docs: add resource limits guide for low-RAM devices

- README: new section explaining WG_MEM_LIMIT / WG_MEMSWAP_LIMIT with
  per-RAM-tier values and host swap configuration for SBC boards
- CLAUDE.md: simplify resource limits table, drop device-specific
  measurements, reference README for per-board guidance
- .env.example: update comments with per-tier values and OOM warning

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -17,11 +17,17 @@ WG_UI_PORT=51821
 
 # --- OPZIONALI — Limiti risorse container (SBC) ---
 # Decommenta e adatta alla RAM disponibile:
-#   512 MB RAM → WG_MEM_LIMIT=128m
-#   1 GB RAM   → WG_MEM_LIMIT=256m  (default)
-#   2 GB+ RAM  → WG_MEM_LIMIT=384m
+#   512 MB RAM (RPi 3B)   → WG_MEM_LIMIT=96m   (reale: ~37 MB, 96 m è già doppio)
+#   1 GB RAM   (RPi 3B+)  → WG_MEM_LIMIT=128m
+#   2 GB+ RAM  (RPi 4/5)  → WG_MEM_LIMIT=256m  (default)
 # Tenere WG_MEMSWAP_LIMIT = WG_MEM_LIMIT per disabilitare lo swap del container.
 # Su single-core (Pi Zero / Pi 1) impostare WG_CPUS=0.75.
+#
+# ATTENZIONE — RPi 3 con uptime lungo: il processo Node.js può crescere nel
+# tempo. Con 1 GB di RAM totale e OS+Docker che occupano ~350 MB, un limite
+# di 256 m lascia pochissimo margine; il kernel OOM-killa SSH prima del
+# container. Usare 96-128 m e assicurarsi che lo swap host sia >= 512 MB
+# (vedi CLAUDE.md §SBC per il comando).
 # WG_MEM_LIMIT=256m
 # WG_MEMSWAP_LIMIT=256m
 # WG_CPUS=1.0

CLAUDE.md

@@ -60,12 +60,12 @@ Affects mostly SBC boards with custom BSP kernels, but can occur on any host whe
 
 The `wg-init` service handles this automatically: it runs `modprobe ip6_tables ip6table_nat` (with `SYS_MODULE` cap and `/lib/modules` bind-mounted read-only) before wg-easy starts. Failures are silenced (`|| true`) so the setup works on kernels where these modules are built-in or unavailable.
 
-**Resource limits** (`docker-compose.yml`):
+**Resource limits** (override via `.env`):
 
-| Variable | Default | Purpose |
+| Variable | Default | Notes |
 |---|---|---|
-| `WG_MEM_LIMIT` | `256m` | Hard memory cap for wg-easy |
-| `WG_MEMSWAP_LIMIT` | `256m` | Disables swap (swap = mem limit) |
-| `WG_CPUS` | `1.0` | CPU share (1 core) |
+| `WG_MEM_LIMIT` | `256m` | Hard cap for the wg-easy container |
+| `WG_MEMSWAP_LIMIT` | `256m` | Keep equal to `WG_MEM_LIMIT` to disable container swap |
+| `WG_CPUS` | `1.0` | `0.75` on single-core boards (Pi Zero, Pi 1) |
 
-Lower `WG_MEM_LIMIT` to `128m` on boards with less than 1 GB RAM. Do not set it below `96m` or the Node.js runtime will OOM-kill on startup.
+The limit exists to prevent Node.js from slowly growing over long uptime and triggering the host OOM-killer (symptom: SSH becomes unreachable). Do not go below `96m` or the runtime OOM-kills on startup. See README §Dispositivi a risorse limitate for per-board guidance and swap configuration.

README.md

@@ -75,6 +75,32 @@ vpn/
 
 ---
 
+## Dispositivi a risorse limitate (SBC)
+
+Su board con poca RAM (≤ 1 GB) il processo Node.js di wg-easy può crescere nel tempo e far sì che il kernel OOM-killi altri processi di sistema — SSH compreso. Per evitarlo, decommenta e adatta questi valori nel tuo `.env`:
+
+```ini
+# Board con 512 MB RAM
+WG_MEM_LIMIT=96m
+WG_MEMSWAP_LIMIT=96m
+
+# Board con 1 GB RAM
+WG_MEM_LIMIT=128m
+WG_MEMSWAP_LIMIT=128m
+```
+
+Tieni `WG_MEMSWAP_LIMIT` uguale a `WG_MEM_LIMIT` per disabilitare lo swap del container: quando il container raggiunge il limite viene riavviato da Docker invece di consumare swap di sistema.
+
+Assicurati anche che lo swap dell'host sia almeno 512 MB. Su Raspberry Pi OS il default è 100 MB — per aumentarlo:
+
+```bash
+sudo dphys-swapfile swapoff
+sudo sed -i 's/CONF_SWAPSIZE=100/CONF_SWAPSIZE=512/' /etc/dphys-swapfile
+sudo dphys-swapfile setup && sudo dphys-swapfile swapon
+```
+
+---
+
 ## Aggiornare wg-easy
 
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