linux-ext4 - Re: [PATCH v2] ext4: dynamical adjust the length of zero-out chunk

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Message-ID: <20120813184053.GE32484@thunk.org>
Date:	Mon, 13 Aug 2012 14:40:53 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Zach Brown <zab@...hat.com>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	Zheng Liu <wenqing.lz@...bao.com>,
	Eric Sandeen <sandeen@...hat.com>,
	Zheng Liu <gnehzuil.liu@...il.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] ext4: dynamical adjust the length of zero-out chunk

On Mon, Aug 13, 2012 at 10:32:24AM -0700, Zach Brown wrote:
> >     we allow it to be tunable via sysfs and set an initial default value
> >     of 32, so instead of creating uninitalized extents smaller than
> 
> s/32/16/?

Oops, nice catch.

> It'd be nice to define the tunable in terms of some fixed unit, kb or
> mb, whatever, and then translate to the block size in the code so people
> don't have to do that math by hand.
> 
> No?

Agreed, thanks for the suggestion.  The next question is whether the
default maximum zero-out size should be 256k (as previously
documented) or 128k (as previously coded).

The previously rule of thumb which I had used was that after doing a
random seek, the time needed to write 4k and 32k was pretty much in
the noise.  But that was a number from several years ago.  I suppose I
should do some quick experiments to see what is a good number these
days....

						- Ted
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