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

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Message-ID: <5553CB10.70407@phunq.net>
Date:	Wed, 13 May 2015 15:07:12 -0700
From:	Daniel Phillips <daniel@...nq.net>
To:	linux-kernel@...r.kernel.org
CC:	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: Tux3 Report: How fast can we fail?

Addendum to that post...

On 05/12/2015 10:46 AM, I wrote:
> ...For example, we currently
> overestimate the cost of a rewrite because we would need to go poking
> around in btrees to do that more accurately. Fixing that will be quite
> a bit of work...

Ah no, I was wrong about that, it will not be a lot of work because
it does not need to be done.

Charging the full cost of a rewrite as if it is a new write is the
right thing to do because we need to be sure the commit can allocate
space to redirect the existing blocks before it frees the old ones.
So that means there is no need for the front end to go delving into
file metadata, ever, which is a relief because that would have been
expensive and messy.

Regards,

Daniel
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