46 lines
3.0 KiB
Markdown
46 lines
3.0 KiB
Markdown
# Linux Page Cache for SRE
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- **期号**: SRE Weekly Issue #289（2021-09-26）
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- **作者**: Viacheslav Biriukov
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- **链接**: https://biriukov.dev/docs/page-cache/0-linux-page-cache-for-sre/
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## 简介
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An in-depth explainer on the Linux page cache, full of details and experiments.
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## 正文
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#
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SRE deep dive into Linux Page Cache
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[#](https://biriukov.dev#sre-deep-dive-into-linux-page-cache)
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**Contents**
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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:
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- more **precise capacity planning** and**container limit calculations** ;
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- better **debugging and investigation skills** for memory and disk intensive applications such as**database management system** and file sharing**storages** ;
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- building **safe and predictable runtimes** for memory and/or IO-bound ad-hoc tasks (for instance: backups and restore scripts,`rsync` one-liners, etc.).
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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`.
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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:
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- `procfs` files:`/proc/PID/smaps` ,`/proc/pid/pagemap` ,`/proc/kpageflags` ,`/proc/kpagecgroup` and`sysfs` file:`/sys/kernel/mm/page_idle` ;
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- system calls: `mincore()` ,`mmap()` ,`fsync()` ,`msync()` ,`posix_fadvise()` ,`madvise()` and others;
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- different open and advise flags `O_SYNC` ,`FADV_DONTNEED` ,`POSIX_FADV_RANDOM` ,`MADV_DONTNEED` , etc.
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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.
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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.
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Readers should be confident if they have middle GNU/Linux knowledge and basic programming skills.
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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).
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[Read next chapter →](https://biriukov.dev/docs/page-cache/1-prepare-environment-for-experiments/)
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