linux-kernel - Re: xfs: does mkfs.xfs require fancy switches to get decent performance? (was Tux3 Report: How fast can we fsync?)

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Date:	Tue, 12 May 2015 00:12:23 +0200
From:	Pavel Machek <pavel@....cz>
To:	Daniel Phillips <daniel@...nq.net>
Cc:	Howard Chu <hyc@...as.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Dave Chinner <david@...morbit.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	tux3@...3.org, Theodore Ts'o <tytso@....edu>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: xfs: does mkfs.xfs require fancy switches to get decent
 performance? (was Tux3 Report: How fast can we fsync?)

Hi!

> > It is a fact of life that when you change one aspect of an intimately interconnected system,
> > something else will change as well. You have naive/nonexistent free space management now; when you
> > design something workable there it is going to impact everything else you've already done. It's an
> > easy bet that the impact will be negative, the only question is to what degree.
> 
> You might lose that bet. For example, suppose we do strictly linear allocation
> each delta, and just leave nice big gaps between the deltas for future
> expansion. Clearly, we run at similar or identical speed to the current naive
> strategy until we must start filling in the gaps, and at that point our layout
> is not any worse than XFS, which started bad and stayed that way.

Umm, are you sure. If "some areas of disk are faster than others" is
still true on todays harddrives, the gaps will decrease the
performance (as you'll "use up" the fast areas more quickly).

Anyway... you have brand new filesystem. Of course it should be
faster/better/nicer than the existing filesystems. So don't be too
harsh with XFS people.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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