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What is "actively used"? The bash session that I was using 2 seconds before system grinded to a halt sure didn't count.
Your bash session is most likely still in memory but the system is spending 99.9% of time waiting for swap I/O, trying to free a few pages of memory. Swap random access latency is 10^3 slower than RAM.
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Your bash session is most likely still in memory but the system is spending 99.9% of time waiting for swap I/O, trying to free a few pages of memory. Swap random access latency is 10^3 slower than RAM.
The system has swap disabled.
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> To be honest I don't know why it's such an issue on Linux. edit: I wrote all this before realizing I overlooked that you answered it yourself, so below is my very elaborate explanation of what you said: > Windows presumably because it doesn't over-commit memory. I'm no expert but from what I've gathered this ultimately boils down to how Linux went with fork for multiprocessing, vs Windows focused on threads. With f…
> However in almost all normal cases, this grossly overestimates the required memory and thus leads to swapping when technically it is not needed. This is not true. Disabling overcommit doesn't change reclaim and swapping behaviour and doesn't lead to unnecessary swapping.
Yeah that wasn't correct. It will however cause the kernel to refuse memory allocations[1] which could have been allowed, and a lot of programs don't handle that gracefully.
[1]: https://www.kernel.org/doc/html/v6.13/mm/overcommit-accounti...
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I don't mean interactivity within apps, per se - I mean the desktop and underlying OS, so that if an electron app goes unresponsive and eats all the free RAM the window manager can still kill it. Or you can still open a new terminal window, log in and kill it. Right now it can take several minutes to get a Linux system back under control once a swapstorm starts.
Alt+[SysRq,f] Or Alt+[SysRq,h] for help
In 30 years of using desktop Linux I've never been able to interrupt a swapstorm. The only way out is long-press the power button.
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I dont get why anti-swap is so prevalent in Linux discussions. Like, what does it hurt to stick 8-16-32gb extra "oh fuck" space on your drive. Either you're going to never exhaust your system ram, so it doesn't matter, minimally exhaust it and swap in some peak load but at least nothing goes down, or exhaust it all and start having things get OOM'd which feels bad to me. Am I out of touch? Surely it's the children wh…
The pro-swap stance has never made sense to me because it feels like a logical loop. There’s a common rule of thumb that says you should have swap space equal to some multiple of your RAM. For instance, if I have 8 GB of RAM, people recommend adding 8 GB of swap. But since I like having plenty of memory, I install 16 GB of RAM instead—and yet, people still tell me to use swap. Why? At that point, I already have the s…
Once the system has used all available RAM if has for disk cache it has a choice if it has swap. It can write write modified RAM to swap, and use the space it freed for disk cache. There is invariably some RAM where that tradeoff works - RAM use by login programs, and other servers that haven't been accessed in hours. Assuming the system is tuned well, that is all that goes to swap. The freed RAM is then used for disk cache, and your system runs faster - merely because you added swap.
There is no penalty for giving a system too much swap (apart from disk space), as the OS will just use it up until the tradeoff doesn't make sense. If your system is running slow because swap is being overused the fix isn't removing swap (if you did you system may die because of lack of RAM), it's to add RAM until swap usage goes down.
So, the swap recipe is: give your system so much swap you are sure it exceeds the size of stuff that's running but not used. 4Gb is probably fine for a desktop. Monitor it occasionally, particularly if your system slows down. If swap usage ever goes above 1Gb, you probably need to add RAM.
On servers swap can be used to handle DDOS from malicious logins. I've seen 1000's of ssh attempts happen at once, in an attempt to break in. Eventually the system will notice and firewall the IP's doing it. If you don't have swap, those login's will kill the system unless you have huge amounts of RAM that isn't normally used. With swap it slows to a crawl, but then recovers when the firewall kicks in. So both provisioning swap and having loads of RAM prevent DDOS's from killing your system, but this is in a VM, one costs me far more per month than the other, and I'm trying fix to a problem that happens very rarely.
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It's not like it's easy to shuffle partitions around. Swap files are a pain, so you need to reserve space at the end of the table. By the time you need to increase swap the previous partition is going to be full. Better overcommit right away and live with the feeling you're wasting space.
> Swap files are a pain Easier than partitions: mkswap --size 2G --file swap.img swapon swap.img
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It's not like it's easy to shuffle partitions around. Swap files are a pain, so you need to reserve space at the end of the table. By the time you need to increase swap the previous partition is going to be full. Better overcommit right away and live with the feeling you're wasting space.
Exactly opposite. Don't use swap partitions, and use swap files, even multiple if necessary. Never allocate too much swap space. It is better to get OOM earlier then to wait for unresponsive system.
Swap file means fallocating, setting extended attributes (like `nocow`), finding file offset and writing it to kernel params, and other gotchas, like btrfs not allowing snapshotting a subvolume with an active swap file.
Technically it's preferable, won't argue with that.
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The pro-swap stance has never made sense to me because it feels like a logical loop. There’s a common rule of thumb that says you should have swap space equal to some multiple of your RAM. For instance, if I have 8 GB of RAM, people recommend adding 8 GB of swap. But since I like having plenty of memory, I install 16 GB of RAM instead—and yet, people still tell me to use swap. Why? At that point, I already have the s…
It's true that if you always have free RAM, you don't need swap. But most people don't have that it can always be used as a disk cache. Even if you are just web browsing, the browser is writing to disk stuff fetched from the internet in the hopes it won't change, the OS is will be keeping all of that in RAM until no more will fit. Once the system has used all available RAM if has for disk cache it has a choice if it…
There is a huge penalty for having too much swap - swap thrashing. When the active working set exceeds physical memory, performance degrades so much that the system becomes unresponsive instead of triggering OOM.
> Monitor it occasionally, particularly if your system slows down.
Swap doesn't slow down the system. It either improves performance by freeing unused memory, or it is a completely unresponsive system when you run out of memory. Gradual performance degradation never happens.
> give your system so much swap you are sure it exceeds the size of stuff that's running but not used. 4Gb is probably fine for a desktop.
Don't do this. Unless hibernation is used, you only need a few hundred megabytes of free swap space.
Another useless feature into Linux kernel. Who uses swap space nowadays?! Last time I used swap on Linux device was around Pentium 2 era but in reality closer to 486DX era
I rely on it heavily. Have you tried zram swap?