insmods will consider all arguments as optional modules by default, but
for squash module, all listed modules are required, if any of them is
missing the initramfs won't boot. So pass the '-c' argument to let instmos
know all those modules are mandatory, it will fail and give an error if
it failed to install any of those modules.
When building squash image, squash module forgot to install the new
shutdown.sh, and the shutdown hooks are always skipped on ordinary
shutdown if squash module is enabled.
The new shutdown.sh will remount the squash image and then everything
will just work, but currently re-mounting the squash image on shutdown
may have selinux problem and make the system hang, and there is no
easy way to fix it.
So skip fixing the shutdown.sh not being install problem, instead
just drop the new shutdown.sh, and unsquash the image on ordinary
shutdown, which is safer and should always work.
Signed-off-by: Kairui Song <kasong@redhat.com>
The only time we need to cleanup squahfs manually is on switch root, to
release resource and memory. We've covered that by setting
"Conflicts=initrd-switch-root.target" for squash cleanup service.
On shutdown systemd will take care of squahfs mounts. But for other
isolate, files in initramfs are most likely still required, so don't
clean up squahfs. For example, kdump's emergency handler will isolate
into its own target, if squahfs is cleaned up it will fail.
Signed-off-by: Kairui Song <kasong@redhat.com>
With all files stored in ramfs, and most of them are not compressed,
the initramfs will take up a lot of memory. Besides, if the file number
is large, each file will waste some memory due to page fragmetation.
This is due to ramfs' design, at least one page will be allocated for
one file however small the file is. On machine with large page size,
this will become worse and waste too many memory.
One approach to reducing the memory usage is to reduce the number of
files that got directly loaded into the root ramfs, and compress files
by put most files will into a read-only squash image and keep a minimum
set of executable and libraries outside as the loader for the squash
image. After the squash image is mounted, the real 'init' will be
executed and then everything behaves as usual.
This patch will introduce a '99squash' module which will never be
included by default. User can force add it, and if it is included,
dracut will perform some extra steps before creating the final image:
For now, "/etc" and "/usr" will be moved into the squashfs image.
"/init" will be renamed to "/init.stock" and replaced by "/init.squash".
Files and folders need to be accessible before mounting the image will
be still avaliable at their original place. And due to squashfs is
readonly, an overlayfs layer will be created on top of squashfs mount
point, as many dracut module require readwrite access to "/etc" and
"/usr", "init.squash" will ultimately call "/init.stock".
An extra systemd service will be installed. This service will umount all
squashfs related mount points right before switch-root to release
resources properly. This service will not actually do anything if
switch-root is not used.
This is very helpful when mem resource is very limited, like Kdump.
According to my tests, this squash module can help save about 35MB of
memory with 64K page size, or about 15MB with 4K page size on an
ordinary kdump capture routine. This module could also help reduce
memory usage for normal boot up process.
Won't change any behavior if squash module is not enabled.
Signed-off-by: Kairui Song <kasong@redhat.com>
Kairui Song