[OpenAFS] kernel crash linux-4.4.15 openafs-1.6.18.2

[Hans-Werner Paulsen]

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Dear All,
10 days ago I have reported a problem with OpenAFS on Linux to=20
openafs-bugs (#133467). Now I have found more results and a solution to=20
circumvent this problem.
I have a simple program executing the following calls again and again:
   fopen afs-file mode append
   fwrite 64MiB
   fclose
The machine has a disk cache with 16GiB and afsd is started with
   -afsdb -blocks 14862564 -stat 65536 -volumes 128 -chunksize 18
The first 40 64MiB writes took about 0.7s each, then the time to
append 64MiB is 1.2s for block #41 and is growing to 11s for write #154, =

then I run a "fs flushall" and the write time drops to 0.8s, but is=20
growing again. When I kill the process, I get a kernel crash most of the =

time.

When I use afsd -dcache 32768, I see the following: for the first 128=20
writes (=3D128*64MiB=3D32768*chunksize) the time for each write is growin=
g=20
from 0.7s to 1.5s, then it jumps to 6.5s and is growing to ~10s for=20
write #154 and ~19s for write #220

For our production machines I have set the chunksize to 2^21 and use the =

default dcache size (10000?). Now we do not see any problems with our=20
current jobs.

It seems that the algorithm to look for free dcache entries is very=20
slow. Any hints?

Best regards,
Hans-Werner


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