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Under high load, top/ps/procinfo stop updating, while other applications seem to keep running (slowly, of course.) top can lock up and stop updating for two to three minutes at a time! I would hope that psutils would be no less responsive under load, as that's basically the only way to rescue a box that is thrashing to death.
We (Red Hat) should really try to fix this before next release.
A fix for this is in Linus kernel 2.4.3-pre8 Unfortionatly, this fix has caused major instabilities. We're hoping to get a stable fix as soon as possible
I don't think 2.4.3 fixed it, as 2.4.5-0.2.9 is no better than the 7.1-release kernel. I've attached a python script to help demonstrate the problem. Run this script in one terminal and wait for it to stop spawning threads; after it's done, run a ps aux in another terminal. Alternately, if you have *alot* of patience, try starting top in another terminal. It's not nearly so bad under normal circumstances, but in any case ps and top aren't very useful under high load. FreeBSD does quite well on this test compared to Linux 2.4.
Created attachment 20803 [details] spawn.py
It turns out this problem is caused by VMA fragmentation in heavily threaded processes. Watching ps output, there's a marked slowdown as it prints stats for threads. glibc issue? Kernel issue? Who knows. For now, don't run lots of threads on Linux ...