linux-ext4 - Re: [PATCH] ext4: ratelimit the file system mounted message

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Message-ID: <20150818035505.GZ17933@dhcp-13-216.nay.redhat.com>
Date:	Tue, 18 Aug 2015 11:55:05 +0800
From:	Eryu Guan <eguan@...hat.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	fstests@...r.kernel.org
Subject: Re: [PATCH] ext4: ratelimit the file system mounted message

On Tue, Aug 18, 2015 at 09:07:52AM +1000, Dave Chinner wrote:
> [cc fstests@...r.kernel.org as we are talking about the test rather
> than the kernel behaviour. ]
> 
[snip]
> > In all cases, ext3/305 reliably reproduced the failure within 30
> > mount/unmount cycles, and in most cases, under a dozen cycles.  (i.e.,
> > under two seconds, and usually in a fraction of a second).  So I'm not
> > entirely sure why the test was written to run the loop for 3 minutes
> > and thousands of mount/unmount cycles.
> 
> There were lots of tests being written at the time that used a 3
> minute timeout. It's another of those red flags that I tend to
> push back on these days, and this is an example of why - usually the
> problem can be hit very quickly, or the test is extremely unreliable
> and long runtime is the only way to trigger the race. Hence
> running for X minutes doesn't really prove anything....

IIRC, 3 minutes time limit was based on my testing before I submitted
the patch, but I could be wrong, it was two years ago..

I think I have better understanding of xfstests and regression tests
now than two years ago, after years education on the list (mainly by
Dave :-))

> 
> > Eryu, you wrote the test; any thoughts?  At the very least I'd suggest
> > cutting the test down so that it runs for at most 2 seconds, if for no
> > other reason than to speed up regression test runs.
> 
> Rather than time limiting, how about bounding the number of
> mount/unmount cycles?

Agreed, 30 cycles seem a reasonable number, I can prepare a patch if no
objection.

Thanks Ted and Dave for looking into this!

Eryu
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