Update ebpf doc (#12503)

1 files changed, 556 insertions, 520 deletions

diff --git a/collectors/ebpf.plugin/README.md b/collectors/ebpf.plugin/README.md
index 0f943416c6..c32133b1c7 100644
--- a/collectors/ebpf.plugin/README.md
+++ b/collectors/ebpf.plugin/README.md
@@ -8,51 +8,405 @@ sidebar_label: "eBPF"
 
 # eBPF monitoring with Netdata
 
-eBPF consists of a wide toolchain that ultimately outputs a set of bytecode that will run inside the eBPF virtual
-machine (VM) which lives inside the Linux kernel. The program in particular is executed in response to a [tracepoint
-or kprobe](#probes-and-tracepoints) activation.
+The Netdata Agent provides many [eBPF](https://ebpf.io/what-is-ebpf/) programs to help you troubleshoot and debug how applications interact with the Linux kernel. The `ebpf.plugin` uses [tracepoints, trampoline, and2 kprobes](#data-collection) to collect a wide array of high value data about the host that would otherwise be impossible to capture. 
 
-Netdata has written many eBPF programs, which, when compiled and integrated into the Netdata Agent, are able to collect
-a wide array of data about the host that would otherwise be impossible. The data eBPF programs can collect is truly unique,
-which gives the Netdata Agent access to data that is high value but normally hard to capture.
+> ❗ eBPF monitoring only works on Linux systems and with specific Linux kernels, including all kernels newer than `4.11.0`, and all kernels on CentOS 7.6 or later. For kernels older than `4.11.0`, improved support is in active development.
 
-eBPF monitoring can help you troubleshoot and debug how applications interact with the Linux kernel. See
-our [guide on troubleshooting apps with eBPF metrics](/docs/guides/troubleshoot/monitor-debug-applications-ebpf.md) for
-configuration and troubleshooting tips.
+This document provides comprehensive details about the `ebpf.plugin`.
+For hands-on configuration and troubleshooting tips see our [tutorial on troubleshooting apps with eBPF metrics](/docs/guides/troubleshoot/monitor-debug-applications-ebpf.md).
 
 <figure>
   <img src="https://user-images.githubusercontent.com/1153921/74746434-ad6a1e00-5222-11ea-858a-a7882617ae02.png" alt="An example of VFS charts, made possible by the eBPF collector plugin" />
-  <figcaption>An example of VFS charts made possible by the eBPF collector plugin.</figcaption>
+  <figcaption>An example of virtual file system (VFS) charts made possible by the eBPF collector plugin.</figcaption>
 </figure>
 
-## Probes and Tracepoints
+<a id="data-collection"> </a>
 
-The following two features from the Linux kernel are used by Netdata to run eBPF programs:
+## How Netdata collects data using probes and tracepoints
 
-- Kprobes and return probes (kretprobe): Probes can insert virtually into any kernel instruction. When eBPF runs in
-  `entry` mode, it attaches only `kprobes` for internal functions monitoring calls and some arguments every time a
-  function is called. The user can also change configuration to use [`return`](#global) mode, and this will allow users
-  to monitor return from these functions and detect possible failures.
-- Tracepoints are hooks to call specific functions. Tracepoints are more stable than `kprobes` and are preferred when
-  both options are available.
+Netdata uses the following features from the Linux kernel to run eBPF programs:
 
-In each case, wherever a normal kprobe, kretprobe, or tracepoint would have run its hook function, an eBPF program is
-run instead, performing various collection logic before letting the kernel continue its normal control flow.
+-   Tracepoints are hooks to call specific functions. Tracepoints are more stable than `kprobes` and are preferred when
+    both options are available.
+-   Trampolines are bridges between kernel functions, and BPF programs. Netdata uses them by default whenever available.
+-   Kprobes and return probes (`kretprobe`): Probes can insert virtually into any kernel instruction. When eBPF runs in `entry` mode, it attaches only `kprobes` for internal functions monitoring calls and some arguments every time a function is called. The user can also change configuration to use [`return`](#global) mode, and this will allow users to monitor return from these functions and detect possible failures.
 
-There are more methods by which eBPF programs can be triggered but which are not currently supported, such as via uprobes
-which allow hooking into arbitrary user-space functions in a similar manner to kprobes.
+In each case, wherever a normal kprobe, kretprobe, or tracepoint would have run its hook function, an eBPF program is run instead, performing various collection logic before letting the kernel continue its normal control flow.
 
-## Manually enable the collector on Linux
+There are more methods to trigger eBPF programs, such as uprobes, but currently are not supported.
 
-**The eBPF collector is installed and enabled by default on most new installations of the Agent**. The eBPF collector
-does not currently work with [static build installations](/packaging/installer/methods/kickstart.md#static-builds) for kernels older
-than `4.11`, but improved support is in active development.
+## Configuring ebpf.plugin
 
-eBPF monitoring only works on Linux systems and with specific Linux kernels, including all kernels newer than `4.11.0`,
-and all kernels on CentOS 7.6 or later.
+The eBPF collector is installed and enabled by default on most new installations of the Agent.
+If your Agent is v1.22 or older, you may to enable the collector yourself. 
 
