linux-kernel - Re: [PATCH 0/2] Squashfs: add LZ4 compression

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Message-ID: <alpine.DEB.2.10.1411271716300.17270@biff2>
Date:	Thu, 27 Nov 2014 17:55:40 +0100 (CET)
From:	Martin Vath <martin@...th.de>
To:	Marcin Szychowski <szycha@...il.com>
cc:	Bruno Wolff III <bruno@...ff.to>,
	Phillip Lougher <phillip@...ashfs.org.uk>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	texstar@...il.com, Martin Vaeth <martin@...th.de>,
	guanx.bac@...il.com, dave@...ilevsky.ca,
	blyons@...dents.naropa.edu, tokiclover@...il.com, afm404@...il.com,
	hugochevrain@...il.com
Subject: Re: [PATCH 0/2] Squashfs: add LZ4 compression

Hi:

> squashfs+lz4 / aufs to speed up my laptop

Squashfs proves its usefulness especially in combination
with aufs or overlayfs; I suppose that this combination
will become more popular with the spreading of overlayfs
(e.g. to save disk space etc.)

For users with such a combination, it is especially important
to get a fast (re)compression of huge directories.

The speed of LZ4 for compression in such a setting is really incredible.
Just for orientation for myself, I made a list of times/sizes
on some machines I had access to:

https://github.com/vaeth/squashmount/blob/master/compress.txt

(I do not claim that this is a scientific benchmark - just a
straightforward average over several runs).
The results for the kernel source and libreoffice are really
unbelievable, but I repeated them several times (and,
as you can see, for the kernel sources on different machines).

>From the user perspective, it is mainly important that
the files compressed in this way can be read by the kernel -
the decompression speed is here secondary, so I made no comparison
for this case, although lz4 is known to be very fast also
for decompression.

I would really like to see lz4 support included in the
squashfs kernel driver. I cannot imagine any negative consequences,
especially since squashfs and lz4 are in the kernel, anyway.

Sincerely
Martin Väth