Arch Linux

it should also be noted that, while certainly not recommended, this would theoretically allow the ISO to be run on systems with less than 256MB without editing the kernel commandline (assuming they're running from media and not trying to do copytoram).

actually, re-reading- i read this wrong. it looks like in that case _dm_snapshot() is not called, BUT for whatever reason the live environment overlay is still limited to 256M even with e.g. 4GB RAM, which seems ludicrous to me for a live CD. I'm not sure where that's being set, but it strikes me as a bit strange.

EDIT: it seems it's set at line 123. If a persistent image is not specified, I'd recommend setting a tmpfs to use the whole size of available RAM. tmpfs will grow (and shrink) as necessary, there should be no need to set this to a hard limit.

what is the final request? is there any limitation here? Waste of RAM where with tmpfs?

In any case you can not boot on system with less than 256MB with XY compression of initramfs, try it ;)

bingo! sorry, i wanted to test it first to make sure it'd cause the behaviour i expected.

so, if you do something like this:

--- /usr/lib/initcpio/hooks/archiso 2016-12-21 17:30:46.000000000 -0500
+++ archiso 2017-01-18 10:24:37.113333330 -0500
@@ -194,9 +194,15 @@
echo $(readlink -f ${cow_device}) >> /run/archiso/used_block_devices
mount -o remount,rw "/run/archiso/cowspace"
else
- msg ":: Mounting /run/archiso/cowspace (tmpfs) filesystem, size=${cow_spacesize}..."
- mkdir -p /run/archiso/cowspace
- mount -t tmpfs -o "size=${cow_spacesize}",mode=0755 cowspace /run/archiso/cowspace
+ if [[ "${cow_persistent}" != 'P' ]]; then
+ msg ":: Mounting /run/archiso/cowspace (tmpfs) filesystem, size=${cow_spacesize}..."
+ mkdir -p /run/archiso/cowspace
+ mount -t tmpfs -o "size=${cow_spacesize}",mode=0755 cowspace /run/archiso/cowspace
+ else
+ msg ":: Mounting /run/archiso/cowspace (tmpfs) filesystem..."
+ mkdir -p /run/archiso/cowspace
+ mount -t tmpfs -o mode=0755 cowspace /run/archiso/cowspace
+ fi
fi
mkdir -p -m 0700 "/run/archiso/cowspace/${cow_directory}"


it should do the trick. (might want to test it with persistent cow images though. works fine with copytoram).

result:

dev 2.0G 0 2.0G 0% /dev
run 2.0G 73M 1.9G 4% /run
/dev/sr0 2.4G 2.4G 0 100% /run/archiso/bootmnt
cowspace 2.0G 47M 1.9G 3% /run/archiso/cowspace
/dev/loop0 1.2G 1.2G 0 100% /run/archiso/sfs/airootfs
airootfs 2.0G 47M 1.9G 3% /
tmpfs 2.0G 0 2.0G 0% /dev/shm
tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup
tmpfs 2.0G 0 2.0G 0% /tmp
tmpfs 396M 0 396M 0% /run/user/0

edit: and the available RAM isn't affected. :)

[root@bdisk-live ~]# free -m
total used free shared buff/cache available
Mem: 3954 63 3323 118 566 3555
Swap: 0 0 0

whoops, that patch is gonna fail because of the munged whitespace. real patch attached.

I am trying to understand what is the last result? why a test on cow_persistent=? Such parameter is only used on dm-snapshot (non-default) mode as documented on docs/.
Looks related to old discussion  FS#45618 

PS: mkdir command is duplicated, patch uses tabs, while archiso use spaces, see .editorconfig/vim last line

i've never used persistent images in this manner, so i have no idea- but i PRESUME that's why you're creating a .cow in the first place and limiting the tmpfs size?

regardless; remove the if test if it isn't needed, but putting a size limitation on a tmpfs for a live environment is unnecessary. for an install and for something like /tmp it makes perfect sense, but not for a system designed to be run on RAM entirely.

(also- the above patch does not regress  FS#45618  - just tested)

Take cowspacesize as safeguard. The 256M limit is just sufficient for releng. If you want to change it, you have two options, at boot time, via parameter, or at runtime via resize tmpfs.

Sure I can remove the limit and left the 75% default for tmpfs and set parameter on releng profile. Such low limit on releng profile has two purposes: as said before is just sufficient for install/rescue procedure, and "avoid" install Arch on RAM, like many users do!, they will see error messages, instead of blank install.

Oh and there is one more thing, in dm-snapshot mode , such limit is for fs that does not support sparse files, like FAT.

Edit: maybe is time to remove dm-snapshot support since overlayfs works fine.

[...you have two options, at boot time, via parameter, or at runtime via resize tmpfs.]
What about a third option in the build script releng/build or releng/efiboot/loader/entries/archiso-x86_64-cd.conf, where one can specify the size according to his needs?. The later seems easier to just append cow_spacesize=SIZE at the end of the line, so that it reads "options archisobasedir=%INSTALL_DIR% archisolabel=%ARCHISO_LABEL% cow_spacesize=SIZE". Am just not sure if it would work this way and don't know the difference between the files archiso-x86_64-cd.conf and archiso-x86_64-usb.conf, I will have to try it.

third? its the same: boot time.

At boot time means to add it to the kernel parameters when the pc actually boots from the install media. What I mean is to have it "built in" by editing the boot loader config file {work_dir}/efiboot/loader/entries/archiso-x86_64-cd.conf. Anyway I tested it by adding cow_spacesize=1G as mentioned before and it worked.

Since this is not really related to what this bug report is about, let's come back to it. Sorry for hijacking.