postmarketos-base: enable using zram swap by default (MR 3752)

This installs zram-init and sets it to start on boot for all
devices/UIs. The included conf.d/zram-init also allows diabling using
zram swap or overriding the size by using a deviceinfo var.

I did an analysis of the pmos base install size with the 'none' UI
selected, after depending on zram-init, and the following new package is
installed:
        zram-init-11.1-r1 installed size: 40 KiB

These packages are dependencies of zram-init, however they are already
installed in the base image (with 'none' UI) so they are not counted
above:
        util-linux-misc-2.38.1-r0 installed size: 6816 KiB
        e2fsprogs-extra-1.46.5-r4 installed size: 1324 KiB

So this seems like a very small price to pay for the benefit of not
making the logic/implementation more complicated than this.

     * Starting busybox syslog ... [ ok ]
    ssh-keygen: generating new host keys: RSA ECDSA ED25519
     * Starting sshd ... [ ok ]
    zram swap: activating with size: 243 MB
     * Loading zram module...
     [ ok ]
     * Swap->zram0
     [ ok ]
     * Starting local ... [ ok ]

This change introduces one new deviceinfo variable:
deviceinfo_zram_swap_pct: percentage of RAM to use for zram swap

Default percentages if the second var is unset are explained in the
zram-init file this commit adds. A value of 0 disables zram swap.

fixes #1133

main/postmarketos-base/APKBUILD

@@ -1,5 +1,5 @@
 pkgname=postmarketos-base
-pkgver=24.1
+pkgver=25
 pkgrel=0
 pkgdesc="Meta package for minimal postmarketOS base"
 url="https://postmarketos.org"
@@ -13,6 +13,7 @@ depends="
 	postmarketos-mvcfg
 	postmarketos-keys
 	cmd:sudo
+	zram-init
 	"
 install="$pkgname.post-install $pkgname.pre-upgrade $pkgname.post-upgrade"
 triggers="$pkgname.trigger=/etc"
@@ -33,6 +34,7 @@ replaces="
 	busybox-openrc
 	openrc
 	sudo
+	zram-init-openrc
 	"
 replaces_priority=100  # leave plenty for alpine
 
@@ -43,6 +45,7 @@ _source440="
 _source644="
 	etc/conf.d/bootmisc
 	etc/conf.d/swapfile
+	etc/conf.d/zram-init
 	etc/conf.d/syslog
 	etc/fstab
 	etc/issue
@@ -122,6 +125,7 @@ e529f5cef1f31481b577f99b8917704f2cfefb963d98bf40a14b017938e55a00134d2033f81d2cb0
 9591c9cb2194fa1092505159c9eb3d899bec95b6dbd9a0222be62098db012da113a125e40d70373d60af9880dfa489bdbe12b6b897bdef5613e023800fb6ee1b  rootfs-etc-doas.d-10-postmarketos.conf
 a5c6bfaf6ee41f9623f463b64dab95924453d7b70bdd114cc441be9fc68fb6b0e042ae3163ec357d0dd6db93767232224b8c03df29f2cadf3ac2c6e2c998784f  rootfs-etc-conf.d-bootmisc
 e0d2d48b82a03239a4c0a00acaf83e00d397c23a8d7c71053d4e2a383357c22dcedef9e81b0e12a1d7514e1fdbe0bb3eb82613d18b29034a7ce5447f13c84a53  rootfs-etc-conf.d-swapfile
+488440c14ff7a662a6a0e5cad9caed1a972f82d2361b4985a68c3f05fab0a3fe9c58887907e66f683c8f8b6c12ba7e17cafdec1aa72cd9055190bd9f7a14c888  rootfs-etc-conf.d-zram-init
 e4576c58c35f80bedddb1e89e186f37d31a186d3e9eb046581b8c5d7b7d435e18924539e851d3e67dc0ede80f9d44d16bd9ef52e73350d3f13224edc31d73a34  rootfs-etc-conf.d-syslog
 9b8d0493bb64457fe176fea801e0771d3c5279302c61559824bf81b3d2b66d2c1e076f4aaac65f55389005acb18c27e44bed858c2bdbad37d74199f07c86c354  rootfs-etc-fstab
 45bd0742a64a9d3c4a88e152b97edcf3fa1edca28884f9ea69e7c4c365f1e41ef9056dbe204545de7d4b2ba92e1e5872b2a929c2dcc1dd468e627cc3f090b8e6  rootfs-etc-issue

main/postmarketos-base/postmarketos-base.post-install

@@ -13,7 +13,7 @@ done
 for service in hwclock modules sysctl hostname bootmisc syslog; do
 	rc-update -q add $service boot
 done
-for service in sshd swapfile local; do
+for service in sshd swapfile local zram-init; do
 	rc-update -q add $service default
 done
 for service in mount-ro killprocs savecache; do

main/postmarketos-base/rootfs-etc-conf.d-zram-init

@@ -0,0 +1,55 @@
+. /etc/deviceinfo
+
+# Size defaults to:
+# - 75% of RAM for devices with 2GB of RAM or less
+# - 50% of RAM for devices with between 2GB and 6GB of RAM
+# - 25% of RAM for devices with greater 6GB of RAM
+# This is loosely based on some data here:
+# https://gitlab.com/postmarketOS/pmaports/-/merge_requests/3752#note_1229631449
+
+_mem_size_mb="$(LC_ALL=C free -m | awk '/^Mem:/{print $2}')"
+
+if [ $_mem_size_mb -le 2048 ]; then
+        _size_pct=75
+elif [ $_mem_size_mb -gt 6144 ]; then
+        _size_pct=25
+else
+        _size_pct=50
+fi
+
+# Allow overriding the size as a percentage of RAM using a deviceinfo var, or
+# disabling it completely
+if [ -n "$deviceinfo_zram_swap_pct" ]; then
+
+        # 0% --> disable zram swap
+        if [ "$deviceinfo_zram_swap_pct" == "0" ]; then
+                echo "zram swap: disabled in deviceinfo, exiting"
+                exit 0
+        fi
+
+        _size_pct="$deviceinfo_zram_swap_pct"
+fi
+
+size0=$(($_mem_size_mb * $_size_pct / 100))
+
+echo "zram swap: activating with size: $size0 MB"
+# zstd (since linux-4.18), lz4 (since linux-3.15), or lzo.
+# Size: zstd (best) > lzo > lz4. Speed: lz4 (best) > zstd > lzo
+algo0=zstd 
+
+# The following are defaults from the zram-init package:
+load_on_start=yes
+unload_on_stop=yes
+num_devices=1
+type0=swap
+flag0= # The default "16383" is fine for us
+mlim0= # no hard memory limit
+back0= # no backup device
+icmp0= # no incompressible page writing to backup device
+idle0= # no idle page writing to backup device
+wlim0= # no writeback_limit for idle page writing for backup device
+notr0= # keep the default on linux-3.15 or newer
+maxs0=1 # maximum number of parallel processes for this device
+labl0=zram_swap # the label name
+uuid0= # Do not force UUID
+args0= # we could e.g. have set args0="-L 'zram_swap'" instead of using labl0