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ramdisk: the live root grows into half of memory

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The live root was a fixed 96 MB image in the kernel: 60 MB of zeros on
the ISO, twice, and room for 60 MB of packages whatever the machine had.

Now the image is only what the root holds, plus slack, measured by
building it once large. Past its end the ramdisk goes on to half of the
memory free at mount, as pages taken the first time each block is
written; an unwritten block reads as zeros and costs nothing. SchFS
keeps no free-space map on disk, so growing a volume is a larger total
before open builds the map: grow_to, set for the ramdisk root.

8 GB machine: a 4 GB root, Xorg installed into it in 77 s with 7.6 GB
still free. The ISO is 172 MB instead of 344.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
This commit is contained in:
Nexoniarz 2026-10-24 17:20:43 +02:00
commit d0941780f5
7 changed files with 120 additions and 13 deletions
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8
docs/plan/alpine.md
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@ -39,7 +39,7 @@ only what is its own (see `tools/posix/mkaroot.sh`):
## Building
make qemu boots build/schfs.img, the root as a 1 GB SchFS disk
make iso the same root as the live system's 96 MB ramdisk
make iso the same root as the live system's ramdisk
make alpine-lock re-resolve world against Alpine (needs the network)
It is the only root. sysroot/ is what schos-base is packaged from.
@ -68,8 +68,10 @@ All of it found by running apk:
## Next
- The live ISO runs the apk root from RAM: `apk add` works, into 59 MB, and
is gone at reboot. Keeping packages needs an installer that writes the root
- The live ISO runs the apk root from RAM. The image in the kernel is only
what the root holds; at boot the volume grows into half of the free memory
(4 GB of root on an 8 GB machine), backed by pages as they are written.
Xorg installs into it in about a minute. All of it is gone at reboot. Keeping packages needs an installer that writes the root
to a SATA or NVMe disk, and a kernel that finds its root there by the
SchFS GPT type rather than as IDE disk 1.
- Xorg from apk (`xorg-server xf86-video-fbdev xf86-input-evdev`) instead of