内存使用到多少时候开始使用swap ?

惜

60%

jjg6256308

应该是剩余60M 的时候开始使用！

zongjiezhe

高手才有心情研究这个啊，菜鸟看了也是白看，等用到的时候就忘了

jerryjzm

swap tendency = mapped ratio / 2 + distress + swappiness

The mapped ratio value is the percentage of pages in all memory zones that belong to User Mode address spaces (sc->nr_mapped) with respect to the total number of allocatable page frames. A high value of mapped_ratio means that the dynamic memory is mostly used by User Mode processes, while a low value means that it is mostly used by the page cache.

The distress value is a measure of how effectively the PFRA is reclaiming page frames in this zone; it is based on the scanning priority of the zone in the previous run of the PFRA, which is stored in the prev_priority field of the zone descriptor. The distress value depends on the zone's previous priority as follows:

Zone prev. priority
12...7
6
5
4
3
2
1
0

Distress value
0
1
3
6
12
25
50
100





Finally, the swappiness value is a user-defined constant, which is usually set to 60. The system administrator may tune this value by writing in the /proc/sys/vm/swappiness file or by issuing the proper sysctl( ) system call.

Pages will be reclaimed from the address spaces of processes only if the zone's swap tendency is greater than or equal to 100. Thus, if the system administrator sets swappiness to 0, then the PFRA never reclaims pages in the User Mode address spaces unless the zone's previous priority is zero (an unlikely event); if the administrator sets swappiness to 100, then the PFRA reclaims pages in the User Mode address spaces at every invocation.

swappiness，吃参数是得到swap tendency的一个量，而swap tendency是linux内核进行内存进行回收的一个阀值和标量。感觉和ls题目的说明还不尽相同

mfkwwgi

首先是,kswapd进程来定期扫描系统资源,查看内存是否够用,由两个值影响pages_high和page_low,如果现在可使用的区间在page_high<x<page_low,就开始检查从文件系统读入的文件,有无被修改的内存页面,如果有就写入到磁盘,但是,如果内存页面被修改了,有可能不是从文件系统读入的,即找不到回写的位置,如malloc产生的anonymous内存数据就写入swap分区,这部分当进程在次被唤醒,获得了CPU运行时间,在从swap读入;