Hi!
> With it, the protocol in the client daemon will ack the kernel _before_
> it gets an ack from the remote server. That should help relieve the
> deadlock. Things then go like this:
>
> kernel runs low on memory
> kernel flushes buffers to device drivers under pressure
> nbd client daemon sends to the net
> * client acks kernel and releases buffers in kernel
> server on the _same machine_ receives request over the net
> server tries to write request to disk
> server process needs buffers to write to
> * server gets buffers released by client in kernel
>
> At least, potentially. If I recall right, there's still a deadlock
> window in-kernel, but it's small. I don't recall the details. Oh -
> well, the request still hangs around in the driver until the client
> daemon acks .. maybe the client daemon can't ack without being swapped
> in first, and that'd be deadlock.
>
> Well, there's a "-s" flag (for swap devices) that does an mlockall()
> that might take care of that. So "-a -s" might do it. Really needs
> a "-aa" option (release write request in kernel asap).
Well, with mlockall(), I'd believe it could be made to work. Okay.
Pavel
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This archive was generated by hypermail 2b29 : Tue Apr 23 2002 - 22:00:30 EST