mirror of
https://github.com/LCTT/TranslateProject.git
synced 2025-01-25 23:11:02 +08:00
translated
This commit is contained in:
LuMing
parent
8ae6c84d33
commit
6496db0616
@ -1,121 +0,0 @@
|
|||||||
[#]: collector: (lujun9972)
|
|
||||||
[#]: translator: (luuming)
|
|
||||||
[#]: reviewer: ( )
|
|
||||||
[#]: publisher: ( )
|
|
||||||
[#]: url: ( )
|
|
||||||
[#]: subject: (When to be concerned about memory levels on Linux)
|
|
||||||
[#]: via: (https://www.networkworld.com/article/3394603/when-to-be-concerned-about-memory-levels-on-linux.html)
|
|
||||||
[#]: author: (Sandra Henry-Stocker https://www.networkworld.com/author/Sandra-Henry_Stocker/)
|
|
||||||
|
|
||||||
When to be concerned about memory levels on Linux
|
|
||||||
======
|
|
||||||
Memory management on Linux systems is complicated. Seeing high usage doesn’t necessarily mean there’s a problem. There are other things you should also consider.
|
|
||||||
![Qfamily \(CC BY 2.0\)][1]
|
|
||||||
|
|
||||||
Running out of memory on a Linux system is generally _not_ a sign that there's a serious problem. Why? Because a healthy Linux system will cache disk activity in memory, basically gobbling memory that isn't being used, which is a very good thing.
|
|
||||||
|
|
||||||
In other words, it doesn't allow memory to go to waste. It uses the spare memory to increase disk access speed, and it does this _without_ taking memory away from running applications. This memory caching, as you might well imagine, is hundreds of times faster than working directly with the hard-disk drives (HDD) and significantly faster than solid-state drives. Full or near full memory normally means that a system is running as efficiently as it can — not that it's running into problems.
|
|
||||||
|
|
||||||
**[ Also see:[Must-know Linux Commands][2] ]**
|
|
||||||
|
|
||||||
### How caching works
|
|
||||||
|
|
||||||
Disk caching simply means that a system is taking advantage of unused resources (free memory) to speed up disk reads and writes. Applications don't lose anything and most of the time can acquire more memory whenever they need it. In addition, disk caching does not cause applications to resort to using swap. Instead, memory used for disk caching is always returned immediately when needed and disk content updated.
|
|
||||||
|
|
||||||
### Major and minor page faults
|
|
||||||
|
|
||||||
Linux systems allocate memory to processes by breaking physical memory into chunks called "pages" and then mapping those pages into process virtual memory. Pages that appear to no longer be used may be removed from memory — even if the related process is still running. When a process needs a page that is no longer mapped or no longer in memory, a fault is generated. So, "fault" does not mean "error" but instead means "unavailable," and faults play an important role in memory management.
|
|
||||||
|
|
||||||
A minor fault means the page is in memory but not allocated to the requesting process or not marked as present in the memory management unit. A major fault means the page in no longer in memory.
|
|
||||||
|
|
||||||
If you'd like to get a feel for how often minor and major page faults occur, try a **ps** command like this one. Note that we're asking for the fields related to page faults and the commands to be listed. Numerous lines were omitted from the output. The MINFL displays the number of minor faults, while MAJFL represents the number of major faults.
|
|
||||||
|
|
||||||
```
|
|
||||||
$ ps -eo min_flt,maj_flt,cmd
|
|
||||||
MINFL MAJFL CMD
|
|
||||||
230760 150 /usr/lib/systemd/systemd --switched-root --system --deserialize 18
|
|
||||||
0 0 [kthreadd]
|
|
||||||
0 0 [rcu_gp]
|
|
||||||
0 0 [rcu_par_gp]
|
|
||||||
0 0 [kworker/0:0H-kblockd]
|
|
||||||
...
|
|
||||||
166 20 gpg-agent --homedir /var/lib/fwupd/gnupg --use-standard-socket --daemon
|
|
||||||
525 1 /usr/libexec/gvfsd-trash --spawner :1.16 /org/gtk/gvfs/exec_spaw/0
|
|
||||||
4966 4 /usr/libexec/gnome-terminal-server
|
|
||||||
3617 0 bash
|
|
||||||
0 0 [kworker/1:0H-kblockd]
|
|
||||||
927 0 gdm-session-worker [pam/gdm-password]
|
|
||||||
```
|
|
||||||
|
|
||||||
To report on a single process, you might try a command like this:
|
|
||||||
|
|
||||||
```
|
|
||||||
$ ps -o min_flt,maj_flt 1
|
|
||||||
MINFL MAJFL
|
|
||||||
230064 150
|
|
||||||
```
|
|
||||||
|
|
||||||
You can also add other fields such as the process owner's UID and GID.
