On Thu, Mar 19, 2020 at 12:59:26PM -0700, Nick Terrell wrote: > Hi all, > > 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 > > 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. > > 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 > > 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 | 338 ++++++++++++++++++++++++++++++ > 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, 460 insertions(+), 27 deletions(-) > create mode 100644 include/linux/decompress/unzstd.h > create mode 100644 lib/decompress_unzstd.c This looks good to me! Please consider the series: Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Thanks! -Kees -- Kees Cook
