[Bug 27441] Re: Prevent extended periods of thrashing

[John Kennedy]

It's indeed very easy to get thrashing---in my case, 2GB RAM running a
couple of memory-intensive problems like Mathematica and Gimp
Resynthesizer at the same time makes the system almost completely
unresponsive.  I'm talking about Lucid Lynx with all the updates made.
I think for a desktop system, responsiveness is probably the most
important thing, so users should at least have an option to alleviate
this problem, even at the risk of losing some efficiency.  If a program
misbehaves and thrashing starts, I'd like to be able to kill that
program without rebooting and without waiting for hours for the problem
to resolve itself.

Could a developer please tell us more about the technicalities involved?

For instance, what exactly happens during the thrashing?  I understand
the hard drive is running like crazy to move pages in and out of swap
space, but surely preemptive multitasking should mean that the access to
swap space could be paused while other processes get their share of CPU
time, right?  Why, then, can the mouse hang completely for minutes?
Doesn't this mean that the process controlling the display of the mouse
doesn't get to run for minutes at a time?  Why is that allowed at all?
If it is that that process (or memory associated with it) has been paged
out, can't there be a list of priorities for paging, that essentially
prohibits the OS from paging out essential UI elements?

-- 
Prevent extended periods of thrashing
https://bugs.launchpad.net/bugs/27441
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