linux-kernel - Re: Tux3 Report: How fast can we fail?

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Date:	Wed, 27 May 2015 17:21:24 +0200
From:	Mosis Tembo <mosis.tembo@...il.com>
To:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Tux3 Report: How fast can we fail?


On 05/27/2015 04:04 PM, Austin S Hemmelgarn wrote:
> On 2015-05-27 03:37, Mosis Tembo wrote:
>>
>> On 05/26/2015 12:03 PM, Pavel Machek wrote:
>>>> We identified the following quality metrics for this algorithm:
>>>>
>>>>   1) Never fails to detect out of space in the front end.
>>>>   2) Always fills a volume to 100% before reporting out of space.
>>>>   3) Allows rm, rmdir and truncate even when a volume is full.
>>
>> This is definitely nonsense. You can not rm, rmdir and truncate
>> when the volume is full. You will need a free space on disk to perform
>> such operations. Do you know why?
>>
> I assume you are referring either to Tux3 specifically or COW 
> filesystems in general,


I am referring to modern file systems with transaction models and 
delayed actions.
Tux3 is not the case?


> because you very much _can_ do any of those on any of the non-COW 
> filesystems in the Linux kernel


It is simply incorrect. ReiserFS is a counterexample.


> (I know from experience).  Also, IIRC, it was mentioned somewhere that 
> Tux3 keeps a small reserve of space on the volume for internal 
> operations; and, I would assume that if that is the case, it reports 
> the volume full when everything *except* that reserve of space is 
> used, in which case rm, rmdir, and truncate should work fine when the 
> volume is full.


Sorry, I prefer to not manipulate with rumors and assumptions when it comes
to the review for kernel inclusion.

Thanks,
M.T.

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