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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 13 Mar 2024 14:51:38 -0700
Message-ID: <CAHk-=whbgtooUErM9bOP2iWimndpkPLaPy1YZmbmHACU07h3Mw@mail.gmail.com>
Subject: Re: [GIT PULL] bcachefs updates for 6.9
To: Kent Overstreet <kent.overstreet@linux.dev>
Cc: "Darrick J. Wong" <djwong@kernel.org>, linux-bcachefs@vger.kernel.org, 
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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On Wed, 13 Mar 2024 at 14:34, Kent Overstreet <kent.overstreet@linux.dev> wrote:
>
> I liked your MAD suggestion, but the catch was that we need an
> exponentially weighted version,

The code for the weighted version literally doesn't change.

The variance value is different, but the difference between MAD and
standard deviation is basically just a constant factor (which will be
different for different distributions, but so what? Any _particular_
case will have a particular distribution).

So why would a constant factor make _any_ difference for any
exponential weighting?

Anyway, feel free to keep your code in bcachefs.

And maybe xfs even wants to copy that code. I don't care, it seems
stupid, but that's a filesystem choice.

But if we're making it a generic kernel library, it needs to be sane.
Not making people do 64-bit square roots and 128-bit divides just for
a random statistical element.

              Linus