Date: Fri, 5 Feb 1999 11:47:05 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: current@FreeBSD.ORG Subject: Seeing NFS saturation 'loop' when installworld'ing to NFS / and /usr Message-ID: <199902051947.LAA98698@apollo.backplane.com>
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This is very odd. This is the approximate backtrace that I get
when I throw my test machine into DDB:
--- interrupt, ...
nfs_* routines....
cluster_wbuild
vfs_bio_awrite
flushdirtybuffers
bdwrite
nfs_write
vn_write
write
syscall
What is happening is that I am doing a 'make installworld' on my
test machine with / and /usr NFS V3 mounted R+W.
The install goes well, but four times so far an 'install' command has
gotten 'stuck' in 'R'un state and the network has gone into saturation.
It seems to be repreating the same NFS I/O over the network over and
over again as far as I can tell. It is very odd.
The network stays in saturation ( at 8 MBytes/sec ) until I kill -STOP
the install. It usually takes about a minute for the kill -STOP to take
effect ( which is also very odd ). If I then kill -CONT the install
program, the install resumes normally, finishes its write(), and
continues on normally.
The system is not locked up when this situation occurs.
As far as I can tell, it is some sort of weird interaction with the
flushdirtybuffers() routine and cluster_wbuild(), but I haven't a clue
as to what is causing the problem.
Sometimes when I break into DDB and do a backtrace, flushdirtybuffers()
is being called from a non-NFS element such as ffs_update(), so the
sequence looks like:
nfs_* routines....
cluster_wbuild
vfs_bio_awrite
flushdirtybuffers
bdwrite ( I think )
ffs_update
It is very odd. I don't suppose very many people try to make install
over NFS ( it works, you just have to chflags -R noschg the destination
on the NFS server before you run make install on the NFS client ).
-Matt
Matthew Dillon
<dillon@backplane.com>
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