-If your Agent is v1.22 or older, you may to enable the collector yourself. See the [configuration](#configuration)
-section for details.
+### Enable the eBPF collector
+
+To enable or disable the entire eBPF collector: 
+
+1.  Navigate to the [Netdata config directory](/docs/configure/nodes.md#the-netdata-config-directory).
+    ```bash
+    cd /etc/netdata
+    ```
+
+2.  Use the [`edit-config`](/docs/configure/nodes.md#use-edit-config-to-edit-configuration-files) script to edit `netdata.conf`.
+
+    ```bash
+    ./edit-config netdata.conf
+    ```
+
+3.  Enable the collector by scrolling down to the `[plugins]` section. Uncomment the line `ebpf` (not
+    `ebpf_process`) and set it to `yes`.
+
+    ```conf
+    [plugins]
+       ebpf = yes
+    ```
+
+### Configure the eBPF collector
+
+You can configure the eBPF collector's behavior to fine-tune which metrics you receive and [optimize performance]\(#performance opimization).
+
+To edit the `ebpf.d.conf`:
+
+1.  Navigate to the [Netdata config directory](/docs/configure/nodes.md#the-netdata-config-directory).
+    ```bash
+    cd /etc/netdata
+    ```
+2.  Use the [`edit-config`](/docs/configure/nodes.md#use-edit-config-to-edit-configuration-files) script to edit [`ebpf.d.conf`](https://github.com/netdata/netdata/blob/master/collectors/ebpf.plugin/ebpf.d.conf).
+
+    ```bash
+    ./edit-config ebpf.d.conf
+    ```
+
+    You can now edit the behavior of the eBPF collector. The following sections describe each configuration option in detail.
+
+### `[global]` configuration options
+
+The `[global]` section defines settings for the whole eBPF collector.
+
+#### eBPF load mode
+
+The collector uses two different eBPF programs. These programs rely on the same functions inside the kernel, but they
+monitor, process, and display different kinds of information.
+
+By default, this plugin uses the `entry` mode. Changing this mode can create significant overhead on your operating
+system, but also offer valuable information if you are developing or debugging software. The `ebpf load mode` option
+accepts the following values:
+
+-   `entry`: This is the default mode. In this mode, the eBPF collector only monitors calls for the functions described in
+    the sections above, and does not show charts related to errors.
+-   `return`: In the `return` mode, the eBPF collector monitors the same kernel functions as `entry`, but also creates new
+    charts for the return of these functions, such as errors. Monitoring function returns can help in debugging software,
+    such as failing to close file descriptors or creating zombie processes.
+-   `update every`:  Number of seconds used for eBPF to send data for Netdata.
+-   `pid table size`: Defines the maximum number of PIDs stored inside the application hash table.
+
+#### Integration with `apps.plugin`
+
+The eBPF collector also creates charts for each running application through an integration with the
+[`apps.plugin`](/collectors/apps.plugin/README.md). This integration helps you understand how specific applications
+interact with the Linux kernel.
+
+If you want to _disable_ the integration with `apps.plugin` along with the above charts, change the setting `apps` to
+`no`.
+
+```conf
+[global]
+   apps = yes
+```
+
+When the integration is enabled, eBPF collector allocates memory for each process running. The total allocated memory
+has direct relationship with the kernel version. When the eBPF plugin is running on kernels newer than `4.15`, it uses
+per-cpu maps to speed up the update of hash tables. This also implies storing data for the same PID for each processor
+it runs.
+
+#### Integration with `cgroups.plugin`
+
+The eBPF collector also creates charts for each cgroup through an integration with the
+[`cgroups.plugin`](/collectors/cgroups.plugin/README.md). This integration helps you understand how a specific cgroup
+interacts with the Linux kernel.
+
+The integration with `cgroups.plugin` is disabled by default to avoid creating overhead on your system. If you want to
+_enable_ the integration with `cgroups.plugin`, change the `cgroups` setting to `yes`.
+
+```conf
+[global]
+   cgroups = yes
+```
+
+If you do not need to monitor specific metrics for your `cgroups`, you can enable `cgroups` inside
+`ebpf.d.conf`, and then disable the plugin for a specific `thread` by following the steps in the
+[Configuration](#configuration) section.
+
+#### Integration Dashboard Elements
+
+When an integration is enabled, your dashboard will also show the following cgroups and apps charts using low-level
+Linux metrics:
+
+> Note: The parenthetical accompanying each bulleted item provides the chart name.
+
+-   mem
+    -   Number of processes killed due out of memory. (`oomkills`)
+-   process
+    -   Number of processes created with `do_fork`. (`process_create`)
+    -   Number of threads created with `do_fork` or `clone (2)`, depending on your system's kernel
+        version. (`thread_create`)
+    -   Number of times that a process called `do_exit`. (`task_exit`)
+    -   Number of times that a process called `release_task`. (`task_close`)
+    -   Number of times that an error happened to create thread or process. (`task_error`)
+-   swap
+    -   Number of calls to `swap_readpage`. (`swap_read_call`)
+    -   Number of calls to `swap_writepage`. (`swap_write_call`)
+-   network
+    -   Number of outbound connections using TCP/IPv4. (`outbound_conn_ipv4`)
+    -   Number of outbound connections using TCP/IPv6. (`outbound_conn_ipv6`)
+    -   Number of bytes sent. (`total_bandwidth_sent`)
+    -   Number of bytes received. (`total_bandwidth_recv`)
+    -   Number of calls to `tcp_sendmsg`. (`bandwidth_tcp_send`)
+    -   Number of calls to `tcp_cleanup_rbuf`. (`bandwidth_tcp_recv`)
+    -   Number of calls to `tcp_retransmit_skb`. (`bandwidth_tcp_retransmit`)
+    -   Number of calls to `udp_sendmsg`. (`bandwidth_udp_send`)
+    -   Number of calls to `udp_recvmsg`. (`bandwidth_udp_recv`)
