读《情景分析》之swap_out时的不解，非常不解。
面程序片断摘自2.4.0源代码(mm/vmscan.c)，末尾的if与else中都有'break'，即不论best为何值都要求break（执行goto select也不行啊）而跳出循环,这样外层FOR还有作用么？mm->swap_cnt和RSS的作用和关系也写得不太清楚，望大虾指教！小弟先行谢过！！
附：swap_out
/*
* Select the task with maximal swap_cnt and try to swap out a page.
* N.B. This function returns only 0 or 1. Return values != 1 from
* the lower level routines result in continued processing.
*/
#define SWAP_SHIFT 5
#define SWAP_MIN 8
static int swap_out(unsigned int priority, int gfp_mask)
{
int counter;
int __ret = 0;
/*
* We make one or two passes through the task list, indexed by
* assign = {0, 1}:
* Pass 1: select the swappable task with maximal RSS that has
* not yet been swapped out.
* Pass 2: re-assign rss swap_cnt values, then select as above.
*
* With this approach, there's no need to remember the last task
* swapped out. If the swap-out fails, we clear swap_cnt so the
* task won't be selected again until all others have been tried.
*
* Think of swap_cnt as a "shadow rss" - it tells us which process
* we want to page out (always try largest first).
*/
counter = (nr_threads << SWAP_SHIFT) >> priority;
if (counter < 1)
counter = 1;
for (; counter >= 0; counter--) {
struct list_head *p;
unsigned long max_cnt = 0;
struct mm_struct *best = NULL;
int assign = 0;
int found_task = 0;
select:
spin_lock(&mmlist_lock);
p = init_mm.mmlist.next;
for (; p != &init_mm.mmlist; p = p->next) {
struct mm_struct *mm = list_entry(p, struct mm_struct, mmlist);
if (mm->rss <= 0)
continue;
found_task++;
/* Refresh swap_cnt? */
if (assign == 1) {
mm->swap_cnt = (mm->rss >> SWAP_SHIFT);
if (mm->swap_cnt < SWAP_MIN)
mm->swap_cnt = SWAP_MIN;
}
if (mm->swap_cnt > max_cnt) {
max_cnt = mm->swap_cnt;
best = mm;
}
}
/* Make sure it doesn't disappear */
if (best)
atomic_inc(&best->mm_users);
spin_unlock(&mmlist_lock);
/*
* We have dropped the tasklist_lock, but we
* know that "mm" still exists: we are running
* with the big kernel lock, and exit_mm()
* cannot race with us.
*/
if (!best) {
if (!assign && found_task > 0) {
assign = 1;
goto select;
}
break;
} else {
__ret = swap_out_mm(best, gfp_mask);
mmput(best);
break;
}
}
return __ret;
}
问题点数：100、回复次数：3Top
1 楼mz_1984（）回复于 2006-11-06 13:34:08 得分 0
哎，好伤心哪。Top
2 楼xiangqian（天阁流云）回复于 2006-11-06 19:05:04 得分 0
不是还有continue么Top
3 楼mz_1984（）回复于 2006-11-09 11:44:22 得分 0
进continue 是有条件的，条件不满足就不会continue，执行到最后就是那个IF{ 。。break;}ELSE{...break;}了。Top
