Hi,
I'm running a server that has 1500+ mounted local filesystems.
All of these local filesystems are exported through NFS by this server.
When an NFS-client tries to access one of these exported filesystems,
for example doing a simple 'ls' in a mounted NFS, rpc.mountd on the
server takes 100% CPU and starts to spin over reading /etc/mtab which is
linked to /proc/mounts and totals to about 200KB in size. The client
stalls all the while rpc.mountd is busy reading /etc/mtab for every
filesystem mounted, and then some more.
I made a strace of rpc.mountd during such a run to gather some stats:
# cut -d'(' -f1 straceout.25103 | sort | uniq -c | sort -n
3 fadvise64
6 ioctl
11 lseek
33 readlink
43 select
53 write
809 statfs
814 lstat
1282 stat
17043 mmap
17043 munmap
17088 fstat
17895 open
21728 openat
37295 close
40352 getdents
458616 newfstatat
3763233 read
# grep -c "open.*mtab" straceout.25103
17028
This entire process of reading /etc/mtab 17028 times takes a lot of time
during which the client stalls, but in the end 'it just works fine'.
It just takes ages when you try to tab-complete on a client.
What would be needed to debug and optimise this?
Could someone point me to the code that is involved in doing this?
I'm not a good C-coder but perhaps i can debug more...
Any insights appreciated!
With regards,
-Sander.
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