Bug#976054: initramfs-tools: [RFC] Compress initramfs file with zstd
Package: initramfs-tools
Version: 0.139
Severity: normal
Tags: patch
Dear Maintainer,
Now initramfs files are compressed with gzip
But we can use other compression, i.e. LZO, LZ4 and ZSTD.
Then which one is the best?
* compression ratio
ZSTD > GZIP > LZO > LZ4
* decompression speed
LZ4 > LZO = ZSTD > GZIP
I suggest to choose ZSTD, instead of GZIP since
- better compression ratio than current GZIP
- also better decompresion speed than current GZIP
------------------------------------------------------------------------------
With gzip
------------------------------------------------------------------------------
$ file /boot/initrd.img-5.9.0-*
/boot/initrd.img-5.9.0-3-amd64: gzip compressed data, from Unix, original size modulo 2^32 197680640
/boot/initrd.img-5.9.0-4-amd64: gzip compressed data, from Unix, original size modulo 2^32 197594112
$ du -h /boot/initrd.img-5.9.0-*
59M /boot/initrd.img-5.9.0-3-amd64
59M /boot/initrd.img-5.9.0-4-amd64
------------------------------------------------------------------------------
With zstd
------------------------------------------------------------------------------
$ file /boot/initrd.img-5.9.0-*
/boot/initrd.img-5.9.0-3-amd64: Zstandard compressed data (v0.8+), Dictionary ID: None
/boot/initrd.img-5.9.0-4-amd64: Zstandard compressed data (v0.8+), Dictionary ID: None
$ du -h /boot/initrd.img-5.9.0-*
40M /boot/initrd.img-5.9.0-3-amd64
40M /boot/initrd.img-5.9.0-4-amd64
------------------------------------------------------------------------------
Yes, 59MB initramfs file becomes 40MB (2/3)! plus bonus, better decompression speed.
However, there's a problem to do so - zstd package's Priority is not standard one
- it's "optional".
> Package: gzip
> Version: 1.10-2
> Priority: required
> Package: zstd
> Version: 1.4.5+dfsg-4
> Priority: optional
It means there is not zstd package in every environment. And, just raise its Priority
means bloat minimal system size that is a problem we want to avoid.
Now initramfs-tools has a hack to avoid zstd (and other compression tools)
absence in mkinitramfs command.
> if ! command -v "${compress}" >/dev/null 2>&1; then
> compress=gzip
> echo "No ${compress} in ${PATH}, using gzip"
> fi
Set COMPRESS=zstd in /etc/initramfs/initramfs.conf and no zstd installed,
there's no problem.
> $ sudo update-initramfs -u
> update-initramfs: Generating /boot/initrd.img-5.9.0-4-amd64
> No zstd in /usr/bin:/sbin:/bin, using gzip
(abobe message is patched with #971270)
So, just set default compression as zstd can brings better result for many users,
IMO (Not sure raising zstd package Priority (to standard) is required or not).
>From 78c4fe32a447b0dc46045f0c8a32a4b246691711 Mon Sep 17 00:00:00 2001
From: Hideki Yamane <henrich@debian.org>
Date: Sun, 29 Nov 2020 10:05:48 +0900
Subject: [PATCH] Use zstd as default compression for initramfs
---
conf/initramfs.conf | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/conf/initramfs.conf b/conf/initramfs.conf
index 01bdd85..a0c051b 100644
--- a/conf/initramfs.conf
+++ b/conf/initramfs.conf
@@ -41,7 +41,7 @@ KEYMAP=n
# COMPRESS: [ gzip | bzip2 | lz4 | lzma | lzop | xz | zstd ]
#
-COMPRESS=gzip
+COMPRESS=zstd
#
# DEVICE: ...
--
2.29.2
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