What is vm.max_map_count in linux Systems?

In the context of Linux systems, vm.max_map_count is a sysctl parameter that defines the maximum number of memory map areas a process can have. Here's a more detailed explanation:

Memory Mapping:

Memory mapping is a technique that allows a process to access files or devices as if they were part of its virtual memory. This is done by mapping a file or device into the process's address space.   

vm.max_map_count:

This sysctl setting limits the number of these memory map areas that a single process can create.   

It's important because some applications, particularly those that heavily utilize memory-mapped files (like databases such as Elasticsearch), may require a higher max_map_count value.

Why It Matters:

If an application attempts to create more memory map areas than the vm.max_map_count limit allows, it can lead to errors or unexpected behavior, such as "out of memory" exceptions.

Therefore, in certain situations, it becomes necessary to increase this value.   

Practical Usage:

You can check the current value of vm.max_map_count using the command sysctl vm.max_map_count.

To change the value temporarily, you can use sysctl -w vm.max_map_count=<new_value>.

To make the change persistent across reboots, you can add the setting vm.max_map_count=<new_value> to the /etc/sysctl.conf file (or files within /etc/sysctl.d/).

In essence, vm.max_map_count is a kernel parameter that controls the maximum number of memory map areas a process can have, and it's often adjusted to accommodate the requirements of memory-intensive applications.