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[PATCH 1/1] NBD: allow nbd to be used locally

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From: Paul Clements
Subject: [PATCH 1/1] NBD: allow nbd to be used locally
Date: Sunday, March 9, 2008 - 3:47 pm

This patch allows a Network Block Device to be mounted locally 
(nbd-client to nbd-server over 127.0.0.1).

It creates a kthread to avoid the deadlock described in NBD tools 
documentation. So, if nbd-client hangs waiting for pages, the kblockd 
thread can continue its work and free pages.

I have tested the patch to verify that it avoids the hang that occurs 
when writing to a localhost nbd connection. I have also tested to verify 
that no performance degradation results from the additional thread and 
queue.

Patch originally from Laurent Vivier.

Thanks,
Paul

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From: Pavel Machek
Subject: Re: [PATCH 1/1] NBD: allow nbd to be used locally
Date: Monday, March 10, 2008 - 3:29 am

What happens if your new kthread blocks on memory allocation?
									Pavel-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
--


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From: Paul Clements
Subject: Re: [PATCH 1/1] NBD: allow nbd to be used locally
Date: Monday, March 10, 2008 - 10:26 am

Well, we expect that. The reason for the new thread is so that it hangs, 
rather than kblockd hanging (which on a UP system brings all I/O to a 
halt). As long as kblockd can continue making progress, we eventually 
free up memory and then NBD can finish its requests, too.

--
Paul
--


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From: Pavel Machek
Subject: Re: [PATCH 1/1] NBD: allow nbd to be used locally
Date: Tuesday, March 11, 2008 - 3:09 am

...unless all the memory is in dirty buffers for nbd, and nbd server
is swapped out or something?
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
--


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From: Wouter Verhelst
Subject: Re: [Nbd] [PATCH 1/1] NBD: allow nbd to be used locally
Date: Monday, March 24, 2008 - 1:37 pm

Note that I'm not a kernel hacker, so might be terribly mistaken here...

but I feel I should point out that this patch solves the issue that no
two block devices can flush their dirty buffers at the same time.
Without this patch, you can't write to a _filesystem_ on an NBD device
if that's connected to a server on the localhost. You are correct that
this does not solve the deadlock in swapping to NBD devices, but that's
not the only existing deadlock issue in NBD to localhost...

-- 
<Lo-lan-do> Home is where you have to wash the dishes.
  -- #debian-devel, Freenode, 2004-09-22
--


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From: Pavel Machek
Subject: Re: [Nbd] [PATCH 1/1] NBD: allow nbd to be used locally
Date: Monday, March 24, 2008 - 2:58 pm

Same issue with swapping probably exists with dirty block
writeout... swapoff -a, and filesystem becomes very similar to swap.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
pomozte zachranit klanovicky les:  http://www.ujezdskystrom.info/
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Previous thread: [PATCH] signals: document CLD_CONTINUED notification mechanics by Oleg Nesterov on Sunday, March 9, 2008 - 2:53 pm. (4 messages)

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