From: "Jörn Engel" <joern@wohnheim.fh-wedel.de>
To: David Woodhouse <dwmw2@infradead.org>
Cc: linux-mtd@lists.infradead.org
Cc: jffs-dev@axis.com
Cc: J B <mad_flasher@hotmail.com>
Subject: Re: jffs2 fragmentation
Date: Fri, 31 Oct 2003 12:24:21 +0100 [thread overview]
Message-ID: <20031031112421.GC5604@wohnheim.fh-wedel.de> (raw)
In-Reply-To: <1067539988.3423.208.camel@hades.cambridge.redhat.com>
On Thu, 30 October 2003 18:53:08 +0000, David Woodhouse wrote:
> On Sat, 2003-10-18 at 09:20 -0500, J B wrote:
> > Normally, a rm/cp pair takes about 2 minutes on my system. After about 10
> > iterations, the copies begin to take longer, about 3-4 minutes. After
> > about 10 iterations they take upwards of 1/2 an hour.
>
> I suspect you've triggered the worst case of a performance bug which
> I've known about for a while.
>
> We should write new data out to one empty block, while writing out
> garbage-collected data out to another. We don't do that at the moment;
> we interleave old and new data and then you erase your new file, leaving
> us with a very suboptimal mix of valid and obsolete nodes in each
> eraseblock we've been writing to.
>
> I'm still a bit surprised it takes half an hour though.
If your explanation is correct, a shift from 4 to 28 minutes would
correspond to 6 clean nodes reused for every 1 dirty node deleted and
new node written.
Doesn't make a lot of sense with a filesystem that should be >80% free
or dirty, does it?
Jörn
--
Fools ignore complexity. Pragmatists suffer it.
Some can avoid it. Geniuses remove it.
-- Perlis's Programming Proverb #58, SIGPLAN Notices, Sept. 1982
next prev parent reply other threads:[~2003-10-31 11:26 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-18 14:20 jffs2 fragmentation J B
2003-10-30 17:45 ` Jörn Engel
2003-10-30 18:53 ` David Woodhouse
2003-10-31 11:24 ` Jörn Engel [this message]
2003-10-31 11:53 ` David Woodhouse
2003-10-31 12:50 ` Jörn Engel
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