feat: VRAM booster for the Steam Machine

lib/vram-booster.sh

@@ -0,0 +1,51 @@
+#!/bin/bash
+# "VRAM booster" menu item (vram), a sub-option of Steam Machine support
+# ticked along with it (opt-out), like SteamOS 3.9's dGPU VRAM management:
+# the game in front keeps its VRAM, background apps are evicted first, so a
+# game on the 8 GB GPU doesn't spill into system RAM and stutter. The kernel
+# side is the dmem cgroup controller (7.2); CachyOS packages the userspace
+# side: dmemcg-booster (a system service that enables the controller and
+# sets the limits, plus a user service) and plasma-foreground-booster, which
+# tells it which window is in front on the desktop. The latter only starts
+# with "autostart" set in kcgroupsrc.
+# Sourced by steamify.sh; not meant to be run on its own.
+
+VRAM_PKGS=(dmemcg-booster plasma-foreground-booster)
+
+vram_status() {
+    pacman -Q "${VRAM_PKGS[@]}" >/dev/null 2>&1 &&
+        systemctl is-enabled -q dmemcg-booster-system.service 2>/dev/null &&
+        systemctl --user is-enabled -q dmemcg-booster-user.service 2>/dev/null
+}
+
+vram_enable() {
+    local p missing=()
+    info "Installing the VRAM booster (the game in front keeps its VRAM)..."
+    for p in "${VRAM_PKGS[@]}"; do pacman -Q "$p" >/dev/null 2>&1 || missing+=("$p"); done
+    if ((${#missing[@]})); then
+        sudo pacman -S --needed --noconfirm "${missing[@]}" ||
+            { err "Installing ${missing[*]} failed."; return 1; }
+        state_set vram installed_pkgs "${missing[*]}"
+    fi
+    sudo systemctl enable --now dmemcg-booster-system.service >/dev/null 2>&1 ||
+        { err "Starting dmemcg-booster failed."; return 1; }
+    systemctl --user enable --now dmemcg-booster-user.service >/dev/null 2>&1 ||
+        { err "Starting dmemcg-booster for $USER failed."; return 1; }
+    kset vram kcgroupsrc "Foreground Booster" autostart true
+    # Started by the Plasma session from now on; start it in this one too.
+    [[ "${XDG_CURRENT_DESKTOP:-}" == KDE ]] &&
+        systemctl --user start plasma-foreground-booster.service >/dev/null 2>&1
+    ok "VRAM booster on: the game in front keeps its VRAM."
+}
+
+vram_disable() {
+    local pkgs
+    systemctl --user disable --now plasma-foreground-booster.service dmemcg-booster-user.service >/dev/null 2>&1
+    sudo systemctl disable --now dmemcg-booster-system.service >/dev/null 2>&1
+    krevert vram
+    pkgs="$(state_get vram installed_pkgs)"
+    # shellcheck disable=SC2086 # a list of package names
+    [[ -n "$pkgs" ]] && sudo pacman -Rns --noconfirm $pkgs >/dev/null 2>&1
+    state_clear vram
+    ok "VRAM booster off."
+}