more weird bugs with mmap-ing via NFS

Mikhail Teterin mi+mx at
Wed Mar 22 18:13:22 UTC 2006

середа 22 березень 2006 12:23, Matthew Dillon Ви написали:
>     My guess is that you are exporting the filesystem as a particular
>     user id that is not root (i.e. you do not have -maproot=root: in the
>     exports line on the server).

Yes, indeed, re-exporting with -maproot=0 leads to normal behavior. Thanks for 
the workaround!

Here are the stats: As the program is working hard, the incoming traffic on 
the client is about 200Kb/s (I guess, all those not yet existant pages being 
faulted in) and the outgoing -- about 7Kb/s with occasional spikes to 8Mb/s 
(I guess, this is when the flushing takes place).

>     What is likely happening is that the NFS client is trying to push out
>     the pages using the root uid rather then the user uid.  This is a
>     highly probable circumstance for VM pages because once they get
>     disassociated from the related buffer cache buffer, the cred information
>     for the last process to modify the related VM pages is lost.  When the
>     kernel tries to flush the pages out it winds up using root creds.

So mmap is just a more "reliable" way to trigger this problem, right?

Is not this, like, a major bug? A file can be opened, written to for a while, 
and then -- at a semi-random moment -- the log will drop across the road? 

Thanks a lot to all concerned for helping solve this problem. Yours,


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