|
|
||||||
|
|
||||||
```
|
|
||||||
$ ps -o min_flt,maj_flt,cmd,args,uid,gid 1
|
|
||||||
MINFL MAJFL CMD COMMAND UID GID
|
|
||||||
230064 150 /usr/lib/systemd/systemd -- /usr/lib/systemd/systemd -- 0 0
|
|
||||||
```
|
|
||||||
|
|
||||||
### How full is full?
|
|
||||||
|
|
||||||
One way to get a better handle on how memory is being used is with the **free -m** command. The **-m** option reports the numbers in mebibytes (MiBs) instead of bytes.
|
|
||||||
|
|
||||||
```
|
|
||||||
$ free -m
|
|
||||||
total used free shared buff/cache available
|
|
||||||
Mem: 3244 3069 35 49 140 667
|
|
||||||
Swap: 3535 0 3535
|
|
||||||
```
|
|
||||||
|
|
||||||
Note that "free" (unused) memory can be running low while "available" (available for starting new applications) might report a larger number. The distinction between these two fields is well worth paying attention to. Available means that it can be recovered and used when needed, while free means that it's available now.
|
|
||||||
|
|
||||||
### When to worry
|
|
||||||
|
|
||||||
If performance on a Linux systems appears to be good — applications are responsive, the command line shows no indications of a problem — chances are the system's in good shape. Keep in mind that some application might be slowed down for some reason that doesn't affect the overall system.
|
|
||||||
|
|
||||||
An excessive number of hard faults may indeed indicate a problem, but balance this with observed performance.
|
|
||||||
|
|
||||||
A good rule of thumb is to worry when available memory is close to zero or when the "swap used" field grows or fluctuates noticeably. Don't worry if the "available" figure is a reasonable percentage of the total memory available as it is in the example from above repeated here:
|
|
||||||
|
|
||||||
```
|
|
||||||
$ free -m
|
|
||||||
total used free shared buff/cache available
|
|
||||||
Mem: 3244 3069 35 49 140 667
|
|
||||||
Swap: 3535 0 3535
|
|
||||||
```
|
|
||||||
|
|
||||||
### Linux performance is complicated
|
|
||||||
|
|
||||||
All that aside, memory on a Linux system can fill up and performance can slow down. Just don't take one report on memory usage as an indication that your system's in trouble.
|
|
||||||
|
|
||||||
Memory management on Linux systems is complicated because of the measures taken to ensure the best use of system resources. Don't let the initial appearance of full memory trick you into believing that your system is in trouble when it isn't.
|
|
||||||
|
|
||||||
**[ Two-Minute Linux Tips:[Learn how to master a host of Linux commands in these 2-minute video tutorials][3] ]**
|
|
||||||
|
|
||||||
Join the Network World communities on [Facebook][4] and [LinkedIn][5] to comment on topics that are top of mind.
|
|
||||||
|
|
||||||
--------------------------------------------------------------------------------
