On Sun, Nov 19, 2023 at 08:12:48PM -0500, Stefan Berger wrote: > Documentation/filesystems/ramfs-rootfs-initramfs.rst states: > > If CONFIG_TMPFS is enabled, rootfs will use tmpfs instead of ramfs by > default. To force ramfs, add "rootfstype=ramfs" to the kernel command > line. > > This currently does not work when root= is provided since then > saved_root_name contains a string and rootfstype= is ignored. Therefore, > ramfs is currently always chosen when root= is provided. Maybe it is a good idea to just fully remove ramfs? initramfs will always be tmpfs. And tmpfs will always be enabled. As well as I understand, ramfs was originally introduced, because tmpfs seemed too big. So, it seemed to be a good idea to have small fs (ramfs), which is always enabled. I just did an experiment. I compiled the kernel with a very small config. And without TMPFS and SHMEM. I got 1059440 bytes image. Then I enabled TMPFS and SHMEM, and I got 1072976 bytes. So tmpfs adds 13536 bytes, i. e. 14k, which is a very small amount. It adds 1.3 % to the kernel even with very small config. So I propose to remove ramfs and always enable tmpfs. This will decrease complexity. Here are my configs (x86_64). Just enough to run busybox in "qemu -serial stdio" make KCONFIG_ALLCONFIG="$FILE" allnoconfig CONFIG_64BIT=y CONFIG_PRINTK=y CONFIG_SERIAL_8250=y CONFIG_TTY=y CONFIG_SERIAL_8250_CONSOLE=y CONFIG_BLK_DEV_INITRD=y CONFIG_RD_GZIP=y CONFIG_BINFMT_ELF=y CONFIG_EMBEDDED=y CONFIG_EXPERT=y CONFIG_TMPFS=n # Try to change this to "y" CONFIG_SHMEM=n # Try to change this to "y" Here is full docker reproducer: # Reproducible # 20230227 = 20230227T000000Z = 20230226T090712Z FROM debian:sid-20230227 ENV LC_ALL C.UTF-8 RUN sed -i 's~^URIs:.*$~URIs: http://snapshot.debian.org/archive/debian/20230226T090712Z~' /etc/apt/sources.list.d/debian.sources RUN echo 'Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/02acquire-check-valid-until RUN apt-get update && apt-get install -y apt-utils whiptail RUN apt-get update && apt-get install -y busybox-static qemu-system-x86 make gcc git flex bison bc libelf-dev less nano cpio RUN git clone --depth=1 -b v6.2 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git RUN : > /.config # See Linux f8f0d06438e5c810d1e13b5f8c2fed501fe36e9c RUN echo 'CONFIG_64BIT=y' >> /.config RUN echo 'CONFIG_PRINTK=y' >> /.config RUN echo 'CONFIG_SERIAL_8250=y' >> /.config RUN echo 'CONFIG_TTY=y' >> /.config RUN echo 'CONFIG_SERIAL_8250_CONSOLE=y' >> /.config RUN echo 'CONFIG_BLK_DEV_INITRD=y' >> /.config RUN echo 'CONFIG_RD_GZIP=y' >> /.config RUN echo 'CONFIG_BINFMT_ELF=y' >> /.config RUN echo 'CONFIG_EMBEDDED=y' >> /.config RUN echo 'CONFIG_EXPERT=y' >> /.config RUN echo 'CONFIG_TMPFS=y' >> /.config # try "n" RUN echo 'CONFIG_SHMEM=y' >> /.config # try "n" RUN cd linux && make KCONFIG_ALLCONFIG=/.config allnoconfig RUN cd linux && make -j4 RUN mkdir /initramfs && cp /bin/busybox /initramfs && cd /initramfs && ln -s busybox sh && find . | cpio --create --format=newc --quiet | gzip > /initramfs.cpio.gz RUN echo "qemu-system-x86_64 -M microvm -m 64M -serial stdio -display none -kernel /linux/arch/x86/boot/bzImage -initrd /initramfs.cpio.gz -append 'quiet console=ttyS0 earlyprintk=ttyS0 rdinit=/sh' -nodefaults -no-user-config" > /root/.bash_history -- Askar Safin
