Hi VM/procfs hackers,
System is UP Athlon 700mhz with 256mb ram running vanilla 2.4.0-test10.
gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)
I'd like to report what seems like a performance problem in the latest
kernels. Actually, all recent kernels have exhibited this problem, but
I was waiting for the new VM stuff to stabilize before reporting it.
My test is: run 7 processes that each allocate and randomly access 32mb
of ram (on a 256mb machine). Even though 7*32MB = 224MB, this still
sends the machine lightly into swap. The machine continues to function
fairly smoothly for the most part. I can do filesystem operations, run
new programs, move desktops in X etc.
Except: programs which access /proc/<pid>/stat stall for an inderminate
amount of time. For example, 'ps' and 'vmstat' stall BADLY in these
scenarios. I have had the stalls last over a minute in higher VM
Unfortunately, when system is thrashing, it's nice to be able to run
'ps' in order to get the PID to kill, and run a reliable vmstat to
Here's a segment of an strace of 'ps' showing a 12 second stall (this
isn't the worst I've seen by any means, but a 12 second stall trying to
get process info for 1 swapping task can easily snowball into a DOS).
0.000119 open("/proc/4746/stat", O_RDONLY) = 7
0.000072 read(7, "4746 (hog) D 4739 4739 827 34817"..., 511) = 181
12.237161 close(7) = 0
The wchan of the stalled 'ps' is in __down_interruptible, which probably
doesn't help much.
This worked absolutely fine in 2.2. Even under extreme swap pressure,
vmstat continues to function fine, spitting out messages every second as
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This archive was generated by hypermail 2b29 : Tue Nov 07 2000 - 21:00:09 EST