+-   file access
+    -   Number of calls to open files. (`file_open`)
+    -   Number of calls to open files that returned errors. (`open_error`)
+    -   Number of files closed. (`file_closed`)
+    -   Number of calls to close files that returned errors. (`file_error_closed`)
+-   vfs
+    -   Number of calls to `vfs_unlink`. (`file_deleted`)
+    -   Number of calls to `vfs_write`. (`vfs_write_call`)
+    -   Number of calls to write a file that returned errors. (`vfs_write_error`)
+    -   Number of calls to `vfs_read`. (`vfs_read_call`)
+    -   -   Number of calls to read a file that returned errors. (`vfs_read_error`)
+    -   Number of bytes written with `vfs_write`. (`vfs_write_bytes`)
+    -   Number of bytes read with `vfs_read`. (`vfs_read_bytes`)
+    -   Number of calls to `vfs_fsync`. (`vfs_fsync`)
+    -   Number of calls to sync file that returned errors. (`vfs_fsync_error`)
+    -   Number of calls to `vfs_open`. (`vfs_open`)
+    -   Number of calls to open file that returned errors. (`vfs_open_error`)
+    -   Number of calls to `vfs_create`. (`vfs_create`)
+    -   Number of calls to open file that returned errors. (`vfs_create_error`)
+-   page cache
+    -   Ratio of pages accessed. (`cachestat_ratio`)
+    -   Number of modified pages ("dirty"). (`cachestat_dirties`)
+    -   Number of accessed pages. (`cachestat_hits`)
+    -   Number of pages brought from disk. (`cachestat_misses`)
+-   directory cache
+    -   Ratio of files available in directory cache. (`dc_hit_ratio`)
+    -   Number of files accessed. (`dc_reference`)
+    -   Number of files accessed that were not in cache. (`dc_not_cache`)
+    -   Number of files not found. (`dc_not_found`)
+-   ipc shm
+    -   Number of calls to `shm_get`. (`shmget_call`)
+    -   Number of calls to `shm_at`. (`shmat_call`)
+    -   Number of calls to `shm_dt`. (`shmdt_call`)
+    -   Number of calls to `shm_ctl`. (`shmctl_call`)
+
+### `[ebpf programs]` configuration options
+
+The eBPF collector enables and runs the following eBPF programs by default:
+
+-   `fd` :  This eBPF program creates charts that show information about calls to open files.
+-   `mount`: This eBPF program creates charts that show calls to syscalls mount(2) and umount(2).
+-   `shm`: This eBPF program creates charts that show calls to syscalls shmget(2), shmat(2), shmdt(2) and shmctl(2).
+-   `sync`: Monitor calls to syscalls sync(2), fsync(2), fdatasync(2), syncfs(2), msync(2), and sync_file_range(2).
+-   `network viewer`: This eBPF program creates charts with information about `TCP` and `UDP` functions, including the
+    bandwidth consumed by each.
+-   `vfs`: This eBPF program creates charts that show information about VFS (Virtual File System) functions.
+-   `process`: This eBPF program creates charts that show information about process life. When in `return` mode, it also
+    creates charts showing errors when these operations are executed.
+-   `hardirq`: This eBPF program creates charts that show information about time spent servicing individual hardware
+    interrupt requests (hard IRQs).
+-   `softirq`: This eBPF program creates charts that show information about time spent servicing individual software
+    interrupt requests (soft IRQs).
+-   `oomkill`: This eBPF program creates a chart that shows OOM kills for all applications recognized via
+    the `apps.plugin` integration. Note that this program will show application charts regardless of whether apps
+    integration is turned on or off.
+
+You can also enable the following eBPF programs:
+
+-   `cachestat`: Netdata's eBPF data collector creates charts about the memory page cache. When the integration with
+    [`apps.plugin`](/collectors/apps.plugin/README.md) is enabled, this collector creates charts for the whole host _and_
+    for each application.
+-   `dcstat` : This eBPF program creates charts that show information about file access using directory cache. It appends
+    `kprobes` for `lookup_fast()` and `d_lookup()` to identify if files are inside directory cache, outside and files are
+    not found.
+-   `disk` : This eBPF program creates charts that show information about disk latency independent of filesystem.
+-   `filesystem` : This eBPF program creates charts that show information about some filesystem latency.
+-   `swap` : This eBPF program creates charts that show information about swap access.
+-   `mdflush`: This eBPF program creates charts that show information about
+    multi-device software flushes.
+
+### Configuring eBPF threads
+
+You can configure each thread of the eBPF data collector. This allows you to overwrite global options defined in `/etc/netdata/ebpf.d.conf` and configure specific options for each thread.
+
+To configure an eBPF thread:
+
+1.  Navigate to the [Netdata config directory](/docs/configure/nodes.md#the-netdata-config-directory).
+    ```bash
+    cd /etc/netdata
+    ```
+2.  Use the [`edit-config`](/docs/configure/nodes.md#use-edit-config-to-edit-configuration-files) script to edit a thread configuration file. The following configuration files are available:
+
+    -   `network.conf`: Configuration for the [`network` thread](#network-configuration). This config file overwrites the global options and also
+        lets you specify which network the eBPF collector monitors.
+    -   `process.conf`: Configuration for the [`process` thread](#sync-configuration).
+    -   `cachestat.conf`: Configuration for the `cachestat` thread(#filesystem-configuration).
+    -   `dcstat.conf`: Configuration for the `dcstat` thread.
+    -   `disk.conf`: Configuration for the `disk` thread.
+    -   `fd.conf`: Configuration for the `file descriptor` thread.
+    -   `filesystem.conf`: Configuration for the `filesystem` thread.
+    -   `hardirq.conf`: Configuration for the `hardirq` thread.
+    -   `softirq.conf`: Configuration for the `softirq` thread.
+    -   `sync.conf`: Configuration for the `sync` thread.
