lmkd: adjust thrashing dection strategy am: 1f72f5fa4b

Original change: https://android-review.googlesource.com/c/platform/system/memory/lmkd/+/1414468

Change-Id: If2c66c905e2c5e73a946d9d19fa98a2c07a6fdf4

lmkd.cpp

@@ -100,6 +100,7 @@
 #define EIGHT_MEGA (1 << 23)
 
 #define TARGET_UPDATE_MIN_INTERVAL_MS 1000
+#define THRASHING_RESET_INTERVAL_MS 1000
 
 #define NS_PER_MS (NS_PER_SEC / MS_PER_SEC)
 #define US_PER_MS (US_PER_SEC / MS_PER_SEC)
@@ -2313,16 +2314,18 @@ static void mp_event_psi(int data, uint32_t events, struct polling_params *poll_
         DIRECT_RECLAIM,
     };
     static int64_t init_ws_refault;
+    static int64_t prev_workingset_refault;
     static int64_t base_file_lru;
     static int64_t init_pgscan_kswapd;
     static int64_t init_pgscan_direct;
     static int64_t swap_low_threshold;
     static bool killing;
-    static int thrashing_limit;
+    static int thrashing_limit = thrashing_limit_pct;
-    static bool in_reclaim;
     static struct zone_watermarks watermarks;
     static struct timespec wmark_update_tm;
     static struct wakeup_info wi;
+    static struct timespec thrashing_reset_tm;
+    static int64_t prev_thrash_growth = 0;
 
     union meminfo mi;
     union vmstat vs;
@@ -2338,6 +2341,7 @@ static void mp_event_psi(int data, uint32_t events, struct polling_params *poll_
     bool cut_thrashing_limit = false;
     int min_score_adj = 0;
     int swap_util = 0;
+    long since_thrashing_reset_ms;
 
     if (clock_gettime(CLOCK_MONOTONIC_COARSE, &curr_tm) != 0) {
         ALOGE("Failed to get current time");
@@ -2376,6 +2380,8 @@ static void mp_event_psi(int data, uint32_t events, struct polling_params *poll_
         /* Reset file-backed pagecache size and refault amounts after a kill */
         base_file_lru = vs.field.nr_inactive_file + vs.field.nr_active_file;
         init_ws_refault = vs.field.workingset_refault;
+        thrashing_reset_tm = curr_tm;
+        prev_thrash_growth = 0;
     }
 
     /* Check free swap levels */
@@ -2394,22 +2400,50 @@ static void mp_event_psi(int data, uint32_t events, struct polling_params *poll_
     } else if (vs.field.pgscan_kswapd > init_pgscan_kswapd) {
         init_pgscan_kswapd = vs.field.pgscan_kswapd;
         reclaim = KSWAPD_RECLAIM;
-    } else {
+    } else if (vs.field.workingset_refault == prev_workingset_refault) {
-        in_reclaim = false;
+        /* Device is not thrashing and not reclaiming, bail out early until we see these stats changing*/
-        /* Skip if system is not reclaiming */
         goto no_kill;
     }
 
-    if (!in_reclaim) {
+    prev_workingset_refault = vs.field.workingset_refault;
-        /* Record file-backed pagecache size when entering reclaim cycle */
+
+     /*
+     * It's possible we fail to find an eligible process to kill (ex. no process is
+     * above oom_adj_min). When this happens, we should retry to find a new process
+     * for a kill whenever a new eligible process is available. This is especially
+     * important for a slow growing refault case. While retrying, we should keep
+     * monitoring new thrashing counter as someone could release the memory to mitigate
+     * the thrashing. Thus, when thrashing reset window comes, we decay the prev thrashing
+     * counter by window counts. if the counter is still greater than thrashing limit,
+     * we preserve the current prev_thrash counter so we will retry kill again. Otherwise,
+     * we reset the prev_thrash counter so we will stop retrying.
+     */
+    since_thrashing_reset_ms = get_time_diff_ms(&thrashing_reset_tm, &curr_tm);
+    if (since_thrashing_reset_ms > THRASHING_RESET_INTERVAL_MS) {
+        long windows_passed;
+        /* Calculate prev_thrash_growth if we crossed THRASHING_RESET_INTERVAL_MS */
+        prev_thrash_growth = (vs.field.workingset_refault - init_ws_refault) * 100 / base_file_lru;
+        windows_passed = (since_thrashing_reset_ms / THRASHING_RESET_INTERVAL_MS);
+        /*
+         * Decay prev_thrashing unless over-the-limit thrashing was registered in the window we
+         * just crossed, which means there were no eligible processes to kill. We preserve the
+         * counter in that case to ensure a kill if a new eligible process appears.
+         */
+        if (windows_passed > 1 || prev_thrash_growth < thrashing_limit) {
+            prev_thrash_growth >>= windows_passed;
+        }
+
+        /* Record file-backed pagecache size when crossing THRASHING_RESET_INTERVAL_MS */
         base_file_lru = vs.field.nr_inactive_file + vs.field.nr_active_file;
         init_ws_refault = vs.field.workingset_refault;
+        thrashing_reset_tm = curr_tm;
         thrashing_limit = thrashing_limit_pct;
     } else {
         /* Calculate what % of the file-backed pagecache refaulted so far */
         thrashing = (vs.field.workingset_refault - init_ws_refault) * 100 / base_file_lru;
     }
-    in_reclaim = true;
+    /* Add previous cycle's decayed thrashing amount */
+    thrashing += prev_thrash_growth;
 
     /*
      * Refresh watermarks once per min in case user updated one of the margins.
@@ -2426,7 +2460,7 @@ static void mp_event_psi(int data, uint32_t events, struct polling_params *poll_
 
         calc_zone_watermarks(&zi, &watermarks);
         wmark_update_tm = curr_tm;
-     }
+    }
 
     /* Find out which watermark is breached if any */
     wmark = get_lowest_watermark(&mi, &watermarks);