[Dev] Setting dash as default shell (or getting rid of bash)

Barbieri, Gustavo gustavo.barbieri at intel.com
Tue Oct 1 19:13:59 GMT 2013


I was told that BTRFS was smart to not compress formats that are compressed already. Don’t know if this is a rollback if the compression rate is not good or if there is actually some matching in the file header.

--
Gustavo Sverzut Barbieri
Intel Open source Technology Center

From: Carsten Haitzler [mailto:c.haitzler at samsung.com]
Sent: Tuesday, October 01, 2013 12:14 AM
To: myungjoo.ham at samsung.com
Cc: Barbieri, Gustavo; dev at lists.tizen.org; 정재훈
Subject: Re: [Dev] Setting dash as default shell (or getting rid of bash)

i wonder how it figures if its "beneficial" :) hmm "if the first portion is not smaller"... this could be a problem with some file formats.. is this just "smaller" or "significantly smaller"? eg edj (eet) files have a header and directory block - its never compressed for speed of lookups, but each data segment in the file may (or may not be) compressed via any one of several compression methods (xlib, lz4/lz4hc, jpeg for lossy images etc.)... :) it'd be nice to be able to provide globs like "do not compress *.edj, *.jpg, *.png .... etc." :)

btw  lz4 or lz4hc might be an awesome addition to the compression algos supported. it seems to be "in progress". :)
On 10/01/2013 11:04 AM, MyungJoo Ham wrote:

With BTRFS you may "compress everything forcibly" or "compress if seems beneficial".

You may use "+c" to force compression on a file, but it seems that you cannot foce not to compress.

https://btrfs.wiki.kernel.org/index.php/Compression



Jaehoon (jh80.chung at samsung<mailto:jh80.chung at samsung>) may give more input; he has been experimenting with BTRFS & F2FS for Tizen 2.2.



------- Original Message -------

Sender : 하이츨러<c.haitzler at samsung.com><mailto:c.haitzler at samsung.com> 수석/차세대Computing Lab(S/W센터)/삼성전자

Date : 2013-10-01 10:51 (GMT+09:00)

Title : Re: [Dev] Setting dash as default shell (or getting rid of bash)


there is? cool. how do you enable compression? is it "compress everything by default" or can you "cmod" or chattr etc. specific files to then indicate to the fs to go compress them... ?
On 10/01/2013 06:20 AM, Barbieri, Gustavo wrote:
There is transparent decompression for btrfs including different methods such as lzo or zlib.
--
Gustavo Sverzut Barbieri
Intel Open source Technology Center
From: dev-bounces at lists.tizen.org<mailto:dev-bounces at lists.tizen.org> [mailto:dev-bounces at lists.tizen.org] On Behalf Of Carsten Haitzler
Sent: Sunday, September 29, 2013 11:50 PM
To: dev at lists.tizen.org<mailto:dev at lists.tizen.org>
Subject: Re: [Dev] Setting dash as default shell (or getting rid of bash)
On 09/28/2013 02:33 AM, Thiago Macieira wrote:

On sexta-feira, 27 de setembro de 2013 12:09:17, Leandro Pereira wrote:

If you're concerned about binary size, you could use a binary packer

such as UPX. A quick test here, compressing my own shell (on a x86-64

machine) yields pretty good compression. UPX decompresses really quickly

so it's very unlikely it'll become a bottleneck:



Binary compression is a trade-off between disk space usage and RAM usage.

Depending on the system, it might also be a security risk.



That's because the decompressor needs writable pages to decompress the image

to, then mark it as executable. Hopefully, the decompressor moves from RW to

RX instead of RWX, but you need to check that. And in any case, since those

pages aren't backed by actual files on disk, the kernel must use the swap if it

needs to discard the pages, even the unused pages.

if anything this would be best done with filesystem native compression (ala cramfs) and then the pages are at least backed and shared. :) short-term this only helps if we move to use cramfs, but longer-term it may be a valid "todo list" item to look at adding transparent decompression to btrfs/f2fs/ext4 etc.












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MyungJoo Ham (함명주), PHD
System S/W Lab, S/W Platform Team, Software Center
Samsung Electronics
Cell: +82-10-6714-2858





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