Swap space is an area of the hard disk that serves as an overflow when the computer memory is full. The memory used by inactive applications is partially written out to disk to make room for other applications and for the disk cache for active files.

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Why use swap when there is more than enough free space in RAM?

Using swap space instead of RAM can drastically slow down a PC. So why, when I have more than enough RAM available, does my Linux system (Arch) use the swap? Checkout my conky output below: Also, ...
57
votes
12answers
11k views

Do I need swap space if I have more than enough amount of RAM?

From what I understand, the purpose of a swap partition in Linux is to free up some "not as frequently accessed" information from RAM and move it to a specific partition on your harddrive (at the cost ...
52
votes
3answers
5k views

What NOT to put on an SSD?

I bought an SSD and I am going to set up my desktop system with a completely fresh Linux installation. SSDs are known to be fast, but they have a disadvantage: The number of writes (per block?) is ...
37
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2answers
23k views

Why is swappiness set to 60 by default?

I just read some stuff about swappiness on Linux. I don't understand why the default is set to 60. According to me this parameter should be set to 10 in order to reduce swap. Swap is on my hard ...
37
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9answers
2k views

Is swap an anachronism?

I've used unix for quite a while, and for the last couple years I've felt like swap is an anachronism, but I'd be curious what other folks think. My argument is roughly this (assuming no global ...
31
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2answers
28k views

How can I check if swap is active from the command line?

How can I check if swap is active, and which swap devices are set up, on the command line?
29
votes
3answers
10k views

Are there any side effects when two distros share a swap partition?

In order to save disk space, I want to have two OS installations share a single swap partition (a dual-boot). Is this a good idea?
26
votes
12answers
3k views

How can I tweak my Linux desktop to be more responsive?

I have the experience that Linux works fine until the physical memory is exhausted. As soon as swap space is used the performance is severely degraded and the GUI becomes unresponsive. This problem ...
25
votes
4answers
6k views

How can swapoff be that slow?

Somehow I happened to swap out 14 GB of memory. After having killed the culprit, I have tons of free memory again, so I thought I could bring in the important data again. So with 5 GB out of 32 GB ...
24
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3answers
5k views

What does the vm.swappiness parameter really control?

Per the kernel documentation: This control is used to define how aggressive the kernel will swap memory pages. Higher values will increase aggressiveness, lower values decrease the amount of swap. ...
21
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4answers
38k views

How to completely disable swap?

I am using Debian sid, hard drive formatted with ext4, running on linux 3.1 I remember on previous linux versions (maybe before 3.0), if I run out of memory, and swap is not enabled, programs will ...
21
votes
4answers
922 views

Making Linux read swap back into memory

The Linux kernel swaps out most pages from memory when I run an application that uses most of the 16GB of physical memory. After the application finishes every action (typing commands, switching ...
20
votes
3answers
7k views

Why does Linux use a swap partition rather than a file?

It seems to me a swap file is more flexible.
20
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1answer
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per process swapiness for linux

/proc/sys/vm/swappiness is nice but i want a knob that's per process like /proc/$PID/oom_adj so that i can make certain processes less likely than others to have any of their pages swapped out unlike ...
18
votes
6answers
3k views

How to safely turn off swap permanently? (on Debian Jessie)

I fresh installed Debian Jessie with default partitioning on an SSD drive. My current disk partitions look like this: As I have 16GB RAM, I think I don't need swap. On Windows, I had it turned off ...
15
votes
4answers
7k views

How to re-load all running applications from swap space into RAM?

If my desktop run out of memory and swaps a lot then I free or kill the application wasting my RAM. But, after that, all my desktop/applications have been swapped and are horribly slow, do you know a ...
15
votes
2answers
3k views

Linux: Total swap used = swap used by processes +?

