slub释放过程do_slab_free

do_slab_free

一、快速路径

if (likely(page &＃61;&＃61; c->page)) {void **freelist &＃61; READ_ONCE(c->freelist);set_freepointer(s, tail_obj, freelist);if (unlikely(!this_cpu_cmpxchg_double(s->cpu_slab->freelist, s->cpu_slab->tid,freelist, tid,head, next_tid(tid)))) {note_cmpxchg_failure("slab_free", s, tid);goto redo;}stat(s, FREE_FASTPATH);
} else__slab_free(s, page, head, tail_obj, cnt, addr);
1、要释放的对象正好在cpu本地缓存中&＃xff1b;
2、set_freepointer函数&＃xff1a;将要释放的object加入到空闲的object链表中&＃xff0c;并且为链表中代替freelist为第一个空闲的object&＃xff0c;即相当于object->next &＃61; c->freelist;
3、重新分配freelist&＃xff0c;这里是将c->freelist &＃61; head(head即目标object);

二、慢速路径

进入__slab_free函数&＃xff0c;大致框架如下&＃xff1a;

do {if (unlikely(n)) {spin_unlock_irqrestore(&n->list_lock, flags);n &＃61; NULL;}prior &＃61; page->freelist;counters &＃61; page->counters;set_freepointer(s, tail, prior);new.counters &＃61; counters;/** 1、frozen&＃61;0&＃xff0c;说明该slab在node中&＃xff1b;frozen&＃61;1&＃xff0c;则说明该slab在slab_cpu缓存中&＃xff1b;* 2、inuse&＃61;0&＃xff0c;说明该slab中没有正在使用的object&＃xff1b;inuse&＃61;objects&＃xff0c;则说明该slab为full* 3、prior&＃61;0&＃xff0c;说明目标object在c->page中或者在s->slab_cpu->partital、s->node->partital中且无可分配的object*/was_frozen &＃61; new.frozen;new.inuse -&＃61; cnt;/** 下面需要对目标object释放的情况进行划分&＃xff1a;* &＃xff08;1&＃xff09;inuse&＃61;0 && was_frozen&＃61;0&＃xff1a;目标object在node节点中&＃xff0c;且释放后该slab中的object 全部未分配&＃xff0c;此时该slab可以释放到伙伴系统或者不处理&＃xff1b;* &＃xff08;2&＃xff09;prior&＃61;0 && was_frozen&＃61;0&＃xff1a;释放前在full的slab链表中&＃xff0c;释放后为半满状态&＃xff1b;* &＃xff08;3&＃xff09;was_frozen&＃61;1&＃xff1a;该slab在s->slab_cpu->partital缓存中&＃xff1b;*/if ((!new.inuse || !prior) && !was_frozen) { //(1)(2)if (kmem_cache_has_cpu_partial(s) && !prior) { //(2)new.frozen &＃61; 1;} else { //(1)n &＃61; get_node(s, page_to_nid(page));spin_lock_irqsave(&n->list_lock, flags);}
} while (!cmpxchg_double_slab(s, page,prior, counters,head, new.counters,"__slab_free"));
/* * 前面的while循环中对目标object释放进行了分类和简单的预处理&＃xff0c;下面针对这几种情况进行后续的处理。* 包括是否将空的slab释放回伙伴系统以及维护slab_cpu->patital和node->partital链表&＃xff1b;*/if (likely(!n)) {if (new.frozen && !was_frozen) { //(2)node节点&＃xff0c;半满put_cpu_partial(s, page, 1);//将slab释放到slab_cpu->partital链表中stat(s, CPU_PARTIAL_FREE);}if (was_frozen) //slab_cpu->partital中&＃xff0c;则不处理直接返回stat(s, FREE_FROZEN);return;
}
//释放object后该slab变为free&＃xff0c;此时需要对比node->partital中slab的数量和内核定义的最小min大小
//如果n->nr_partial >&＃61; s->min_partial&＃xff0c;则将slab释放到伙伴系统&＃xff1b;
//如果n->nr_partial min_partial, 则不处理&＃xff1b;
if (unlikely(!new.inuse && n->nr_partial >&＃61; s->min_partial))goto slab_empty;//未定义CONFIG_SLUB_CPU_PARTITAL时走这个流程&＃xff1b;
if (!kmem_cache_has_cpu_partial(s) && unlikely(!prior)) {remove_full(s, n, page);//从full链表中移除add_partial(n, page, DEACTIVATE_TO_TAIL);//加入到node->partital链表中stat(s, FREE_ADD_PARTIAL);
}
spin_unlock_irqrestore(&n->list_lock, flags);
return;
slab_empty:if (prior) {/** Slab on the partial list.*/remove_partial(n, page);//将该slab从链表中删除&＃xff0c;并将nr_partital减一stat(s, FREE_REMOVE_PARTIAL);} else {/* Slab must be on the full list */remove_full(s, n, page);}spin_unlock_irqrestore(&n->list_lock, flags);stat(s, FREE_SLAB);discard_slab(s, page);
}

所以从代码来看&＃xff0c;主要分成以下几种情况&＃xff1a;

1、目标object在s->slab_cpu->partital中&＃xff0c;直接释放即可&＃xff0c;无需后续的处理&＃xff1b;

2、目标object在s->node中&＃xff0c;释放完object后slab中的object全为free&＃xff1b;此时需要考虑空的slab如何处理

&＃xff08;1&＃xff09;s->node->partital中slab的个数大于等于min_partital时&＃xff0c;将该slab释放到伙伴系统&＃xff1b;

&＃xff08;2&＃xff09;s->node->partital中slab的个数小于min_partital时&＃xff0c;该slab依然保留在s->node->partital链表中&＃xff1b;

3、目标object在s->node中&＃xff0c;释放object前slab为full&＃xff0c;没有可分配object&＃xff0c;释放完后为半满状态&＃xff1b;此时需要将半满的slab从full链表中删除并加入到s->slab_cpu的链表中&＃xff0c;需要注意s->slab_cpu->partital中也需要判断下所有的free的object的数量是否超过了规定的水位&＃xff0c;判断后在决定是否加入&＃xff1b;

lab从full链表中删除并加入到s->slab_cpu的链表中&＃xff0c;需要注意s->slab_cpu->partital中也需要判断下所有的free的object的数量是否超过了规定的水位&＃xff0c;判断后在决定是否加入&＃xff1b;