linux-ext4 - Re: [RFC PATCH 1/1] ext4: Try to better reuse recently freed space

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Message-ID: <20140401144708.GT4911@thunk.org>
Date:	Tue, 1 Apr 2014 10:47:08 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	Lukáš Czerner <lczerner@...hat.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] ext4: Try to better reuse recently freed space

On Tue, Apr 01, 2014 at 03:44:53PM +0400, Dmitry Monakhov wrote:
> BTW where this can I find this discussion? I would like to cooperate
> this that activity. Please CC me next time you will disscuss allocation
> performance mesurments. At Parallels we run https://oss.oracle.com/~mason/compilebench/
> as load simulator.

The discussion happened at the Ext4 developer's get together in Napa,
California, colocated with the LSF/MM and the Collaboration Summit.
You should go next year; it was a huge amount of fun, and there were a
bunch of other Parallels people there who can tell you about the
reception at the Jacuzzi Family Winery, etc.  :-)

I suspect there will be some future conversations at our weekly
conference calls.  Typically design stuff will happen there, but
technical low-level details about things like patches will happen on
the mailing list, so you'll be alerted when we start having specific
patches to evaluate and as we start putting together a set of
allocation benchmarks.

If you are interested in participating on the conference calls,
contact me off-line.  If the current time (8AM US/Pacific ; 11 AM
US/Eastern) isn't good for you, we can try to see if another time
works for everyone.

One of the discussion points that came up last week is that it would
be good if we can come up with allocation tests that are fast to run.
That might mean (for example) taking a workload such as compilebench,
and changing it to use fallocate() or having a mount option which
causes the actual data path writes to be skipped for files.  We would
then need to have some kind of metric to evaluate how "good" a
particular file system layout ends up being at the end of the
workload.  Not just for a specific file, but for all of the files in
some kind of holistic measurement of "goodness", as well as looking at
how fragmented the free space ended up being.  Exactly how we do this
is still something that we need to figure out; if you have any
suggestions, they would be most welcome!

Cheers,

					- Ted
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