simple_lmk: Use vmpressure notifier to trigger kills

Using kswapd's scan depth to trigger task kills is inconsistent and
unreliable. When memory pressure quickly spikes, the kswapd scan depth
trigger fails to kick off Simple LMK fast enough, causing severe lag.
Additionally, kswapd could stop scanning prematurely before reaching the
desired scan depth to trigger Simple LMK, which could also cause stalls.

To remedy this, use the vmpressure framework instead, since it provides
more consistent and accurate readings on memory pressure. This is not
very tunable though, so remove CONFIG_ANDROID_SIMPLE_LMK_AGGRESSION.
Triggering Simple LMK to kill when the reported memory pressure is 100
should yield good results on all setups.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>

drivers/android/Kconfig

@@ -67,28 +67,6 @@ config ANDROID_SIMPLE_LMK
 
 if ANDROID_SIMPLE_LMK
 
-config ANDROID_SIMPLE_LMK_AGGRESSION
-	int "Reclaim frequency selection"
-	range 1 3
-	default 1
-	help
-	  This value determines how frequently Simple LMK will perform memory
-	  reclaims. A lower value corresponds to less frequent reclaims, which
-	  maximizes memory usage. The range of values has a logarithmic
-	  correlation; 2 is twice as aggressive as 1, and 3 is twice as
-	  aggressive as 2, which makes 3 four times as aggressive as 1.
-
-	  The aggression is set as a factor of kswapd's scan depth. This means
-	  that a system with more memory will have a more expensive aggression
-	  factor compared to a system with less memory. For example, setting an
-	  aggression factor of 1 with 4 GiB of memory would be like setting a
-	  factor of 2 with 8 GiB of memory; the more memory a system has, the
-	  more expensive it is to use a lower value.
-
-	  Choosing a value of 1 here works well with systems that have 4 GiB of
-	  memory. If the default doesn't work well, then this value should be
-	  tweaked based on empirical results using different values.
-
 config ANDROID_SIMPLE_LMK_MINFREE
 	int "Minimum MiB of memory to free per reclaim"
 	range 8 512

drivers/android/simple_lmk.c

@@ -10,6 +10,7 @@
 #include <linux/moduleparam.h>
 #include <linux/oom.h>
 #include <linux/sort.h>
+#include <linux/vmpressure.h>
 #include <uapi/linux/sched/types.h>
 
 /* The minimum number of pages to free per reclaim */
@@ -267,13 +268,6 @@ static int simple_lmk_reclaim_thread(void *data)
 	return 0;
 }
 
-void simple_lmk_decide_reclaim(int kswapd_priority)
-{
-	if (kswapd_priority == CONFIG_ANDROID_SIMPLE_LMK_AGGRESSION &&
-	    !atomic_cmpxchg_acquire(&needs_reclaim, 0, 1))
-		wake_up(&oom_waitq);
-}
-
 void simple_lmk_mm_freed(struct mm_struct *mm)
 {
 	int i;
@@ -291,6 +285,20 @@ void simple_lmk_mm_freed(struct mm_struct *mm)
 	read_unlock(&mm_free_lock);
 }
 
+static int simple_lmk_vmpressure_cb(struct notifier_block *nb,
+				    unsigned long pressure, void *data)
+{
+	if (pressure == 100 && !atomic_cmpxchg_acquire(&needs_reclaim, 0, 1))
+		wake_up(&oom_waitq);
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block vmpressure_notif = {
+	.notifier_call = simple_lmk_vmpressure_cb,
+	.priority = INT_MAX
+};
+
 /* Initialize Simple LMK when lmkd in Android writes to the minfree parameter */
 static int simple_lmk_init_set(const char *val, const struct kernel_param *kp)
 {
@@ -301,7 +309,9 @@ static int simple_lmk_init_set(const char *val, const struct kernel_param *kp)
 		thread = kthread_run(simple_lmk_reclaim_thread, NULL,
 				     "simple_lmkd");
 		BUG_ON(IS_ERR(thread));
+		BUG_ON(vmpressure_notifier_register(&vmpressure_notif));
 	}
+
 	return 0;
 }
 

include/linux/simple_lmk.h

@@ -8,12 +8,8 @@
 struct mm_struct;
 
 #ifdef CONFIG_ANDROID_SIMPLE_LMK
-void simple_lmk_decide_reclaim(int kswapd_priority);
 void simple_lmk_mm_freed(struct mm_struct *mm);
 #else
-static inline void simple_lmk_decide_reclaim(int kswapd_priority)
-{
-}
 static inline void simple_lmk_mm_freed(struct mm_struct *mm)
 {
 }

mm/vmscan.c

@@ -50,7 +50,6 @@
 #include <linux/printk.h>
 #include <linux/dax.h>
 #include <linux/psi.h>
-#include <linux/simple_lmk.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -3625,7 +3624,6 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 		unsigned long nr_reclaimed = sc.nr_reclaimed;
 		bool raise_priority = true;
 
-		simple_lmk_decide_reclaim(sc.priority);
 		sc.reclaim_idx = classzone_idx;
 
 		/*