+    -   `vfs.conf`: Configuration for the `vfs` thread.
+
+        ```bash
+        ./edit-config FILE.conf
+        ```
+
+### Network configuration
+
+The network configuration has specific options to configure which network(s) the eBPF collector monitors. These options
+are divided in the following sections:
+
+#### `[network connections]`
+
+You can configure the information shown on `outbound` and `inbound` charts with the settings in this section.
+
+```conf
+[network connections]
+    maximum dimensions = 500
+    resolve hostname ips = no
+    ports = 1-1024 !145 !domain
+    hostnames = !example.com
+    ips = !127.0.0.1/8 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 fc00::/7
+```
+
+When you define a `ports` setting, Netdata will collect network metrics for that specific port. For example, if you
+write `ports = 19999`, Netdata will collect only connections for itself. The `hostnames` setting accepts
+[simple patterns](/libnetdata/simple_pattern/README.md). The `ports`, and `ips` settings accept negation (`!`) to deny
+specific values or asterisk alone to define all values.
+
+In the above example, Netdata will collect metrics for all ports between 1 and 443, with the exception of 53 (domain)
+and 145.
+
+The following options are available:
+
+-   `ports`: Define the destination ports for Netdata to monitor.
+-   `hostnames`: The list of hostnames that can be resolved to an IP address.
+-   `ips`: The IP or range of IPs that you want to monitor. You can use IPv4 or IPv6 addresses, use dashes to define a
+    range of IPs, or use CIDR values. By default, only data for private IP addresses is collected, but this can
+    be changed with the `ips` setting.
+
+By default, Netdata displays up to 500 dimensions on network connection charts. If there are more possible dimensions,
+they will be bundled into the `other` dimension. You can increase the number of shown dimensions by changing
+the `maximum dimensions` setting.
+
+The dimensions for the traffic charts are created using the destination IPs of the sockets by default. This can be
+changed setting `resolve hostname ips = yes` and restarting Netdata, after this Netdata will create dimensions using
+the `hostnames` every time that is possible to resolve IPs to their hostnames.
+
+#### `[service name]`
+
+Netdata uses the list of services in `/etc/services` to plot network connection charts. If this file does not contain
+the name for a particular service you use in your infrastructure, you will need to add it to the `[service name]`
+section.
+
+For example, Netdata's default port (`19999`) is not listed in `/etc/services`. To associate that port with the Netdata
+service in network connection charts, and thus see the name of the service instead of its port, define it:
+
+```conf
+[service name]
+    19999 = Netdata
+```
+
+### Sync configuration
+
+The sync configuration has specific options to disable monitoring for syscalls.  All syscalls are monitored by default.
+
+```conf
+[syscalls]
+    sync = yes
+    msync = yes
+    fsync = yes
+    fdatasync = yes
+    syncfs = yes
+    sync_file_range = yes
+```
+
+### Filesystem configuration
+
+The filesystem configuration has specific options to disable monitoring for filesystems; by default, all filesystems are
+monitored.
+
+```conf
+[filesystem]
+    btrfsdist = yes
+    ext4dist = yes
+    nfsdist = yes
+    xfsdist = yes
+    zfsdist = yes
+```
+
+The ebpf program `nfsdist` monitors only `nfs` mount points.
+
+## Troubleshooting
+
+If the eBPF collector does not work, you can troubleshoot it by running the `ebpf.plugin` command and investigating its
+output.
+
+```bash
+cd /usr/libexec/netdata/plugins.d/
+sudo su -s /bin/bash ./ebpf.plugin
+```
+
+You can also use `grep` to search the Agent's `error.log` for messages related to eBPF monitoring.
+
+```bash
+grep -i ebpf /var/log/netdata/error.log
+```
+
+### Confirm kernel compatibility
+
+The eBPF collector only works on Linux systems and with specific Linux kernels. We support all kernels more recent than
+`4.11.0`, and all kernels on CentOS 7.6 or later.
+
+You can run our helper script to determine whether your system can support eBPF monitoring. If it returns no output, your system is ready to compile and run the eBPF collector.
+
+```bash
+curl -sSL https://raw.githubusercontent.com/netdata/kernel-collector/master/tools/check-kernel-config.sh | sudo bash
+```
+
+
+If you see a warning about a missing kernel
+configuration (`KPROBES KPROBES_ON_FTRACE HAVE_KPROBES BPF BPF_SYSCALL BPF_JIT`), you will need to recompile your kernel
+to support this configuration. The process of recompiling Linux kernels varies based on your distribution and version.
+Read the documentation for your system's distribution to learn more about the specific workflow for recompiling the
+kernel, ensuring that you set all the necessary
+
+-   [Ubuntu](https://wiki.ubuntu.com/Kernel/BuildYourOwnKernel)
+-   [Debian](https://kernel-team.pages.debian.net/kernel-handbook/ch-common-tasks.html#s-common-official)
+-   [Fedora](https://fedoraproject.org/wiki/Building_a_custom_kernel)
+-   [CentOS](https://wiki.centos.org/HowTos/Custom_Kernel)
+-   [Arch Linux](https://wiki.archlinux.org/index.php/Kernel/Traditional_compilation)
+-   [Slackware](https://docs.slackware.com/howtos:slackware_admin:kernelbuilding)
+
+### Mount `debugfs` and `tracefs`
+
+The eBPF collector also requires both the `tracefs` and `debugfs` filesystems. Try mounting the `tracefs` and `debugfs`
+filesystems using the commands below:
+
+```bash
+sudo mount -t debugfs nodev /sys/kernel/debug
+sudo mount -t tracefs nodev /sys/kernel/tracing
+```
+
+If they are already mounted, you will see an error. You can also configure your system's `/etc/fstab` configuration to
+mount these filesystems on startup. More information can be found in
+the [ftrace documentation](https://www.kernel.org/doc/Documentation/trace/ftrace.txt).
 