|
|
||||||
|
|
||||||
via: https://www.networkworld.com/article/3394603/when-to-be-concerned-about-memory-levels-on-linux.html
|
|
||||||
|
|
||||||
作者：[Sandra Henry-Stocker][a]
|
|
||||||
选题：[lujun9972][b]
|
|
||||||
译者：[译者ID](https://github.com/译者ID)
|
|
||||||
校对：[校对者ID](https://github.com/校对者ID)
|
|
||||||
|
|
||||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
|
||||||
|
|
||||||
[a]: https://www.networkworld.com/author/Sandra-Henry_Stocker/
|
|
||||||
[b]: https://github.com/lujun9972
|
|
||||||
[1]: https://images.idgesg.net/images/article/2019/05/full-swimming-pool-100796221-large.jpg
|
|
||||||
[2]: https://www.networkworld.com/article/3391029/must-know-linux-commands.html
|
|
||||||
[3]: https://www.youtube.com/playlist?list=PL7D2RMSmRO9J8OTpjFECi8DJiTQdd4hua
|
|
||||||
[4]: https://www.facebook.com/NetworkWorld/
|
|
||||||
[5]: https://www.linkedin.com/company/network-world
|
|
||||||
@ -0,0 +1,117 @@
|
|||||||
|
[#]: collector: (lujun9972)
|
||||||
|
[#]: translator: (luuming)
|
||||||
|
[#]: reviewer: ( )
|
||||||
|
[#]: publisher: ( )
|
||||||
|
[#]: url: ( )
|
||||||
|
[#]: subject: (When to be concerned about memory levels on Linux)
|
||||||
|
[#]: via: (https://www.networkworld.com/article/3394603/when-to-be-concerned-about-memory-levels-on-linux.html)
|
||||||
|
[#]: author: (Sandra Henry-Stocker https://www.networkworld.com/author/Sandra-Henry_Stocker/)
|
||||||
|
|
||||||
|
何时需要关注 linux 的内存层面？
|
||||||
|
======
|
||||||
|
Linux 上的内存管理很复杂。尽管使用率高但未必存在问题。你也应当关注一些其他的事情。
|
||||||
|
![Qfamily \(CC BY 2.0\)][1]
|
||||||
|
|
||||||
|
在 Linux 上用光内存通常并不意味着存在严重的问题。为什么？因为健康的 Linux 系统会在内存中缓存磁盘活动，基本上占用掉了未被使用的内存，这显然是一件好事情。
|
||||||
|
|
||||||
|
换句话说，它不让内存浪费掉。使用空闲的内存增加磁盘访问速度，并且不占用运行中应用程序的内存。你也能够想到，使用这种内存缓存比起直接访问硬盘驱动（HDD）快上数百倍，也比明显快于直接访问固态硬盘驱动。内存占满或几乎占满通常意味着系统正在尽可能高效地运行当中——并不是运行中遇到了问题。
|
||||||
|
|
||||||
|
### 缓存如何工作
|
||||||
|
|
||||||
|
磁盘缓存简单地意味着系统充分利用未使用的资源（空闲内存）来加速磁盘读取与写入。应用程序不会失去任何东西，并且大多数时间里能够按需求获得更多的内存。此外，磁盘缓存不会导致应用程序使用交换分区。反而，用作磁盘缓存的内存空间当被需要时会立即归还，并且磁盘内容会被更新。
|
||||||
|
|
||||||
|
### 主要和次要的页故障
|
||||||
|
|
||||||
|
Linux 系统通过分割物理内存为进程分配空间，将分割成的块称为“页”，并且映射这些页到每个进程的虚拟内存上。不再会用到的页也许会从内存中移除，尽管相关的进程还在运行。当进程需要一个没有被映射或没在内存中页时，故障便会产生。所以，“<ruby>故障<rt>fault</rt></ruby>”并不意味着“<ruby>错误<rt>error</rt></ruby>”而是“<ruby>不可用<rt>unavailables</rt></ruby>”，并且故障在内存管理中扮演者一个重要的角色。
|
||||||
|
|
||||||
|
次要故障意味着在内存中的页未分配给请求的进程或未在内存管理单元中标记为出现。主要故障意味着页不保留在内存中。
|
||||||
|
|
||||||
|
如果你想切身感受一下次要页故障和主要页故障出现的频率，像这样试一下 `ps` 命令。注意我们要的是与页故障和产生它的命令相关的项。输出中省略了很多行。`MINFL` 显示出次要故障的数目，而 `MAJFL` 表示了主要故障的数目。
|
||||||
|
|
||||||
|
```
|
||||||
|
$ ps -eo min_flt,maj_flt,cmd
|
||||||
|
MINFL MAJFL CMD
|
||||||
|
230760 150 /usr/lib/systemd/systemd --switched-root --system --deserialize 18
|
||||||
|
0 0 [kthreadd]
|
||||||
|
0 0 [rcu_gp]
|
||||||
|
0 0 [rcu_par_gp]
|
||||||
|
0 0 [kworker/0:0H-kblockd]
|
||||||
|
...
