Bug#1106757: ppc64el Trixie: Need default 64KB page kernel or installer option
On 29/05/2025 at 21:19, Pascal Hambourg wrote:
On 29/05/2025 at 15:54, Cyril Brulebois wrote:
Trupti <trupti@linux.ibm.com> (2025-05-29):
Add a clear installer option to select a 64KB page kernel.
I believe this should be offered in expert mode, have you tried that?
AFAICS linux-image-powerpc64le-64k is not included in the DVD-1 image,
so it requires a network mirror. Same with linux-image-arm64-16k.
Thinking twice, DVD-1 and netinst images set up a network mirror only
after installing the base system, so they only offer kernel flavours
included in installation images. Only netboot images set up a network
mirror before installing the base system and offer all kernel flavours.
After reading #1079800 ("release-notes - Document that default ppc64el
kernel switched to 4k pages") [1], I thought about possible impact of
page size change on the installer, but do not have any ppc64 or arm64
hardware to test.
[1] <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1079800>
The kernel supports a swap space only if it matches the page size.
The kernel supports a btrfs filesystem with a sector size equal to the
page size or 4k (aka subpage block size support, see [2][3]).
[2] <https://btrfs.readthedocs.io/en/latest/Subpage.html>
[3]
<https://btrfs.readthedocs.io/en/latest/Status.html#status-subpage-block-size>
Bookworm:
- linux-image-powerpc64le has 64k page size.
- mkswap creates swap with 64k page size.
- mkfs.btrfs creates filesystem with 64k sector size.
Trixie:
- linux-image-powerpc64le has 4k page size.
- mkswap creates swap with 4k page size.
- mkfs.btrfs creates filesystem with 4k sector size.
1) Impact on reuse of existing swap and btrfs filesystem:
The installer can detect (via libparted) and use an existing swap only
if it matches the installer kernel page size (4k). So it cannot use a
swap space created by a previous version with 64k page size without
reformatting it. No big deal though.
The installer can detect (via libparted) an existing btrfs filesystem
regardless of its sector size but can use it only if its sector size is
4k. So it cannot use a btrfs filesystem created by a previous version
with 64k sector size without reformatting it (and losing all its data).
2) Impact if linux-image-powerpc64le-64k (or linux-image-arm64-16k on
arm64) is selected:
systemd.swap seems to run swapon with --fixpgsz which reinitializes the
swap space if it does not match the kernel page size, so swap page size
mismatch should be fixed automatically during first boot.
A kernel with 64k page size is said to support btrfs filesystems with
either 4k or 64k sector size, so it should be able to mount btrfs
filesystems with 4k sector size created by Trixie installer.
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