 ## Charts
 
@@ -64,8 +418,7 @@ collected in the previous and current seconds.
 
 ### System overview
 
-Not all charts within the System Overview menu are enabled by default, because they add around 100ns overhead for each
-function call, this number is small for a human perspective, but the functions are called many times creating an impact
+Not all charts within the System Overview menu are enabled by default. Charts that rely on `kprobes` are disabled by default because they add around 100ns overhead for each function call. This is a small number from a human's perspective, but the functions are called many times and create an impact
 on host. See the [configuration](#configuration) section for details about how to enable them.
 
 #### Processes
@@ -74,12 +427,12 @@ Internally, the Linux kernel treats both processes and threads as `tasks`. To cr
 system calls: `fork(2)`, `vfork(2)`, and `clone(2)`. To generate this chart, the eBPF
 collector uses the following `tracepoints` and `kprobe`:
 
-- `sched/sched_process_fork`: Tracepoint called after a call for `fork (2)`, `vfork (2)` and `clone (2)`.
-- `sched/sched_process_exec`: Tracepoint called after a exec-family syscall.
-- `kprobe/kernel_clone`: This is the main [`fork()`](https://elixir.bootlin.com/linux/v5.10/source/kernel/fork.c#L2415)
-   routine since kernel `5.10.0` was released.
-- `kprobe/_do_fork`: Like `kernel_clone`, but this was the main function between kernels `4.2.0` and `5.9.16`
-- `kprobe/do_fork`: This was the main function before kernel `4.2.0`.
+-   `sched/sched_process_fork`: Tracepoint called after a call for `fork (2)`, `vfork (2)` and `clone (2)`.
+-   `sched/sched_process_exec`: Tracepoint called after a exec-family syscall.
+-   `kprobe/kernel_clone`: This is the main [`fork()`](https://elixir.bootlin.com/linux/v5.10/source/kernel/fork.c#L2415)
+     routine since kernel `5.10.0` was released.
+-   `kprobe/_do_fork`: Like `kernel_clone`, but this was the main function between kernels `4.2.0` and `5.9.16`
+-   `kprobe/do_fork`: This was the main function before kernel `4.2.0`.
 
