_sched(). */ if (old_shared && force_change) synchronize_sched();fail: //收尾工作释放旧的struct array_cache(释放到对应slab系统的本地高速缓存中) kfree(old_shared); kfree(new_shared); free_alien_cache(new_alien); return ret;} ps：
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