网络子系统53_ip协议分片重组_内存阈值

//调用路径：ip_defrag->ip_evictor//分片重组时，可使用内存上下限：//1.sysctl_ipfrag_high_thresh 可用内存上限//2.sysctl_ipfrag_low_thresh 内存超过上限后，需要释放内存到此限1.1 static void ip_evictor(void){struct ipq *qp;struct list_head *tmp;int work;//计算需要释放的内存work = atomic_read(&ip_frag_mem) - sysctl_ipfrag_low_thresh;if (work <= 0)return;while (work > 0) {read_lock(&ipfrag_lock);if (list_empty(&ipq_lru_list)) {//最近最久没有没有被使用的链表，链表头的ipq最久没有被使用read_unlock(&ipfrag_lock);return;}//在获取锁的情况下，释放ipqtmp = ipq_lru_list.next;qp = list_entry(tmp, struct ipq, lru_list);atomic_inc(&qp->refcnt);//增加ipq的引用计数，防止其突然消失read_unlock(&ipfrag_lock);spin_lock(&qp->lock);if (!(qp->last_in&COMPLETE))//ipq没有接收完全ipq_kill(qp);//spin_unlock(&qp->lock);ipq_put(qp, &work);IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);}}//调用路径：ip_evictor->ipq_kill1.2 static void ipq_kill(struct ipq *ipq){if (del_timer(&ipq->timer))//删除ipq的定时器atomic_dec(&ipq->refcnt);//递减定时器持有的引用计数if (!(ipq->last_in & COMPLETE)) {//ipq没有接收完全ipq_unlink(ipq);//将ipq从ipq hash表bucket的链表上摘下来atomic_dec(&ipq->refcnt);//递减ipq hash表bucket对其持有的引用计数ipq->last_in |= COMPLETE;//标记ipq接收完全，防止其被更新}}1.3 static __inline__ void ipq_put(struct ipq *ipq, int *work){if (atomic_dec_and_test(&ipq->refcnt))//递减在ip_evictor中对ipq的引用ip_frag_destroy(ipq, work);//释放关联到此ipq的skb}1.4 static void ip_frag_destroy(struct ipq *qp, int *work){struct sk_buff *fp;//此ipq接收到的所有分片fp = qp->fragments;while (fp) {struct sk_buff *xp = fp->next;frag_kfree_skb(fp, work);//释放skb，从work中减去此skb的大小fp = xp;}frag_free_queue(qp, work);//释放ipq结构}