 #### Process Exit
 
@@ -88,9 +441,9 @@ system that the task is finishing its work. The second step is to release the ke
 function `release_task`. The difference between the two dimensions can help you discover
 [zombie processes](https://en.wikipedia.org/wiki/Zombie_process). To get the metrics, the collector uses:
 
-- `sched/sched_process_exit`: Tracepoint called after a task exits.
-- `kprobe/release_task`: This function is called when a process exits, as the kernel still needs to remove the process
-  descriptor.
+-   `sched/sched_process_exit`: Tracepoint called after a task exits.
+-   `kprobe/release_task`: This function is called when a process exits, as the kernel still needs to remove the process
+    descriptor.
 
 #### Task error
 
@@ -100,7 +453,7 @@ process and thread creation only.
 #### Swap
 
 Inside the swap submenu the eBPF plugin creates the chart `swapcalls`; this chart is displaying when processes are
-calling functions [`swap_readpage` and `swap_writepage`](https://hzliu123.github.io/linux-kernel/Page%20Cache%20in%20Linux%202.6.pdf ),
+calling functions [`swap_readpage` and `swap_writepage`](https://hzliu123.github.io/linux-kernel/Page%20Cache%20in%20Linux%202.6.pdf),
 which are functions responsible for doing IO in swap memory. To collect the exact moment that an access to swap happens,
 the collector attaches `kprobes` for cited functions.
 
@@ -108,91 +461,108 @@ the collector attaches `kprobes` for cited functions.
 
 The following `tracepoints` are used to measure time usage for soft IRQs:
 
-- [`irq/softirq_entry`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_softirq_entry): Called
-   before softirq handler
-- [`irq/softirq_exit`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_softirq_exit): Called when
-   softirq handler returns.
+-   [`irq/softirq_entry`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_softirq_entry): Called
+     before softirq handler
+-   [`irq/softirq_exit`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_softirq_exit): Called when
+     softirq handler returns.
 
 #### Hard IRQ
 
 The following tracepoints are used to measure the latency of servicing a
 hardware interrupt request (hard IRQ).
 
-- [`irq/irq_handler_entry`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_irq_handler_entry):
-  Called immediately before the IRQ action handler.
-- [`irq/irq_handler_exit`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_irq_handler_exit):
-  Called immediately after the IRQ action handler returns.
-- `irq_vectors`: These are traces from `irq_handler_entry` and
-  `irq_handler_exit` when an IRQ is handled. The following elements from vector
-  are triggered:
-    - `irq_vectors/local_timer_entry`
-    - `irq_vectors/local_timer_exit`
-    - `irq_vectors/reschedule_entry`
-    - `irq_vectors/reschedule_exit`
-    - `irq_vectors/call_function_entry`
-    - `irq_vectors/call_function_exit`
-    - `irq_vectors/call_function_single_entry`
-    - `irq_vectors/call_function_single_xit`
-    - `irq_vectors/irq_work_entry`
-    - `irq_vectors/irq_work_exit`
-    - `irq_vectors/error_apic_entry`
-    - `irq_vectors/error_apic_exit`
-    - `irq_vectors/thermal_apic_entry`
-    - `irq_vectors/thermal_apic_exit`
-    - `irq_vectors/threshold_apic_entry`
-    - `irq_vectors/threshold_apic_exit`
-    - `irq_vectors/deferred_error_entry`
-    - `irq_vectors/deferred_error_exit`
-    - `irq_vectors/spurious_apic_entry`
-    - `irq_vectors/spurious_apic_exit`
-    - `irq_vectors/x86_platform_ipi_entry`
-    - `irq_vectors/x86_platform_ipi_exit`
+-   [`irq/irq_handler_entry`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_irq_handler_entry):
+    Called immediately before the IRQ action handler.
+-   [`irq/irq_handler_exit`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_irq_handler_exit):
+    Called immediately after the IRQ action handler returns.
+-   `irq_vectors`: These are traces from `irq_handler_entry` and
+    `irq_handler_exit` when an IRQ is handled. The following elements from vector
+    are triggered:
+    -   `irq_vectors/local_timer_entry`
+    -   `irq_vectors/local_timer_exit`
+    -   `irq_vectors/reschedule_entry`
+    -   `irq_vectors/reschedule_exit`
+    -   `irq_vectors/call_function_entry`
+    -   `irq_vectors/call_function_exit`
+    -   `irq_vectors/call_function_single_entry`
+    -   `irq_vectors/call_function_single_xit`
+    -   `irq_vectors/irq_work_entry`
+    -   `irq_vectors/irq_work_exit`
+    -   `irq_vectors/error_apic_entry`
+    -   `irq_vectors/error_apic_exit`
+    -   `irq_vectors/thermal_apic_entry`
+    -   `irq_vectors/thermal_apic_exit`
+    -   `irq_vectors/threshold_apic_entry`
+    -   `irq_vectors/threshold_apic_exit`
+    -   `irq_vectors/deferred_error_entry`
+    -   `irq_vectors/deferred_error_exit`
+    -   `irq_vectors/spurious_apic_entry`
+    -   `irq_vectors/spurious_apic_exit`
+    -   `irq_vectors/x86_platform_ipi_entry`
+    -   `irq_vectors/x86_platform_ipi_exit`
 
