# Linux Page Cache for SRE

- **期号**: SRE Weekly Issue #289（2021-09-26）
- **作者**: Viacheslav Biriukov
- **链接**: https://biriukov.dev/docs/page-cache/0-linux-page-cache-for-sre/

## 简介

An in-depth explainer on the Linux page cache, full of details and experiments.

## 正文

# 
  SRE deep dive into Linux Page Cache
  [#](https://biriukov.dev#sre-deep-dive-into-linux-page-cache)

    
        
    

**Contents**

In this series of articles, I would like to talk about **Linux Page Cache**. I believe that the following knowledge of the theory and tools is **essential and crucial for every SRE**. This understanding can help both in usual and routine everyday DevOps-like tasks and in emergency debugging and firefighting. Page Cache is often left unattended, and its better understanding leads to the following:

- more **precise capacity planning** and**container limit calculations** ;
- better **debugging and investigation skills** for memory and disk intensive applications such as**database management system** and file sharing**storages** ;
- building **safe and predictable runtimes** for memory and/or IO-bound ad-hoc tasks (for instance: backups and restore scripts,`rsync` one-liners, etc.).

I’ll display what **utils** you should keep in mind when you’re dealing with Page Cache related tasks and problems, how to use them properly **to understand real memory usage**, and how to **reveal issues** with them. I will try to give you some examples of using these tools that are close to real life situations. Here are some of these tools I’m talking about below: `vmtouch`, `perf`, `cgtouch`, `strace` , `sar` and `page-type`.

Also, as the title says, “deep dive”,  **the internals of these utils** will be shown with an emphasis on the **Page Cache** stats, events, syscalls and kernel interfaces. Here are some examples of what I’m touching on in the following post:

- `procfs` files:`/proc/PID/smaps` ,`/proc/pid/pagemap` ,`/proc/kpageflags` ,`/proc/kpagecgroup` and`sysfs` file:`/sys/kernel/mm/page_idle` ;
- system calls: `mincore()` ,`mmap()` ,`fsync()` ,`msync()` ,`posix_fadvise()` ,`madvise()` and others;
- different open and advise flags `O_SYNC` ,`FADV_DONTNEED` ,`POSIX_FADV_RANDOM` ,`MADV_DONTNEED` , etc.

I’ll try to be as verbose as possible with simple (almost all the way) code examples in Python, Go and a tiny bit of C.

And finally, any conversations about modern GNU/Linux systems can’t be fully conducted without touching the **`cgroup`** (`v2` in our case) and the **`systemd`** topics. I’ll show you **how to leverage them** to get the most out of the systems, build reliable, well-observed, controlled services, and sleep well at night while on-call.

Readers should be confident if they have middle GNU/Linux knowledge and basic programming skills.

All code examples larger than 5 lines can be found on github: [https://github.com/brk0v/sre-page-cache-article](https://github.com/brk0v/sre-page-cache-article).

[Read next chapter →](https://biriukov.dev/docs/page-cache/1-prepare-environment-for-experiments/)