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Commit db2aa7fd authored by Francisco Blas Izquierdo Riera (klondike)'s avatar Francisco Blas Izquierdo Riera (klondike) Committed by Linus Torvalds
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initramfs: allow again choice of the embedded initram compression algorithm 

Choosing the appropriate compression option when using an embedded
initramfs can result in significant size differences in the resulting
data.

This is caused by avoiding double compression of the initramfs contents.
For example on my tests, choosing CONFIG_INITRAMFS_COMPRESSION_NONE when
compressing the kernel using XZ) results in up to 500KiB differences
(9MiB to 8.5MiB) in the kernel size as the dictionary will not get
polluted with uncomprensible data and may reuse kernel data too.

Despite embedding an uncompressed initramfs, a user may want to allow
for a compressed extra initramfs to be passed using the rd system, for
example to boot a recovery system.  9ba4bcb6 ("initramfs: read
CONFIG_RD_ variables for initramfs compression") broke that behavior by
making the choice based on CONFIG_RD_* instead of adding
CONFIG_INITRAMFS_COMPRESSION_LZ4.  Saddly, CONFIG_RD_* is also used to
choose the supported RD compression algorithms by the kernel and a user
may want to support more than one.

This patch also reverts commit 3e4e0f0a ("initramfs: remove
"compression mode" choice") restoring back the "compression mode" choice
and includes the CONFIG_INITRAMFS_COMPRESSION_LZ4 option which was never
added.

As a result the following options are added or readed affecting the embedded
initramfs compression:
  INITRAMFS_COMPRESSION_NONE Do no compression
  INITRAMFS_COMPRESSION_GZIP Compress using gzip
  INITRAMFS_COMPRESSION_BZIP2 Compress using bzip2
  INITRAMFS_COMPRESSION_LZMA Compress using lzma
  INITRAMFS_COMPRESSION_XZ Compress using xz
  INITRAMFS_COMPRESSION_LZO Compress using lzo
  INITRAMFS_COMPRESSION_LZ4 Compress using lz4

These depend on the corresponding CONFIG_RD_* option being set (except
NONE which has no dependencies).

This patch depends on the previous one (the previous version didn't) to
simplify the way in which the algorithm is chosen and keep backwards
compatibility with the behaviour introduced by 9ba4bcb6
("initramfs: read CONFIG_RD_ variables for initramfs compression").

Link: http://lkml.kernel.org/r/57EAD77B.7090607@klondike.es


Signed-off-by: default avatarFrancisco Blas Izquierdo Riera (klondike) <klondike@klondike.es>
Cc: P J P <ppandit@redhat.com>
Cc: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 35e669e1

usr/Kconfig

+117 −0
Original line number Diff line number Diff line
@@ -99,8 +99,125 @@ config RD_LZ4 
	  Support loading of a LZ4 encoded initial ramdisk or cpio buffer

	  If unsure, say N.



choice

	prompt "Built-in initramfs compression mode"

	depends on INITRAMFS_SOURCE!=""

	optional

	help

	  This option allows you to decide by which algorithm the builtin

	  initramfs will be compressed.  Several compression algorithms are

	  available, which differ in efficiency, compression and

	  decompression speed.  Compression speed is only relevant

	  when building a kernel.  Decompression speed is relevant at

	  each boot. Also the memory usage during decompression may become

	  relevant on memory constrained systems. This is usually based on the

	  dictionary size of the algorithm with algorithms like XZ and LZMA

	  featuring large dictionary sizes.



	  High compression options are mostly useful for users who are

	  low on RAM, since it reduces the memory consumption during

	  boot.



	  Keep in mind that your build system needs to provide the appropriate

	  compression tool to compress the generated initram cpio file for

	  embedding.



	  If in doubt, select 'None'



config INITRAMFS_COMPRESSION_NONE

	bool "None"

	help

	  Do not compress the built-in initramfs at all. This may sound wasteful

	  in space, but, you should be aware that the built-in initramfs will be

	  compressed at a later stage anyways along with the rest of the kernel,

	  on those architectures that support this. However, not compressing the

	  initramfs may lead to slightly higher memory consumption during a

	  short time at boot, while both the cpio image and the unpacked

	  filesystem image will be present in memory simultaneously



config INITRAMFS_COMPRESSION_GZIP

	bool "Gzip"

	depends on RD_GZIP

	help

	  Use the old and well tested gzip compression algorithm. Gzip provides

	  a good balance between compression ratio and decompression speed and

	  has a reasonable compression speed. It is also more likely to be

	  supported by your build system as the gzip tool is present by default

	  on most distros.



config INITRAMFS_COMPRESSION_BZIP2

	bool "Bzip2"

	depends on RD_BZIP2

	help

	  It's compression ratio and speed is intermediate. Decompression speed

	  is slowest among the choices. The initramfs size is about 10% smaller

	  with bzip2, in comparison to gzip. Bzip2 uses a large amount of

	  memory. For modern kernels you will need at least 8MB RAM or more for

	  booting.



	  If you choose this, keep in mind that you need to have the bzip2 tool

	  available to be able to compress the initram.



config INITRAMFS_COMPRESSION_LZMA

	bool "LZMA"

	depends on RD_LZMA

	help

	  This algorithm's compression ratio is best but has a large dictionary

	  size which might cause issues in memory constrained systems.

	  Decompression speed is between the other choices. Compression is

	  slowest. The initramfs size is about 33% smaller with LZMA in

	  comparison to gzip.



	  If you choose this, keep in mind that you may need to install the xz

	  or lzma tools to be able to compress the initram.



config INITRAMFS_COMPRESSION_XZ

	bool "XZ"

	depends on RD_XZ

	help

	  XZ uses the LZMA2 algorithm and has a large dictionary which may cause

	  problems on memory constrained systems. The initramfs size is about

	  30% smaller with XZ in comparison to gzip. Decompression speed is

	  better than that of bzip2 but worse than gzip and LZO. Compression is

	  slow.



	  If you choose this, keep in mind that you may need to install the xz

	  tool to be able to compress the initram.



config INITRAMFS_COMPRESSION_LZO

	bool "LZO"

	depends on RD_LZO

	help

	  It's compression ratio is the second poorest amongst the choices. The

	  kernel size is about 10% bigger than gzip. Despite that, it's

	  decompression speed is the second fastest and it's compression speed

	  is quite fast too.



	  If you choose this, keep in mind that you may need to install the lzop

	  tool to be able to compress the initram.



config INITRAMFS_COMPRESSION_LZ4

	bool "LZ4"

	depends on RD_LZ4

	help

	  It's compression ratio is the poorest amongst the choices. The kernel

	  size is about 15% bigger than gzip; however its decompression speed

	  is the fastest.



	  If you choose this, keep in mind that most distros don't provide lz4

	  by default which could cause a build failure.



endchoice



config INITRAMFS_COMPRESSION

	string

	default ""      if INITRAMFS_COMPRESSION_NONE

	default ".gz"   if INITRAMFS_COMPRESSION_GZIP

	default ".bz2"  if INITRAMFS_COMPRESSION_BZIP2

	default ".lzma" if INITRAMFS_COMPRESSION_LZMA

	default ".xz"   if INITRAMFS_COMPRESSION_XZ

	default ".lzo"  if INITRAMFS_COMPRESSION_LZO

	default ".lz4"  if INITRAMFS_COMPRESSION_LZ4

	default ".gz"   if RD_GZIP

	default ".lz4"  if RD_LZ4

	default ".lzo"  if RD_LZO