So, I'm trying to do some investigation on where does swap use come from in a system with high swap usage: # free total used free shared buffers cached Mem: ...
13
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3answers
3k views

What is the purpose of multiple swap files

During installation of most (if not all) distro's of linux, the hard drive is partitioned to include a swap partition by default. It is possible to change this behavior with swapon -p priority ...
12
votes
1answer
10k views

How to test swap partition

I'm trying to diagnose some random segfaults on a headless server and one thing that seems curious is that they only seem to happen under memory pressure and my swap size will not go above 0. How can ...
11
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6answers
4k views

Can Linux “run out of RAM”?

I saw several posts around the web of people apparently complaining about a hosted VPS unexpectedly killing processes because they used too much RAM. How is this possible? I thought all modern OS' ...
11
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1answer
8k views

swapon: Operation not permitted

I'm running this as root, obviously. I've created a file called /swap/sw1, by dumping 512 megs of /dev/zero into it. I then ran mkswap, which said: Setting up swapspace version 1, size = 524284 KiB ...
11
votes
2answers
148 views

how to check what is in swap?

On my system i have some amount of swap used: undefine@uml:~$ free total used free shared buffers cached Mem: 16109684 15848264 261420 633496 ...
10
votes
4answers
172 views

Can swapping be disabled on the application level?

I'm currently using thunderbird with gnupg to read encrypted emails. If I understand the swapping behavior correctly, the memory pages containing the decrypted emails might be swapped out and leave ...
10
votes
1answer
599 views

What happens to data in swap when your computer hibernates?

When a computer goes into hibernation mode, it saves the contents of the RAM into the swap space so that it can resume exactly where it left off when it powers back on. So, what if you are currently ...
9
votes
2answers
2k views

How do I set up an encrypted swap file in Linux?

How do I set up an encrypted swap file (not partition) in Linux? Is it even possible? All the guides I've found talk about encrypted swap partitions, but I don't have a swap partition, and I'd ...
9
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3answers
9k views

Where to put swap space, at beginning or end and other swap questions

Where do I put my swap? Debian installation gives 2 choices: (1) at the end or (2) at the beginning of the disk space. What is optimal? What is the optimal amount of swap given my computer has ...
8
votes
2answers
6k views

Cleancache vs zram?

I have an old laptop here with only 512 MB of RAM. Since a few kernel releases, I am using zram to convert 256 MB of it to a compressed ramdisk which is then used as swap. This has proved to be very ...
8
votes
2answers
305 views

How can my HDD swap without a swap partition?

I have no swap partition on my disk because I prefer having the OOM reaper kill anything it wants quickly rather than having to wait 10 minutes for my swap partition to get filled + 5 other minutes to ...
8
votes
3answers
705 views

Why does it makes sense to cache swap?

It sounds quite counter-productive to me to cache pages that are swapped out. If you swap pages in, what is the advantage to first cache them in memory, only to have to than move them to the right ...
8
votes
1answer
204 views

What sets the size of tmpfs? What happens when its full?

What sets the size of the tmpfs? (On my machine it resides in /dev/shm) I can see its entry in /etc/fstab, but no notation of its size. When checking with df -h, it seems to be half the size of the ...
8
votes
1answer
3k views

Zswap, Zram, Zcache desktop usage scenarios

I've been trying to understand the difference in use cases for Zswap, Zram, and Zcache. Apologies in advance for the long/slightly sloppily worded question. I've done a bunch of googling, and I ...
8
votes
1answer
3k views

Tmpfs only with RAM

How to be sure that a tmpfs filesystem can only deal with physical and it's not using a swap partition on disk ? Since i have a slow HDD and a fast RAM i would like, at least, giving higher priority ...
7
votes
3answers
3k views

How to set up properly zram and swap

I'm configuring & compiling new 3.0 kernel. One of the goodies I planned to use for some time (by patching) that was merged into 3.0 is zram. Is it possible to set both hdd swap and zram swap so ...
7
votes
2answers
182 views

How to make files inside TMPFS more likely to swap

I'm using tmpfs for my /tmp directory. How can I make the computer decide to swap out the files inside the /tmp before swapping out anything that is being used by applications? Basically the files ...
7
votes
1answer
142 views

Can swap be encrypted per user?

