5 ms·

What is the "correct" handling of swap on an HDD supposed to be like? It is going to be slow no matter what you do. Windows also locks up for long periods of ti

by opencl 8y ago

What is the "correct" handling of swap on an HDD supposed to be like? It is going to be slow no matter what you do. Windows also locks up for long periods of time if you use up almost all the RAM and it has to swap to HDD.

Dayshine 8y ago
When I say lock up I mean the UI completely stops. As in, my i3 bar stops updating for several minutes. Not even the linux magic commands let me recover. On windows things may be unresponsive, but at least ctrl-alt-del responds, and at least the mouse moves! The main difficulty is I can't tell if my machine has crashed vs is overloaded if the UI doesn't do anything for several minutes.
- zozbot123 8y ago
  If you renice the UI processes to a higher-than-normal priority, it should work more like it does in Windows. (This used to be somewhat risky, but today Linux UI is not going to hog your system resources.) The underlying problem is that when memory is tight, Linux starts evicting "clean" pages from the page cache that actually will need to be accessed shortly afterwards (i.e. they're part of the working set of some running process), and thrashing occurs. There's no easy solution to this issue, other than making user programs more responsive to memory pressure in the first place. (This could extend as far as some sort of seamless checkpoint+resume support, like what you see in mobile OS's today.)
  - Dayshine 8y ago
    >There's no easy solution to this issue, other than making user programs more responsive to memory pressure in the first place. Well, why can't distributions that come with recommended GUIs just set that high-than-normal priority by default? I don't quite understand why the system can't keep what it needs to perform REISUB in memory at all times. Surely that's a tiny program!?
    - zozbot123 8y ago
      > Well, why can't distributions that come with recommended GUIs just set that high-than-normal priority by default? Feel free to file bugs for your preferred distro. It would be especially appropriate to do this for critical UI processes like xorg/wayland or lightdm, and for "lightweight" desktops like xfce/lxde that aren't going to cause resource pressure under foreseeable conditions, even when run at higher-than-normal priority.
- pritambaral 8y ago
  > Not even the linux magic commands let me recover. Are you sure you've set up the magic sysctls correctly? Ubuntu ships with magic oomkill disabled, by default. On all machines I've tried, whenever I've needed it, magic oomkill has always worked, and I've been thankful of the fact that it's implemented down in the kernel.
Dylan16807 8y ago
"Correct" handling of swap would mean mostly leaving the window manager and its dependencies in memory. Individual application windows may stop responding, but everything else should be pretty quick. And small things like terminal emulators should get priority to stay in ram too.
ninkendo 8y ago
Not that I'd recommend this, but my work MBP has 16GB of ram, and my typical software development setup (JVM, IntelliJ, Xcode, gradle) easily uses up 30GB. It swaps a lot but generally OSX does a good job of keeping the window manager and foreground applications at priority so I can still use my machine while this is happening. I attribute this to the fact that the darwin kernel has a keen awareness of what threads directly affect the user interface and which do not (even including the handling of XPC calls across process boundaries... if your work drives the UI, you get scheduling/RAM priority). I don't think the linux kernel has nearly this level of awareness.
- zozbot123 8y ago
  > ... the darwin kernel has a keen awareness of what threads directly affect the user interface and which do not (even including the handling of XPC calls across process boundaries... if your work drives the UI, you get scheduling/RAM priority). I don't think the linux kernel has nearly this level of awareness. You're talking about priority inheritance in the kernel. In Linux, this is in development as part of the PREEMPT_RT ("real-time") patches, already available experimentally in a number of distributions.

by opencl 8y ago

Dayshine 8y ago

When I say lock up I mean the UI completely stops. As in, my i3 bar stops updating for several minutes. Not even the linux magic commands let me recover. On windows things may be unresponsive, but at least ctrl-alt-del responds, and at least the mouse moves! The main difficulty is I can't tell if my machine has crashed vs is overloaded if the UI doesn't do anything for several minutes.

zozbot123 8y ago
If you renice the UI processes to a higher-than-normal priority, it should work more like it does in Windows. (This used to be somewhat risky, but today Linux UI is not going to hog your system resources.) The underlying problem is that when memory is tight, Linux starts evicting "clean" pages from the page cache that actually will need to be accessed shortly afterwards (i.e. they're part of the working set of some running process), and thrashing occurs. There's no easy solution to this issue, other than making user programs more responsive to memory pressure in the first place. (This could extend as far as some sort of seamless checkpoint+resume support, like what you see in mobile OS's today.)
- Dayshine 8y ago
  >There's no easy solution to this issue, other than making user programs more responsive to memory pressure in the first place. Well, why can't distributions that come with recommended GUIs just set that high-than-normal priority by default? I don't quite understand why the system can't keep what it needs to perform REISUB in memory at all times. Surely that's a tiny program!?
  - zozbot123 8y ago
    > Well, why can't distributions that come with recommended GUIs just set that high-than-normal priority by default? Feel free to file bugs for your preferred distro. It would be especially appropriate to do this for critical UI processes like xorg/wayland or lightdm, and for "lightweight" desktops like xfce/lxde that aren't going to cause resource pressure under foreseeable conditions, even when run at higher-than-normal priority.
pritambaral 8y ago
> Not even the linux magic commands let me recover. Are you sure you've set up the magic sysctls correctly? Ubuntu ships with magic oomkill disabled, by default. On all machines I've tried, whenever I've needed it, magic oomkill has always worked, and I've been thankful of the fact that it's implemented down in the kernel.

Dylan16807 8y ago

"Correct" handling of swap would mean mostly leaving the window manager and its dependencies in memory. Individual application windows may stop responding, but everything else should be pretty quick. And small things like terminal emulators should get priority to stay in ram too.

ninkendo 8y ago

Not that I'd recommend this, but my work MBP has 16GB of ram, and my typical software development setup (JVM, IntelliJ, Xcode, gradle) easily uses up 30GB. It swaps a lot but generally OSX does a good job of keeping the window manager and foreground applications at priority so I can still use my machine while this is happening. I attribute this to the fact that the darwin kernel has a keen awareness of what threads directly affect the user interface and which do not (even including the handling of XPC calls across process boundaries... if your work drives the UI, you get scheduling/RAM priority). I don't think the linux kernel has nearly this level of awareness.

zozbot123 8y ago
> ... the darwin kernel has a keen awareness of what threads directly affect the user interface and which do not (even including the handling of XPC calls across process boundaries... if your work drives the UI, you get scheduling/RAM priority). I don't think the linux kernel has nearly this level of awareness. You're talking about priority inheritance in the kernel. In Linux, this is in development as part of the PREEMPT_RT ("real-time") patches, already available experimentally in a number of distributions.