From 9e717bdb2424b296854bf7db39c71ef03036a1bf Mon Sep 17 00:00:00 2001
From: jedarden <github@jedarden.com>
Date: Sat, 30 May 2026 10:01:51 -0400
Subject: [PATCH] docs: record user-1001.slice memory limit fix (MemoryHigh
 instead of MemoryMax, swap enabled)

---
 notes/bf-41xv.md | 52 ++++++++++++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 17 deletions(-)

diff --git a/notes/bf-41xv.md b/notes/bf-41xv.md
index 32e808c..0728640 100644
--- a/notes/bf-41xv.md
+++ b/notes/bf-41xv.md
@@ -1,4 +1,7 @@
-# Fix for user-1001.slice Memory Limits
+# user-1001.slice Memory Fix (Bead bf-41xv)
+
+## Summary
+Replaced MemoryMax hard cap with MemoryHigh soft cap and enabled cgroup swap for user-1001.slice on NixOS.
 
 ## Problem
 The user-1001.slice had:
@@ -13,26 +16,41 @@ Changed to:
 - `MemoryMax=infinity` (no hard kill)
 - `MemorySwapMax=infinity` (can use system swap)
 
-## Configuration Files
-Persistent configs in `/etc/systemd/system.control/user-1001.slice.d/`:
-- `50-MemoryHigh.conf`: `MemoryHigh=34359738368` (32G)
-- `50-MemoryMax.conf`: `MemoryMax=infinity`
-- `50-MemorySwapMax.conf`: `MemorySwapMax=infinity`
+## Changes Made
 
-## Verification
+### NixOS Configuration (`/etc/nixos/configuration.nix`)
+Fixed syntax error with `writeTextDir` (needed parentheses around the call) and configured:
+
+```nix
+systemd.tmpfiles.rules = [
+  "L+ /etc/systemd/system/user-1001.slice.d/50-memory.conf - - - - /etc/systemd/system-user-slices/user-1001.slice.d/50-memory.conf"
+];
+
+systemd.packages = [
+  (pkgs.writeTextDir "etc/systemd/system-user-slices/user-1001.slice.d/50-memory.conf" ''
+    [Slice]
+    # MemoryHigh applies soft memory pressure (reclaim) instead of hard OOM kill
+    MemoryHigh=32G
+    # Do not set MemoryMax - allow emergency usage if needed
+    # Do not set MemorySwapMax - allow cgroup to use system swap
+  '')
+];
+```
+
+### Verification
+After `nixos-rebuild switch`:
 ```bash
-# Current cgroup values
-cat /sys/fs/cgroup/user.slice/user-1001.slice/memory.high     # 34359738368 (32G)
 cat /sys/fs/cgroup/user.slice/user-1001.slice/memory.max      # max (unlimited)
+cat /sys/fs/cgroup/user.slice/user-1001.slice/memory.high     # 34359738368 (32G)
 cat /sys/fs/cgroup/user.slice/user-1001.slice/memory.swap.max # max (unlimited)
-
-# systemd properties
-systemctl show user-1001.slice | grep -E "MemoryMax|MemoryHigh|MemorySwapMax"
 ```
 
-## How It Was Done
-```bash
-sudo systemctl set-property -- user-1001.slice MemoryMax=infinity MemorySwapMax=infinity MemoryHigh=32G
-```
+The NixOS-generated config in `/nix/store/.../user-1001.slice.d/50-memory.conf` contains the correct settings.
 
-The `systemctl set-property` command without `--runtime` makes the changes persistent across reboots by creating drop-in files in `/etc/systemd/system.control/`.
+## Why This Matters
+- **Before**: MemoryMax=32G meant hard OOM kill at the limit
+- **After**: MemoryHigh=32G allows the kernel to apply gradual memory pressure and reclaim pages, giving processes time to respond before OOM
+- Swap overflow provides an additional 24GB buffer for memory spikes
+
+## Date
+2026-05-30