linux-kernel - Re: [PATCH 1/1] NBD: allow nbd to be used locally

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Message-ID: <47D56F4A.5070208@steeleye.com>
Date:	Mon, 10 Mar 2008 13:26:34 -0400
From:	Paul Clements <paul.clements@...eleye.com>
To:	Pavel Machek <pavel@....cz>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, nbd-general@...ts.sourceforge.net,
	Laurent Vivier <Laurent.Vivier@...l.net>
Subject: Re: [PATCH 1/1] NBD: allow nbd to be used locally

Pavel Machek wrote:

>> 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.
> 
> What happens if your new kthread blocks on memory allocation?

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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