Large amounts of memory access operations cause panic under CURRENT (was "Large gap between fwrite and write, and fread and read")

[Milos Vyletel]

> Go figure it'd cause panics for other people.
> 
> I wasn't using zfs at all but it panicked anyhow once (my amd64 VM only, 
> not my i386 test server, surprisingly). I wish I'd gotten the panic but I 
> walked away to get a glass of water, and there wasn't a core dump because 
> the VM shut down completely instead of restarting. Heh.
> 
> My virtual machine died around 90k on the first trial though. I'll be sure 
> to reduce the amount and see what happens, and I'll put nanosleeps or 
> usleeps between the read and write ops to see if that alleviates the race 
> condition seen, but I'll keep the problem code around for reference later 
> in case I've stimulated some sort of weird bug in FreeBSD, or otherwise.
> 
> Both my VM and test server run almost no programs though other than samba 
> and rsync, so you'll probably see the panic faster / more frequently than I 
> will if you run a lot more programs resident in memory.
> 
> Just curious, what scheduler are you using on CURRENT, what processor do 
> you have, and what are your memory specs?
> 
> Thanks,
> -Garrett
> 

Hi Garrett,

this is just my desktop where is running only Xorg, fluxbox, few aterms and
firefox. But i can get the panic on console too, shortly after booting. I'm
using SCHED_ULE.

CPU: AMD Athlon(tm) 64 X2 Dual Core Processor 4200+ (2205.01-MHz K8-class CPU)
  Origin = "AuthenticAMD"  Id = 0x20f32  Stepping = 2
  Features=0x178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,MMX,FXSR,SSE,SSE2,HTT>
  Features2=0x1<SSE3>
  AMD Features=0xe2500800<SYSCALL,NX,MMX+,FFXSR,LM,3DNow!+,3DNow!>
  AMD Features2=0x3<LAHF,CMP>
  Cores per package: 2
usable memory = 3211718656 (3062 MB)
avail memory  = 3105570816 (2961 MB)

For the record, it crashes few times before it hit 100k iterations, before i put
debug printf in your code and increase MAX_ITERATIONS to 1m. And as far as I
can tell, I had pretty much the same results as you've measured.

mv