 #### IPC shared memory
 
-To monitor shared memory system call counts, the following `kprobes` are used:
+To monitor shared memory system call counts, Netdata attaches tracing in the following functions:
 
-- `shmget`: Runs when [`shmget`](https://man7.org/linux/man-pages/man2/shmget.2.html) is called.
-- `shmat`: Runs when [`shmat`](https://man7.org/linux/man-pages/man2/shmat.2.html) is called.
-- `shmdt`: Runs when [`shmdt`](https://man7.org/linux/man-pages/man2/shmat.2.html) is called.
-- `shmctl`: Runs when [`shmctl`](https://man7.org/linux/man-pages/man2/shmctl.2.html) is called.
+-   `shmget`: Runs when [`shmget`](https://man7.org/linux/man-pages/man2/shmget.2.html) is called.
+-   `shmat`: Runs when [`shmat`](https://man7.org/linux/man-pages/man2/shmat.2.html) is called.
+-   `shmdt`: Runs when [`shmdt`](https://man7.org/linux/man-pages/man2/shmat.2.html) is called.
+-   `shmctl`: Runs when [`shmctl`](https://man7.org/linux/man-pages/man2/shmctl.2.html) is called.
 
 ### Memory
 
 In the memory submenu the eBPF plugin creates two submenus **page cache** and **synchronization** with the following
 organization:
 
-* Page Cache
-    * Page cache ratio
-    * Dirty pages
-    * Page cache hits
-    * Page cache misses
-* Synchronization
-    * File sync
-    * Memory map sync
-    * File system sync
-    * File range sync
+-   Page Cache
+    -   Page cache ratio
+    -   Dirty pages
+    -   Page cache hits
+    -   Page cache misses
+-   Synchronization
+    -   File sync
+    -   Memory map sync
+    -   File system sync
+    -   File range sync
 
-#### Page cache ratio
+#### Page cache hits
 
-The chart `cachestat_ratio` shows how processes are accessing page cache. In a normal scenario, we expect values around
-100%, which means that the majority of the work on the machine is processed in memory. To calculate the ratio, Netdata
-attaches `kprobes` for kernel functions:
+When the processor needs to read or write a location in main memory, it checks for a corresponding entry in the page cache.
+ If the entry is there, a page cache hit has occurred and the read is from the cache.
 
-- `add_to_page_cache_lru`: Page addition.
-- `mark_page_accessed`: Access to cache.
-- `account_page_dirtied`: Dirty (modified) pages.
-- `mark_buffer_dirty`: Writes to page cache.
+A page cache hit is when the page cache is successfully accessed with a read operation. We do not count pages that were
+added relatively recently.
 
 #### Dirty pages
 
+A "dirty page" is a page in the page cache that was modified after being created. Since non-dirty pages in the page cache
+ have identical copies in secondary storage (e.g. hard disk drive or solid-state drive), discarding and reusing their space
+ is much quicker than paging out application memory, and is often preferred over flushing the dirty pages into secondary storage
+ and reusing their space.
+
 On `cachestat_dirties` Netdata demonstrates the number of pages that were modified. This chart shows the number of calls
 to the function `mark_buffer_dirty`.
 
-#### Page cache hits
+#### Page cache ratio
 
-A page cache hit is when the page cache is successfully accessed with a read operation. We do not count pages that were
-added relatively recently.
+When the processor needs to read or write in a specific memory address, it checks for a corresponding entry in the page cache.
+If the processor hits a page cache (`page cache hit`), it reads the entry from the cache. If there is no entry (`page cache miss`),
+ the kernel allocates a new entry and copies data from the disk. Netdata calculates the percentage of accessed files that are cached on
+ memory. The ratio is calculated counting the accessed cached pages
+ (without counting [dirty pages](#dirty-pages) and pages added because of read misses) divided by total access without dirty pages.
+
+> \_\_**\_\_\_\_**<ins>Number of accessed cached pages</ins>\***\*\_\_\*\***<br/>
+> Number of total accessed pages - dirty pages - missed pages
+
+The chart `cachestat_ratio` shows how processes are accessing page cache. In a normal scenario, we expect values around
+100%, which means that the majority of the work on the machine is processed in memory. To calculate the ratio, Netdata
+attaches `kprobes` for kernel functions:
+
+-   `add_to_page_cache_lru`: Page addition.
+-   `mark_page_accessed`: Access to cache.
+-   `account_page_dirtied`: Dirty (modified) pages.
+-   `mark_buffer_dirty`: Writes to page cache.
 
