寫點東西吧，懒人。

Kernel - Page Frame 回收
· ☕ 4 分钟

From [Understanding The Linux Kernel]

Page Frame 回收

之前我们了解到，Linux 倾向用最多的内存做 Page Cache。这使我们不得不考虑如何在内存不足前回收内存。问题是，回收内存的程序本身也可能有 IO 操作，也可能需要内存。

Kernel - Pagecache
· ☕ 1 分钟

简介

page cache 存放的数据的类型

  • 普通的文件
  • 目录数据
  • 直接读取自 block device file 的数据
  • 已经被swap out的用户进程内存的数据（可以强制内核在page cahce中保留一些已经被swap out的数据）
  • 归属于一些特殊 filesystem 的内存 page，如用于进程间通讯的 shm filesystem

page cache 的标识体系

page cache 中的每个 page 均归属于文件. 这个文件 — 或更精确来说，是文件的 inode 被称为 page 的owner.

Kernel - Pagecache - Core
· ☕ 3 分钟

address_space 数据结构

Page cahce 的核心数据结构是 addrees_space。一般来说，每个 inode （Kernel 用来存放文件元信息的内存中的数据结构，可以视为一个文件的描述信息）中包含一个 addrees_space 。

· ☕ 4 分钟

https://tenzir.com/blog/production-debugging-bpftrace-uprobes/
https://shaharmike.com/cpp/vtable-part1/

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#include <iostream>

class Parent {
 public:
  virtual void Foo() {}
  virtual void FooNotOverridden() {}
};

class Derived : public Parent {
 public:
  void Foo() override {}
};

int main() {
  Parent p1, p2;
  Derived d1, d2;

  std::cout << "done" << std::endl;
}

$ # compile our code with debug symbols and start debugging using gdb
$ clang++ -std=c++14 -stdlib=libc++ -g main.cpp && gdb ./a.out
...
(gdb) # ask gdb to automatically demangle C++ symbols
(gdb) set print asm-demangle on
(gdb) set print demangle on
(gdb) # set breakpoint at main
(gdb) b main
Breakpoint 1 at 0x4009ac: file main.cpp, line 15.
(gdb) run
Starting program: /home/shmike/cpp/a.out

Breakpoint 1, main () at main.cpp:15
15	  Parent p1, p2;
(gdb) # skip to next line
(gdb) n
16	  Derived d1, d2;
(gdb) # skip to next line
(gdb) n
18	  std::cout << "done" << std::endl;
(gdb) # print p1, p2, d1, d2 - we'll talk about what the output means soon
(gdb) p p1
$1 = {_vptr$Parent = 0x400bb8 <vtable for Parent+16>}
(gdb) p p2
$2 = {_vptr$Parent = 0x400bb8 <vtable for Parent+16>}
(gdb) p d1
$3 = {<Parent> = {_vptr$Parent = 0x400b50 <vtable for Derived+16>}, <No data fields>}
(gdb) p d2
$4 = {<Parent> = {_vptr$Parent = 0x400b50 <vtable for Derived+16>}, <No data fields>}

Here’s what we learned from the above:

· ☕ 3 分钟

Terminology

  • Cluster: a logical service with a set of endpoints that Envoy forwards requests to.

  • Downstream: an entity connecting to Envoy. This may be a local application (in a sidecar model) or a network node. In non-sidecar models, this is a remote client.

  • Endpoints: network nodes that implement a logical service. They are grouped into clusters. Endpoints in a cluster are upstream of an Envoy proxy.

  • Filter: a module in the connection or request processing pipeline providing some aspect of request handling. An analogy from Unix is the composition of small utilities (filters) with Unix pipes (filter chains).

· ☕ 0 分钟
· ☕ 1 分钟

https://istio.cn/t/topic/299

Envoy源码分析之Dispatcher：https://developer.aliyun.com/article/659277

线程相关 Misc：

  • Envoy进程由一个Main Thread和多个Worker Thread 组成
  • 每个Main和Worker包含一个eventloop，所有的处理都是由eventloop触发开始
  • Main负责xDS等功能，Worker负责处理连接和请求
  • 当一个client向Envoy建立连接的时候，因为所有Worker的EventLoop都注册了listening fd(启用SO_PORTREUSE除外)，会由内核决定分配给哪个Worker
  • 当一个下游client连接到了Envoy，在保持连接不断的情况下，会和同一个Worker进行通讯
· ☕ 2 分钟

HTTP/1.1 Header Casing

https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_conn_man/header_casing#config-http-conn-man-header-casing

When handling HTTP/1.1, Envoy will normalize the header keys to be all lowercase. While this is compliant with the HTTP/1.1 spec, in practice this can result in issues when migrating existing systems that might rely on specific header casing.

To support these use cases, Envoy allows configuring a formatting scheme for the headers, which will have Envoy transform the header keys during serialization.

  • To configure this formatting on response headers, specify the format in the http_protocol_options.
  • To configure this for upstream request headers, specify the formatting in http_protocol_options in the cluster’s extension_protocol_options.

Currently Envoy supports two mutually exclusive types of header key formatters: