linux-kernel - Re: Swap on loop device on tmpfs locks up machine

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Message-ID: <19f34abd0809271130h47cef59em759910b1cd2c920c@mail.gmail.com>
Date:	Sat, 27 Sep 2008 20:30:16 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Bill Davidsen" <davidsen@....com>
Cc:	"David Newall" <davidn@...idnewall.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Swap on loop device on tmpfs locks up machine

On Sat, Sep 27, 2008 at 7:38 PM, Bill Davidsen <davidsen@....com> wrote:
> David Newall wrote:
>>
>> Vegard Nossum wrote:
>>>
>>> It turns out that swap over loop device on tmpfs will lock up the
>>> machine.
>>
>> Doesn't tmpfs use otherwise-free virtual memory?  I expect the machine
>> would lock up if you put swap (i.e. additional virtual memory) on such a
>> device.
>
> To reinstate the paragraph from the O.P. you snipped:
>>> I'm not sure it's really a very good idea to do this in the first
>>> place, but should something give a warning or prevent a user from
>>> doing it?
>
> I think you are both right, it is a bad thing to do, it does seem to lock
> up, and something should prevent a user from doing that. But it may be
> easier to fix the lockup than get the "prevent" right, there appears to be a
> loop there.
>
> Just a simple questions to the O.P.: what were you thinking?!! Or was this a
> test just to see what would happen?

Just playing with the kernel :-)

Sometimes the "insane" things to do will turn up real errors in the
code. This one is in the borderlands, but I thought it wouldn't hurt
to post the results in either case.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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