 #### Page cache misses
 
@@ -213,7 +583,7 @@ changes to a file that was mapped into memory using [`mmap(2)`](https://man7.org
 
 #### File system sync
 
-This chart monitors calls demonstrating commits from filesystem caches to disk. Netdata attaches `kprobes` for
+This chart monitors calls demonstrating commits from filesystem caches to disk. Netdata attaches `tracing` for
 [`sync(2)`](https://man7.org/linux/man-pages/man2/sync.2.html), and [`syncfs(2)`](https://man7.org/linux/man-pages/man2/sync.2.html).
 
 #### File range sync
@@ -240,19 +610,20 @@ By default, MD flush is disabled. To enable it, configure your
 
 To collect data related to Linux multi-device (MD) flushing, the following kprobe is used:
 
--  `kprobe/md_flush_request`: called whenever a request for flushing multi-device data is made.
+-   `kprobe/md_flush_request`: called whenever a request for flushing multi-device data is made.
 
 ### Disk
 
 The eBPF plugin also shows a chart in the Disk section when the `disk` thread is enabled.
 
 #### Disk Latency
+
 This will create the chart `disk_latency_io` for each disk on the host. The following tracepoints are used:
 
-- [`block/block_rq_issue`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_block_rq_issue):
-  IO request operation to a device drive.
-- [`block/block_rq_complete`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_block_rq_complete):
-  IO operation completed by device.
+-   [`block/block_rq_issue`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_block_rq_issue):
+    IO request operation to a device drive.
+-   [`block/block_rq_complete`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_block_rq_complete):
+    IO operation completed by device.
 
 Disk Latency is the single most important metric to focus on when it comes to storage performance, under most circumstances.
 For hard drives, an average latency somewhere between 10 to 20 ms can be considered acceptable. For SSD (Solid State Drives),
@@ -265,6 +636,7 @@ This group has charts demonstrating how applications interact with the Linux ker
 It also brings latency charts for several different filesystems.
 
 #### Latency Algorithm
+
 We calculate the difference between the calling and return times, spanning disk I/O, file system operations (lock, I/O),
 run queue latency and all events related to the monitored action.
 
@@ -275,10 +647,10 @@ To measure the latency of executing some actions in an
 collector needs to attach `kprobes` and `kretprobes` for each of the following
 functions:
 
-- `ext4_file_read_iter`: Function used to measure read latency.
-- `ext4_file_write_iter`: Function used to measure write latency.
-- `ext4_file_open`: Function used to measure open latency.
-- `ext4_sync_file`: Function used to measure sync latency.
+-   `ext4_file_read_iter`: Function used to measure read latency.
+-   `ext4_file_write_iter`: Function used to measure write latency.
+-   `ext4_file_open`: Function used to measure open latency.
+-   `ext4_sync_file`: Function used to measure sync latency.
 
 #### ZFS
 
@@ -286,10 +658,10 @@ To measure the latency of executing some actions in a zfs filesystem, the
 collector needs to attach `kprobes` and `kretprobes` for each of the following
 functions:
 
-- `zpl_iter_read`: Function used to measure read latency.
-- `zpl_iter_write`: Function used to measure write latency.
-- `zpl_open`: Function used to measure open latency.
-- `zpl_fsync`: Function used to measure sync latency.
+-   `zpl_iter_read`: Function used to measure read latency.
+-   `zpl_iter_write`: Function used to measure write latency.
+-   `zpl_open`: Function used to measure open latency.
+-   `zpl_fsync`: Function used to measure sync latency.
 
 #### XFS
 
@@ -298,10 +670,10 @@ To measure the latency of executing some actions in an
 collector needs to attach `kprobes` and `kretprobes` for each of the following
 functions:
 
-- `xfs_file_read_iter`: Function used to measure read latency.
-- `xfs_file_write_iter`: Function used to measure write latency.
-- `xfs_file_open`: Function used to measure open latency.
-- `xfs_file_fsync`: Function used to measure sync latency.
+-   `xfs_file_read_iter`: Function used to measure read latency.
+-   `xfs_file_write_iter`: Function used to measure write latency.
+-   `xfs_file_open`: Function used to measure open latency.
+-   `xfs_file_fsync`: Function used to measure sync latency.
 
 #### NFS