Re: [PATCH v4 0/8] Add support for ZSTD-compressed kernel and initramfs

[Gabriel C]

On 01.04.20 07:39, Nick Terrell wrote:
> From: Nick Terrell <terrelln@xxxxxx>
>
> Hi all,


Hi Nick,


> This patch set adds support for a ZSTD-compressed kernel, ramdisk, and
> initramfs in the kernel boot process. ZSTD-compressed ramdisk and initramfs
> are supported on all architectures. The ZSTD-compressed kernel is only
> hooked up to x86 in this patch set.
>
> Zstandard requires slightly more memory during the kernel decompression
> on x86 (192 KB vs 64 KB), and the memory usage is independent of the
> window size.
>
> Zstandard requires memory proprortional to the window size used during
> compression for decompressing the ramdisk image, since streaming mode is
> used. Newer versions of zstd (1.3.2+) list the window size of a file
> with `zstd -lv <file>'. The absolute maximum amount of memory required
> is just over 8 MB, but it can be controlled at compression time.
>
> This patch set has been boot tested with buildroot and QEMU based off
> of linux-5.6-rc6.
>
> On i386 and x86_64 I have tested the following configurations:
> * zstd compressed kernel and a separate zstd compressed initramfs
> * zstd compressed kernel and a built-in zstd compressed initramfs
> * gzip compressed kernel and a separate gzip compressed initramfs
> * gzip compressed kernel and a built-in gzip compressed initramfs


I tested this and already v2 and v3 on some boxes without a problem.


Also I've tested :

XZ compressed kernel ZSTD compressed initramfs ( XZ compressed modules )

XZ compressed kernel ZSTD compressed initramfs ( ZSTD compressed modules 
, that need an kmod patch )

ZSTD compressed kernel ZSTD compressed initramfs ( ZSTD compressed 
modules, that need an kmod patch )

ZSTD compressed kernel XZ compressed initramfs ( ZSTD/XZ compressed 
modules )


> On arm and aarch64 I tested the same configurations, except that the kernel is
> always gzip compressed.
>
> Facebook has been using v1 of these patches on x86_64 devices for more than 6
> months. When we switched from a xz compressed initramfs to a zstd compressed
> initramfs decompression time shrunk from 12 seconds to 3 seconds. When we
> switched from a xz compressed kernel to a zstd compressed kernel we saved 2
> seconds of boot time.


I can confirm that on my server I tested the patches decompression went 
down

6 secs and 3.1 seconds faster boot time with zstd compressed kernel.


Also I see around 2++seconds faster boot across all testing boxes.


> Facebook has been using v2 of these patches on aarch64 devices for a few weeks.
> When we switched from an lzma compressed initramfs to a zstd compressed initramfs
> decompression time shrunk from 27 seconds to 8 seconds.
>
> The zstd compressed kernel is smaller than the gzip compressed kernel but larger
> than the xz or lzma compressed kernels, and it decompresses faster than
> everything except lz4. See the table below for the measurement of an x86_64
> kernel ordered by compressed size:
>
> algo	size
> xz  	 6,509,792
> lzma	 6,856,576
> zstd	 7,399,157
> gzip	 8,522,527
> bzip	 8,629,603
> lzo 	 9,808,035
> lz4 	10,705,570
> none	32,565,672
>
> v1 -> v2:
> - Rebase
>    - usr/Makefile and init/Kconfig were changed so the patches were updated
> - No functional changes except to rebase
> - Split the patches up into smaller chunks
>
> v2 -> v3:
> - Add *.zst to the .gitignore in patch 8
> - Style nits in patch 3
> - Rename the PREBOOT macro to ZSTD_PREBOOT and XXH_PREBOOT in patches
>    1 through 3
>
> v3 -> v4:
> - Increase the ZSTD_IOBUF_SIZE from 4KB to 128KB to improve performance.
>    With this change I switch from malloc() to large_malloc() for the
>    buffers.
> - Increase the maximum allowed window size from 8 MB to 128 MB, which is
>    the max that zstd in the kernel supports.

Tested-by: Gabriel Craciunescu <nix.or.die@xxxxxxxxx>

> Best,
> Nick Terrell
>
> Adam Borowski (1):
>    .gitignore: add ZSTD-compressed files//
>
> Nick Terrell (7):
>    lib: prepare zstd for preboot environment
>    lib: prepare xxhash for preboot environment
>    lib: add zstd support to decompress
>    init: add support for zstd compressed kernel
>    usr: add support for zstd compressed initramfs
>    x86: bump ZO_z_extra_bytes margin for zstd
>    x86: Add support for ZSTD compressed kernel
>
>   .gitignore                        |   1 +
>   Documentation/x86/boot.rst        |   6 +-
>   arch/x86/Kconfig                  |   1 +
>   arch/x86/boot/compressed/Makefile |   5 +-
>   arch/x86/boot/compressed/misc.c   |   4 +
>   arch/x86/boot/header.S            |   8 +-
>   arch/x86/include/asm/boot.h       |   6 +-
>   include/linux/decompress/unzstd.h |  11 +
>   init/Kconfig                      |  15 +-
>   lib/Kconfig                       |   4 +
>   lib/Makefile                      |   1 +
>   lib/decompress.c                  |   5 +
>   lib/decompress_unzstd.c           | 342 ++++++++++++++++++++++++++++++
>   lib/xxhash.c                      |  21 +-
>   lib/zstd/decompress.c             |   2 +
>   lib/zstd/fse_decompress.c         |   9 +-
>   lib/zstd/zstd_internal.h          |  14 +-
>   scripts/Makefile.lib              |  15 ++
>   usr/Kconfig                       |  20 ++
>   usr/Makefile                      |   1 +
>   20 files changed, 464 insertions(+), 27 deletions(-)
>   create mode 100644 include/linux/decompress/unzstd.h
>   create mode 100644 lib/decompress_unzstd.c