Use mglru_min_ttl_ms=1000 as default

Author: bigbruno

include/swap-default.conf

@@ -88,3 +88,13 @@ swap_mode=auto
 ## swapfile_loop_scheduler=auto    # I/O scheduler: auto, kyber, bfq, mq-deadline, none
 ## swapfile_loop_backing_fs=auto   # Backing filesystem: auto (host fs), f2fs
 
+################################################################################
+# MGLRU (Multi-Gen LRU) Settings
+#
+# MGLRU protects the working set from premature eviction (kernel 6.1+).
+# min_ttl_ms sets the minimum age before a page can be reclaimed.
+# Higher values = more protection, less reclaim.
+################################################################################
+
+## mglru_min_ttl_ms=1000           # Pages younger than this (ms) are never reclaimed
+

src/autoconfig.rs

@@ -92,6 +92,9 @@ pub struct RecommendedConfig {
     pub swapfc_free_ram_perc: u8,
     pub swapfc_free_swap_perc: u8,
     pub swapfc_remove_free_swap_perc: u8,
+
+    // MGLRU settings
+    pub mglru_min_ttl_ms: u32,
 }
 
 impl Default for RecommendedConfig {
@@ -112,6 +115,7 @@ impl RecommendedConfig {
             swapfc_free_ram_perc: defaults::SWAPFILE_FREE_RAM_PERC,
             swapfc_free_swap_perc: defaults::SWAPFILE_FREE_SWAP_PERC,
             swapfc_remove_free_swap_perc: defaults::SWAPFILE_REMOVE_FREE_SWAP_PERC,
+            mglru_min_ttl_ms: defaults::MGLRU_MIN_TTL_MS,
         }
     }
 
@@ -129,6 +133,7 @@ impl RecommendedConfig {
             swapfc_free_ram_perc: defaults::SWAPFILE_FREE_RAM_PERC,
             swapfc_free_swap_perc: defaults::SWAPFILE_FREE_SWAP_PERC,
             swapfc_remove_free_swap_perc: defaults::SWAPFILE_REMOVE_FREE_SWAP_PERC,
+            mglru_min_ttl_ms: defaults::MGLRU_MIN_TTL_MS,
         }
     }
 
@@ -160,6 +165,9 @@ impl RecommendedConfig {
             ]);
         }
 
+        // MGLRU: always inject so auto mode configures it
+        pairs.push(("mglru_min_ttl_ms", self.mglru_min_ttl_ms.to_string()));
+
         pairs
     }
 

src/defaults.rs

@@ -40,3 +40,7 @@ pub const SWAPFILE_FREQUENCY: u32 = 1;
 pub const SWAPFILE_SHRINK_THRESHOLD: u8 = 30;
 pub const SWAPFILE_SAFE_HEADROOM: u8 = 40;
 pub const SWAPFILE_NOCOW: &str = "1";
+
+// ── MGLRU (Multi-Gen LRU) ──────────────────────────────────────────────────
+
+pub const MGLRU_MIN_TTL_MS: u32 = 1000;

src/main.rs

@@ -160,6 +160,39 @@ fn disable_zswap_for_zram() {
 }
 
 
+/// Configure MGLRU anti-thrashing protection
+/// Sets min_ttl_ms which protects the working set from premature eviction
+fn configure_mglru(config: &Config, recommended: Option<&RecommendedConfig>) {
+    const MGLRU_MIN_TTL_PATH: &str = "/sys/kernel/mm/lru_gen/min_ttl_ms";
+
+    // Check if MGLRU is available
+    if !Path::new(MGLRU_MIN_TTL_PATH).exists() {
+        return;
+    }
+
+    // Get configured value, or use recommended value from autoconfig
+    let min_ttl_ms: u32 = config
+        .get_opt("mglru_min_ttl_ms")
+        .and_then(|v| v.parse::<u32>().ok())
+        .unwrap_or_else(|| {
+            recommended
+                .map(|r| r.mglru_min_ttl_ms)
+                .unwrap_or(defaults::MGLRU_MIN_TTL_MS)
+        });
+
+    if min_ttl_ms == 0 {
+        return;
+    }
+
+    // Apply the setting
+    match fs::write(MGLRU_MIN_TTL_PATH, min_ttl_ms.to_string()) {
+        Ok(_) => info!(
+            "MGLRU: min_ttl_ms = {} (working set protection)",
+            min_ttl_ms
+        ),
+        Err(e) => warn!("MGLRU: failed to set min_ttl_ms: {}", e),
+    }
+}
 
 /// Start the swap daemon
 fn start() -> Result<(), Box<dyn std::error::Error>> {
@@ -208,6 +241,9 @@ fn start() -> Result<(), Box<dyn std::error::Error>> {
         config.apply_autoconfig(&recommended);
     }
 
+    // Configure MGLRU early (protects working set during swap operations)
+    configure_mglru(&config, Some(&recommended));
+
     // Determine effective mode
     let effective_mode = match swap_mode {
         SwapMode::Auto => match recommended.swap_mode {