On Mar 30, 2021, at 4:50 AM, Oleksandr Natalenko [off-list ref] wrote:

On Tue, Mar 30, 2021 at 01:32:35PM +0200, Piotr Gorski wrote:

quoted

kmod 28 supports modules compressed in zstd format so let's add this possibility to kernel.

Signed-off-by: Piotr Gorski <redacted>
---
Makefile     | 7 +++++--
init/Kconfig | 9 ++++++---
2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index 5160ff8903c1..82f4f4cc2955 100644
--- a/Makefile
+++ b/Makefile

@@ -1156,8 +1156,8 @@ endif # INSTALL_MOD_STRIP

export mod_strip_cmd

# CONFIG_MODULE_COMPRESS, if defined, will cause module to be compressed
-# after they are installed in agreement with CONFIG_MODULE_COMPRESS_GZIP
-# or CONFIG_MODULE_COMPRESS_XZ.
+# after they are installed in agreement with CONFIG_MODULE_COMPRESS_GZIP,
+# CONFIG_MODULE_COMPRESS_XZ, or CONFIG_MODULE_COMPRESS_ZSTD.

mod_compress_cmd = true
ifdef CONFIG_MODULE_COMPRESS

@@ -1167,6 +1167,9 @@ ifdef CONFIG_MODULE_COMPRESS
  ifdef CONFIG_MODULE_COMPRESS_XZ
    mod_compress_cmd = $(XZ) --lzma2=dict=2MiB -f
  endif # CONFIG_MODULE_COMPRESS_XZ
+  ifdef CONFIG_MODULE_COMPRESS_ZSTD
+    mod_compress_cmd = $(ZSTD) -T0 --rm -f -q

This will use the default zstd level, level 3. I think it would make more sense to use a high
compression level. Level 19 would probably be a good choice. That will choose a window
size of up to 8MB, meaning the decompressor needs to allocate that much memory. If that
is unacceptable, you could use `zstd -T0 --rm -f -q -19 --zstd=wlog=21`, which will use a
window size of up to 2MB, to match the XZ command. Note that if the file is smaller than
the window size, it will be shrunk to the smallest power of two at least as large as the file.

Best,
Nick Terrell

quoted

+  endif # CONFIG_MODULE_COMPRESS_ZSTD
endif # CONFIG_MODULE_COMPRESS
export mod_compress_cmd

diff --git a/init/Kconfig b/init/Kconfig
index 8c2cfd88f6ef..86a452bc2747 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -2250,8 +2250,8 @@ config MODULE_COMPRESS

	bool "Compress modules on installation"
	help

-	  Compresses kernel modules when 'make modules_install' is run; gzip or
-	  xz depending on "Compression algorithm" below.
+	  Compresses kernel modules when 'make modules_install' is run; gzip,
+	  xz, or zstd depending on "Compression algorithm" below.

	  module-init-tools MAY support gzip, and kmod MAY support gzip and xz.

@@ -2273,7 +2273,7 @@ choice

	  This determines which sort of compression will be used during
	  'make modules_install'.

-	  GZIP (default) and XZ are supported.
+	  GZIP (default), XZ, and ZSTD are supported.

config MODULE_COMPRESS_GZIP
	bool "GZIP"

@@ -2281,6 +2281,9 @@ config MODULE_COMPRESS_GZIP

config MODULE_COMPRESS_XZ
	bool "XZ"

+config MODULE_COMPRESS_ZSTD
+	bool "ZSTD"
+
endchoice

config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
-- 
2.31.0.97.g1424303384

Great!

Reviewed-by: Oleksandr Natalenko <redacted>

This works perfectly fine in Arch Linux if accompanied by the
following mkinitcpio amendment: [1].

I'm also Cc'ing other people from get_maintainers output just
to make this submission more visible.

Thanks.

[1] https://github.com/archlinux/mkinitcpio/pull/43

-- 
 Oleksandr Natalenko (post-factum)