|
||||||
|
166 20 gpg-agent --homedir /var/lib/fwupd/gnupg --use-standard-socket --daemon
|
||||||
|
525 1 /usr/libexec/gvfsd-trash --spawner :1.16 /org/gtk/gvfs/exec_spaw/0
|
||||||
|
4966 4 /usr/libexec/gnome-terminal-server
|
||||||
|
3617 0 bash
|
||||||
|
0 0 [kworker/1:0H-kblockd]
|
||||||
|
927 0 gdm-session-worker [pam/gdm-password]
|
||||||
|
```
|
||||||
|
|
||||||
|
汇报单一进程，你可以尝试这样的命令：
|
||||||
|
|
||||||
|
```
|
||||||
|
$ ps -o min_flt,maj_flt 1
|
||||||
|
MINFL MAJFL
|
||||||
|
230064 150
|
||||||
|
```
|
||||||
|
|
||||||
|
你也可以添加其他的项，例如进程所有者的 UID 和 GID。
|
||||||
|
|
||||||
|
```
|
||||||
|
$ ps -o min_flt,maj_flt,cmd,args,uid,gid 1
|
||||||
|
MINFL MAJFL CMD COMMAND UID GID
|
||||||
|
230064 150 /usr/lib/systemd/systemd -- /usr/lib/systemd/systemd -- 0 0
|
||||||
|
```
|
||||||
|
|
||||||
|
### 多少才算满？
|
||||||
|
|
||||||
|
一种较好的方法来掌握内存究竟使用了多少是用 `free -m` 命令。`-m` 选项指定了数字的单位是 <ruby>MiBs<rt>mebibytes</rt></ruby> 而不是字节。
|
||||||
|
|
||||||
|
```
|
||||||
|
$ free -m
|
||||||
|
total used free shared buff/cache available
|
||||||
|
Mem: 3244 3069 35 49 140 667
|
||||||
|
Swap: 3535 0 3535
|
||||||
|
```
|
||||||
|
|
||||||
|
注意 `free`（未使用）的内存可能会不足，而 `available`（可用于启动新的应用）会显示更大的数量。这两者的区别值得我们去关注。<ruby>可用<rt>available</rt></ruby>意味着它可以在需要时恢复使用，而<ruby>空闲<rt>free</rt></ruby>意味着现在就能够使用。
|
||||||
|
|
||||||
|
### 什么时候要担心
|
||||||
|
|
||||||
|
如果 Linux 系统上的性能表现良好——应用程序响应度高，命令行没有显示出问题——很可能系统状况良好。记住，一些应用也许会出于某种原因而变慢，但它不影响整个系统。
|
||||||
|
|
||||||
|
过多的硬故障也许表明确实存在问题，但要将其与观察到的性能相比较。
|
||||||
|
|
||||||
|
一个好的方法是当可用内存接近 0 或者“<ruby>用作交换<rt>swap used</rt></ruby>”项显著增长或波动时开始担心。如果“可用”项占总内存可用量的百分比合理，那么就无需担心，就像下面的例子那样：
|
||||||
|
|
||||||
|
```
|
||||||
|
$ free -m
|
||||||
|
total used free shared buff/cache available
|
||||||
|
Mem: 3244 3069 35 49 140 667
|
||||||
|
Swap: 3535 0 3535
|
||||||
|
```
|
||||||
|
|
||||||
|
### Linux 性能很复杂
|
||||||
|
|
||||||
|
把所有的放在一边，Linux 系统上的内存可能会变满，并且性能可能会降低。当系统出现问题时不要仅将单一的内存使用报告作为指标。
|
||||||
|
|
||||||
|
Linux 系统的内存管理很复杂，因为它采取的措施需要确保系统资源得到最好的利用。不要受到一开始内存占满的欺骗，使你认为系统存在问题，但实际上并没有。
|
||||||
|
|
||||||
|
在 [Facebook][4] 和 [LinkedIn][5] 上加入网络研讨会发表你的评论。
|
||||||
|
|
||||||
|
--------------------------------------------------------------------------------
|
||||||
|
|
||||||
|
via: https://www.networkworld.com/article/3394603/when-to-be-concerned-about-memory-levels-on-linux.html
|
||||||
|
|
||||||
|
作者：[Sandra Henry-Stocker][a]
|
||||||
|
选题：[lujun9972][b]
|
||||||
|
译者：[LuuMing](https://github.com/LuuMing)
|
||||||
|
校对：[校对者ID](https://github.com/校对者ID)
|
||||||
|
|
||||||
|
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||||
|
|
||||||
|
[a]: https://www.networkworld.com/author/Sandra-Henry_Stocker/
|
||||||
|
[b]: https://github.com/lujun9972
|
||||||
|
[1]: https://images.idgesg.net/images/article/2019/05/full-swimming-pool-100796221-large.jpg
|
||||||
|
[2]: https://www.networkworld.com/article/3391029/must-know-linux-commands.html
|
||||||
|
[3]: https://www.youtube.com/playlist?list=PL7D2RMSmRO9J8OTpjFECi8DJiTQdd4hua
|
||||||
|
[4]: https://www.facebook.com/NetworkWorld/
|
||||||
|
[5]: https://www.linkedin.com/company/network-world
|
||||||
Loading…
Reference in New Issue
Block a user