On 12/19/23 20:19, Askar Safin wrote: > 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. I wrote that around 2005. >> This currently does not work when root= is provided since then >> saved_root_name contains a string and rootfstype= is ignored. I wrote the code to populate a tmpfs from initramfs in 2013 (8 years later), because nobody else had bothered to, and I've had a patch to fix the rootfstype= issue for years, but I long ago lost my touch with linux-kernel proctology: https://lkml.iu.edu/hypermail/linux/kernel/2302.2/05601.html Last I heard it was going upstream via somebody else (who tripled the size of the fix for no obvious reason, but that's modern linux-kernel for you), but I lost track after the guy who'd said to send it to him instead did multiple automated bounces from a bot that said "to save this one special guy's time, we're going to spam linux-kernel with autogenerated content delivered to tens of thousands of plebian mailboxes": https://lkml.iu.edu/hypermail/linux/kernel/2311.1/05544.html https://lkml.iu.edu/hypermail/linux/kernel/2311.1/06448.html Last I saw the rewrite of the fix had been resubmitted to the Special Guy a fourth time: https://lkml.iu.edu/hypermail/linux/kernel/2311.2/02938.html Maybe it'll show up in a git pull someday? Who knows... > Therefore, >> ramfs is currently always chosen when root= is provided. > > Maybe it is a good idea to just fully remove ramfs? "Let's delete a 20 year old filesystem that's been built into every system that whole time, this can't POSSIBLY have any side effects." We've already discussed this, more than once: https://lkml.iu.edu/hypermail/linux/kernel/2311.0/00435.html Can you build tmpfs on a nommu system? Last I checked the plumbing expects swap, but it's been a while... > 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. No, ramfs came first, tmpfs was created later. Not just what initramfs uses, but the order in which the filesystems were written. I believe modern ramfs more or less dates to Al Viro factoring out "libfs": https://lwn.net/Articles/57369/ Although the memory grows a bit hazy. (I vaguely remember what happened, but exactly when it was, and what came before what... git log in my unified history tree is showing fs/ramfs originating from 2.3.99pre4 in 2000 but it may be confused by a rename. I remember somebody, I thought Linus, saying that ramfs was an example user of the libfs code...) > Here are my configs (x86_64). Just enough to run busybox in "qemu -serial stdio" Back when I maintained busybox there were people in that space who cared about 14k, and that's not measuring runtime overhead. There was a lovely ELC talk in 2015 about booting Linux in 256 kilobytes of SRAM (everything else being XIP out of ROM-alikes), but alas the entire year's videos got wiped by the Linux Foundation. The PDF is still online though: https://elinux.org/images/9/90/Linux_for_Microcontrollers-_From_Marginal_to_Mainstream.pdf Alas, XIP got replaced with DAX which I've never managed to get to work... Rob
