Modernizing Linux swapping: introducing the swap table
1–10 of 132 posts
Re: Modernizing Linux swapping: introducing the swap table
#2One 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 instruction pages be evicted again when context switching to another program. This behavior is especially counter intuitive because disabling swap does not prevent this problem. There are no convenient settings for administrators for preventing this problem.
It's good that we have better swapping now, but I wish they'd address the above. I'd rather have programs getting OOMKilled or throwing errors before the system grinds to a halt, where I can't even ssh in and run 'ps'.
Re: Modernizing Linux swapping: introducing the swap table
#3Another 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
Re: Modernizing Linux swapping: introducing the swap table
#4One 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.
Re: Modernizing Linux swapping: introducing the swap table
#5Another 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
We use it in production.
Workloads with unpredictable memory usage (32Mb to 4Gb per process), but we also want to start enough processes to saturate the CPU.
Before we configured & enabled swap we were either sitting at low CPU utilisation or OOM
Re: Modernizing Linux swapping: introducing the swap table
#6Another 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 is still useful for many workloads, I use it in work and on my own machines
Re: Modernizing Linux swapping: introducing the swap table
#7Another 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 container hosts in particular.
Re: Modernizing Linux swapping: introducing the swap table
#8One 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…
Linux swap has been fixed on Chromebooks for years thanks to MGLRU. It's upstream since Linux 6.1 and you can try it with
echo y >/sys/kernel/mm/lru_gen/enabledRe: Modernizing Linux swapping: introducing the swap table
#9Another 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
You should still use swap. It's not "2x RAM" as advice anymore, and hasn't been for years: https://chrisdown.name/2018/01/02/in-defence-of-swap.html
tl;dr; give it 4-8GB and forget about it.
Re: Modernizing Linux swapping: introducing the swap table
#10One 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…
Actively used executable pages are explicitly excluded from reclaim. And if they are not used, why should they stay in memory when the memory is constrained? It is not the first time I have heard complaints about executable pages, but it seems to be some kind of common misunderstanding.