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Date: 十月 13, 2016

“Page out”和“swap out”

下文摘自Linux performance and tuning guidelines

The pages are used mainly for two purposes: page cache and process address space. The page cache is pages mapped to a file on disk. The pages that belong to a process address space (called anonymous memory because it is not mapped to any files, and it has no name) are used for heap and stack. When kswapd reclaims pages, it would rather shrink the page cache than page out (or swap out) the pages owned by processes. A large proportion of page cache that is reclaimed and process address space that is reclaimed might depend on the usage scenario and will affect performance. You can take some control of this behavior by using /proc/sys/vm/swappiness.

Page out and swap out: The phrases “page out” and “swap out” are sometimes confusing. The phrase “page out” means take some pages (a part of entire address space) into swap space while “swap out” means taking entire address space into swap space. They are sometimes used interchangeably.

Unix中的zombie进程和orphan进程

Unix中子进程退出后,如果父进程没有使用wait()函数获得子进程的退出状态,则子进程的相关信息仍然会在系统的进程表里占用一席之地,这时的子进程称之为zombie进程。如果父进程先于子进程退出,这时的子进程称之为orphan进程,而init进程则会变成orphan进程的父进程。init进程会定期处理父进程是initzombie进程。

参考资料:
Zombie process
Zombie process vs Orphan process

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