IndexDisadvantage of SWAPAll about Linux SWAP spaceSize used PriorityImprovementData structure for swapping on Linux systemsLinux is a free and open source operating system that has been in active development since 1991, so most Linux installations suggest include a SWAP partition. This may seem strange to Windows users who are used to having the entire operating system on a single partition. the SWAP partition acts as a memory (RAM) overflow. If the memory is completely full, any additional applications will run from the memory state of the SWAP partition. The exchange is necessary for two important reasons. First, when the system needs more memory than is physically available, the kernel swaps out the least used pages and provides memory to the current application (process) that needs it immediately. Second, a significant number of pages used by an application during the startup phase may only be used for initialization and then never be used again. The system can swap out those pages and free up memory for other applications or even the disk cache. Why do we use SWAP? Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay SWAP partition works like a RAM overflow While your memory is completely full Increases the amount of usable memory without actually getting more RAMA partitions SWAP also supports moving some items from memory Can move rarely needed items away from high-speed memory Disadvantage of SWAP Takes up hard disk space as SWAP partition does not change size dynamically. It is necessary to improve performance. All About Linux SWAP Space Linux has two forms of swap space: the swap partition and the swap file. The swap partition is an independent part of the hard drive used only for swap; no other files can occupy there. Swap file is a special file in the filesystem that occupies between the system and data files. To see how much swap space you have, use the swapon -s command. The output will look like this: Size Priority Used Each line lists a different swap space used by the system. Now, the "Type" field indicates that this swap space is a partition rather than a file, and from "File Name" we see that it is located on the sda5 disk. The "Size" is listed in kilobytes and the "Used" field indicates how many kilobytes of swap space have been used, but in this example there is none. 'Priority' tells Linux which swap space to use first. One great thing about the Linux swap subsystem is that if you mount two or more swap spaces (preferably on two different devices) with the same priority, Linux will interleave its swap activity between them, which can significantly increase the performance of exchange. To add another swap partition to your system, you must first provide it. The first step is to make sure the partition is marked as a swap partition and the second step is to create the swap filesystem. To verify that the partition is marked for swap, run as root:Fdisk -l /dev/ hdb replace /dev/hdb with your system's hard disk device on which the swap partition is located. You should see output similar to the following: Device Boot Start End Blocks Id System/dev/hdb1 2328 2434 859446 82 Linux swap / Solaris If the partition is not visible as swap, you will need to modify it by running fdisk and using the 't' command menu option . be careful when working with partitions: you don't want to delete important partitions by mistake or change the system partition id to swap by mistake. All data on a swap partitionthey will be destroyed, so double-check any changes you make. Also note that Solaris uses the same swap space ID as Linux for its partitions, so be careful not to kill your Solaris partitions by accident. At that time a partition is marked as swap, you need to prepare it using mkswap (make swap) command as root: mkswap /dev/hdb1 If you see no errors, your swap space is ready to use. To start it immediately, type: swapon /dev/hdb1 You can test that it is in use by running swapon -s. To automatically mount swap space at startup, you need to add an entry to the /etc/fstab file, which contains a list of filesystems and swap spaces that should be mounted at startup. The format of each line is: Since swap space is a special type of filesystem, many of these parameters are not suitable. For swap space, add: /dev/hdb1 none swap sw 0 0, where /dev/hdb1 is the swap partition. It has no specific mount point, from now on none. It is of type swap with sw options and the last two parameters are not used, so they are entered as 0. To verify that the swap space is mounted automatically without having to restart the computer, you can run swapoff - a command (which turns off all swap spaces) and then swapon -a (which mounts all the swap spaces listed in the /etc/fstab file) and then check it with swapon -s.Swap space location. Swap space can be taken from the normal file system or in a different disk partition. A large file within the file system: simple but inefficient. Navigating the directory structure and location data structure of the disk requires time and potentially additional disk accesses. External fragmentation can significantly increase swap times by forcing multiple lookups when reading or writing a process image Improved Caching of block location information in main memory Contiguous allocation for the swap file, but the cost of FS data structure traversal still remains In a different partition: raw partition Creates swap space during disk partitioningA different swap space storage manager is used to allocate and deallocate blocks. Use optimization algorithms for speed, rather than storage scheduling. Internal fragment could increase Linux supports both approaches The SWAP space management example: Solaris 1Text segment pages are imported from the file system and are thrown away if selected for pagination. More efficient to read back from FS than write it to SWAP space. Swap Space: Used only as backup storage for unnamed memory pages Solaris 2 Allocates SWAP space only when a page is moved from physical memory Not when the virtual memory page is first created. Data Structure for Swapping on Linux Systems In addition to the swap partition, Linux also supports a swap file that you can create, prepare, and mount in a similar way to a swap partition. The advantage of swap files is that you don't need to find an empty partition or re-partition a disk to add additional swap space. To create a swap file, use the dd command to create an empty file. To create a 1 GB file, type: dd if=/dev/zero of=/swapfile bs=1024 count=1048576/swapfile is the name of the swap file and count of 1048576 is the size in kilobytes. Prepare the swap file using mkswap just like you would a partition, but this time use the name of the swap file: mkswap /swapfileAnd mount it using the swapon command: swapon /swapfile. The /etc/fstab entry for a swap file would look like this: /swapfile.