Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space.
While swap space can help machines with a small amount of RAM, it should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a slower access time than physical memory. Swap space can be a dedicated swap partition (recommended), a swap file, or a combination of swap partitions and swap files. Note that Btrfs does not support swap space.
In years past, when memory was expensive, so the recommended amount of swap space increased linearly with the amount of RAM in the system. However, modern systems often include hundreds of gigabytes of RAM. As a consequence, recommended swap space is considered a function of system memory workload, not system memory.
In the table below, it provides the recommended size of a swap partition depending on the amount of RAM in your system and whether you want sufficient memory for your system to hibernate. The recommended swap partition size is established automatically during installation. To allow for hibernation, however, you need to edit the swap space in the custom partitioning stage.

Recommended System Swap Space

Amount of RAM in the system Recommended swap space Recommended swap space
if allowing for hibernation
⩽ 2 GB 2 times the amount of RAM 3 times the amount of RAM
> 2 GB– 8 GB Equal to the amount of RAM 2 times the amount of RAM
> 8 GB – 64 GB At least 4 GB 1.5 times the amount of RAM
> 64 GB At least 4 GB Hibernation not recommended

At the border between each range listed in Table above,  for example a system with 2 GB, 8 GB, or 64 GB of system RAM, discretion can be exercised with regard to chosen swap space and hibernation support. If your system resources allow for it, increasing the swap space may lead to better performance. A swap space of at least 100 GB is recommended for systems with over 140 logical processors or over 3 TB of RAM.


Note

The distributing swap space over multiple storage devices also improves swap space performance, particularly on systems with fast drives, controllers, and interfaces.
Important
File systems and LVM2 volumes assigned as swap space should not be in use when being modified. Any attempts to modify swap fail if a system process or the kernel is using swap space. Use the free and cat /pro c/swaps commands to verify how much and where swap is in use.
You should modify swap space while the system is booted in rescue mode, see Booting Your Computer in Rescue Mode in the Red Hat Enterprise Linux 7 Installation Guide. When prompted to mount the file system, select Skip.