more weird bugs with mmap-ing via NFS

[Kostik Belousov]

On Tue, Mar 21, 2006 at 09:07:48PM -0500, Mikhail Teterin wrote:
> в?второк 21 березень 2006 20:53, Matthew Dillon Ви написали:
> >     Ah ha.  That's the problem.  I don't know why you are getting a write
> >     error, but that is preventing the client from cleaning out the dirty
> >     buffers. The number of dirty buffers continues to rise and the client
> >     is just cycling on them over and over trying to write them out,
> >     because it's just as confused about why it is getting a permission
> >     denied error as you are
> 
> Well, whatever it is, this means a big juicy bug, does not it? I mean, the 
> client should not get "confused" like this _ever_, but _especially_, when it 
> is talking to a fellow FreeBSD NFS-server.

AFAIU, this is the design issue with unix buffer cache. System
does assume that it can free dirty buffer (by writing it to the storage).
See my later answer on the "nfsaio" problem, where the similar issues
arise. Machine completely wedges if flushing of the dirty
buffers stalls.

I would be happy to be pointed out that my opinion is wrong, but fixing
that problem would require big amount of reachitecturing the system.
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