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Modernizing Linux swapping: introducing the swap table

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Re: Modernizing Linux swapping: introducing the swap table

#11

Post by solstice »

ch_123 wrote: post #7
iberator wrote: post #3

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 ran Linux without swap for some years on a laptop with a large-for-the-time amount of RAM (about 8GB). It _mostly_ worked, but sudden spikes of memory usage would render the system unresponsive. Usually it would recover, but it in some cases it required a power cycle. Similarly, on a server where you might expect most of the physical memory to get used, it ends up being very important for stability. Think of VM or…

I had a similar experience with Kubuntu on a xps13 from 2016 with only 8GB of RAM and the system suddenly freezing so hard that a hard reboot was required. While looking for the cause, I noticed that the system had only 250 MB of swap space. After increasing that to 10 GB there have been no further instances of freezing so far.

Re: Modernizing Linux swapping: introducing the swap table

#12

Post by wongarsu »

iberator wrote: post #3

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

It's unloved on Linux because using Linux under memory pressure sucks. But that's not a good reason to abandon improvements. Even more so with the direction RAM prices are headed

Re: Modernizing Linux swapping: introducing the swap table

#13

Post by GCUMstlyHarmls »

ch_123 wrote: post #7
iberator wrote: post #3

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 ran Linux without swap for some years on a laptop with a large-for-the-time amount of RAM (about 8GB). It _mostly_ worked, but sudden spikes of memory usage would render the system unresponsive. Usually it would recover, but it in some cases it required a power cycle. Similarly, on a server where you might expect most of the physical memory to get used, it ends up being very important for stability. Think of VM or…

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 who are wrong.

Re: Modernizing Linux swapping: introducing the swap table

#14

Post by man8alexd »

GCUMstlyHarmls wrote: post #13
ch_123 wrote: post #7

Earlier quoted context omitted.

I ran Linux without swap for some years on a laptop with a large-for-the-time amount of RAM (about 8GB). It _mostly_ worked, but sudden spikes of memory usage would render the system unresponsive. Usually it would recover, but it in some cases it required a power cycle. Similarly, on a server where you might expect most of the physical memory to get used, it ends up being very important for stability. Think of VM or…

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…

8-16-32gb of swap space without cgroup limits would get the system into swap thrashing and make it unresponsive.

Re: Modernizing Linux swapping: introducing the swap table

#15

Post by worldsavior »

FooBarWidget wrote: post #2

One pet peeve I have with virtual memory management on Linux is that, as memory usage approaches 100%, the kernel starts evicting executable pages because technically they're read-only and can be loaded from disk. Thus, the entire system grinds to a halt in a behavior that looks like swapping, because every program that wants to execute instructions has to load its instructions from disk again, only to have those ins…

Program instructions size is small thus loading is fast, so no need to worry about that too much. I'd look on different things first.

Re: Modernizing Linux swapping: introducing the swap table

#16

Post by twic »

worldsavior wrote: post #15
FooBarWidget wrote: post #2

One pet peeve I have with virtual memory management on Linux is that, as memory usage approaches 100%, the kernel starts evicting executable pages because technically they're read-only and can be loaded from disk. Thus, the entire system grinds to a halt in a behavior that looks like swapping, because every program that wants to execute instructions has to load its instructions from disk again, only to have those ins…

Program instructions size is small thus loading is fast, so no need to worry about that too much. I'd look on different things first.

Have you measured this, or is this just an opinion?

Re: Modernizing Linux swapping: introducing the swap table

#17

Post by akdev1l »

robinsonb5 wrote: post #4
FooBarWidget wrote: post #2

One pet peeve I have with virtual memory management on Linux is that, as memory usage approaches 100%, the kernel starts evicting executable pages because technically they're read-only and can be loaded from disk. Thus, the entire system grinds to a halt in a behavior that looks like swapping, because every program that wants to execute instructions has to load its instructions from disk again, only to have those ins…

Indeed. I think what's really needed is some way to mark pages as "required for interactivity" so that nothing related to the user interface gets paged out, ever. That, I think, would go at least some way towards restoring the feeling of "having a computer's full attention" that we had thirty years ago.

Seems the applications can call mlockall() to do this

Re: Modernizing Linux swapping: introducing the swap table

#18

Post by man8alexd »

wongarsu wrote: post #12
iberator wrote: post #3

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

It's unloved on Linux because using Linux under memory pressure sucks. But that's not a good reason to abandon improvements. Even more so with the direction RAM prices are headed

It sucks without proper cgroup limits because swap makes OOM slower to trigger. Either set the cgroup limits or make the swap small.

Re: Modernizing Linux swapping: introducing the swap table

#19

Post by ch_123 »

GCUMstlyHarmls wrote: post #13
ch_123 wrote: post #7

Earlier quoted context omitted.

I ran Linux without swap for some years on a laptop with a large-for-the-time amount of RAM (about 8GB). It _mostly_ worked, but sudden spikes of memory usage would render the system unresponsive. Usually it would recover, but it in some cases it required a power cycle. Similarly, on a server where you might expect most of the physical memory to get used, it ends up being very important for stability. Think of VM or…

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…

I think it's some kind of misplaced desire to be "lightweight" and avoid allocating disk space that cannot be used for regular storage. My motivation way back when for wanting to avoid swap was due to concerns about SSD wear issues, but those have been solved for a long time ago.

Re: Modernizing Linux swapping: introducing the swap table

#20

Post by manuel_w »

GCUMstlyHarmls wrote: post #13
ch_123 wrote: post #7

Earlier quoted context omitted.

I ran Linux without swap for some years on a laptop with a large-for-the-time amount of RAM (about 8GB). It _mostly_ worked, but sudden spikes of memory usage would render the system unresponsive. Usually it would recover, but it in some cases it required a power cycle. Similarly, on a server where you might expect most of the physical memory to get used, it ends up being very important for stability. Think of VM or…

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 same total memory as those with 8 GB of RAM and 8 GB of swap combined.

Then, if I upgrade to 24 GB of RAM, the advice doesn’t change—they still insist on enabling swap. I could install an absurd amount of RAM, and people would still tell me to set up swap space.

It seems that for some, using swap has become dogma. I just don’t see the reasoning. Memory is limited either way; whether it’s RAM or RAM + swap, the total available space is what really matters. So why insist on swap for its own sake?

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