The problem arises for a multiuser computer with encrypted swap, as to how to allow each user to hibernate and resume from hibernation without compromising the security of the other users. I'm ...
7
votes
2answers
3k views

What is the appropriate value of vm.swappiness when using zram?

I'm using zram on my computer as a compressed RAM-backed swap. When the system needs to swap something out, swapping it to a zram-backed swap file is more or less equivalent to compressing that data ...
6
votes
1answer
1k views

what does “Read Swap Header failed: Success” mean?

I'm trying to install Arch Linux (from the 2014-04-01 snapshot). I've made a swap file and tried to swapon it, but I got an error(?) message I don't understand. I've executed fallocate -l 512M ...
6
votes
1answer
215 views

How can I tell how much my system is swapping?

Is there a good way to see how much my system (for example how frequently, how much swap space it is using each time/ on average) is using the swap space during various tasks?
6
votes
3answers
1k views

How can I open a file in VIM in readonly mode if it already has a swapfile?

When I use the command :e filename to open a file and this file is already opened by another vim instance, I get a prompt asking me if I want to open the file in read-only mode, edit anyway, recover, ...
6
votes
1answer
291 views

Can I accelerate swap by using multiple harddrives?

I still have two old ATA drives (one is only 8GB, one is somewhat defect) and I've been thinking about putting them into my PC and activating swap on them, too. What will be effect of this? Will my ...
6
votes
3answers
15k views

Swap usage too high?

I have a debian sid box, freshly installed about a month ago, with no desktop apps running at the moment. Any command I try to run (via ssh) makes the hard disk work very hard. The system worked ...
6
votes
1answer
235 views

Is there any relationship between memory fragmentation and whether or not swap is enabled on a system?

One of the answers to Do I need swap space if I have more than enough amount of RAM? got me wondering if there is any relationship between memory fragmentation as measured by cat /proc/buddyinfo and ...
6
votes
2answers
242 views

GNU/Linux swapping blocks system

I have used GNU/Linux on systems from 4 MB RAM to 512 GB RAM. When they start swapping, most of the time you can still log in and kill off the offending process - you just have to be 100-1000 times ...
5
votes
2answers
6k views

Does changing of the swappiness need a reboot?

If I configure the swappiness value to another, from ex.: 60 to 0, then I always need to reboot the machine to the changes to take effect? Even when modifying with: sysctl -w vm.swappiness=0
5
votes
1answer
236 views

When does swap start to be used? When does a process get an out of memory error and be killed?

When does swap start to be used? Is it when the memory is fully used? Or when the memory hasn't been fully used? When does a process get an "Out of memory" error and be killed by the kernel? is it ...
5
votes
1answer
4k views

What command can be used to force release everything in swap partition back to memory?

What command can be used to force release everything in swap partition back to memory ? Presume that I have enough memory.
5
votes
2answers
1k views

Linux (3.4) SSD swap partition usage causes extreme latency - how to eliminate?

I'm running on 4G RAM with an extra 6G swap partition, SSD is a pretty decent SAMSUNG MZMPA128HMFU model. System responds very well to workloads when things stay in RAM, but as soon as things reach ...
5
votes
2answers
2k views

Does swap need to be on a contiguous LVM logical volume

I am setting up a machine to run a number of virtual machines. I am using a single HDD with a boot partition and an LVM partition. I read on the Arch wiki that logcial volumes which will be used for ...
5
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1answer
3k views

Swap partition in LVM?

I was wondering if putting the swap partition into a logical volume group has any drawbacks (e.g. performance), or would it be "just the same" as having it as a separate primary/logical partition? I ...
5
votes
1answer
224 views

can initramfs be paged out to swap disk?

I am using initramfs to boot Centos via PXE. The initramfs used memory is listed within the "cached" value in /proc/meminfo or via free. Since I need to calculate performance data, I need to know ...