NFS client/buffer cache deadlock

[Marc Olzheim]

[changed cc: from standards@ back to stable@ again.]

On Tue, Apr 26, 2005 at 12:25:49PM -0400, Brian Fundakowski Feldman wrote:
> You can assure that this happens in only two ways:
> 
> 1. Make a complete copy of the data.  This is what currently occurs:
>    it gets stuffed into the buffer cache as the write happens.
> 2. Keep the data around synchronously -- by virtue of the write system
>    call being used synchronously, the thread's VM context is around,
>    and duplication need not occur.

It seems as though FreeBSD 4.x either used 2) or does something wrong
indeed. Why would 2) be a problem on FreeBSD 5.x ? Can't the pages
written from be locked during the write, instead of copied internally ?

Btw. running the writev program with 20 * 100 MB on UFS on a 512MB
FreeBSD 6-CURRENT system practicly locks the filesystem down _and_
causes all processes to be swapped out in favor of the buffer cache.
'top' however, doesnt' show a rise in BUF usage.

On FreeBSD 4.x, the system performance as usual during the writev to
UFS.

Marc
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