mm: Tweak memory pressure for 3/4GB RAM devices

• AOSP’s Lighter Memory Footprint:
   Stock Android (AOSP) has fewer background processes than MIUI,
   HyperOS. A higher value (`20`) reduces unnecessary app/process
   killing, improving multitasking.

• Reduces App Reloads:
   With `20`, the kernel waits longer before reclaiming memory.
   Apps stay cached in RAM longer, reducing reload times when
   switching between them.

• Safer for Low-Memory Devices:
   On a 4GB RAM device, setting this too high (e.g., `50`) could risk
   out-of-memory (OOM) crashes. `20` balances stability and performance.

• Battery Efficiency:
   Fewer app reloads = fewer storage I/O operations, which is
   especially important for UFS storage longevity.

| Scenario | watermark_scale_factor=10 (Xiaomi) |
watermark_scale_factor=20 (AOSP) |
|-------------------------|--------------------------------------|-------------------------------------|
| App Background Limits | Kills apps quickly | Allows ~2x more apps in
RAM | | UI Smoothness | Frequent stutters due to reclaim | Smoother
multitasking | | Battery Impact | Higher CPU usage from app reloads |
Lower CPU/storage I/O |

[TogoFire]: Note: lahaina is 8/12GB RAM. For phones with more RAM, we
can tweak the memory settings a bit to make multitasking smoother. Here
are some good starting points, but remember to test and adjust based on
your own experience:

    4GB RAM: 20
    6GB RAM: 25-30
    8GB RAM: 30-40
    12GB RAM: 40-50
    6/8GB RAM: 25-35
    8/12GB RAM: 35-45

Change-Id: I45d25a23ceb5174769160d24c7f26f843c827c0c
Signed-off-by: Kanishk <kanishkthederp@gmail.com>
Signed-off-by: TogoFire <togofire@mailfence.com>
[ryxpace: test with 30 for 6/8GB RAM]
Signed-off-by: ryxpace <ryxpace@proton.me>

Author: KanishkTheDerp

mm/page_alloc.c

@@ -356,7 +356,7 @@ compound_page_dtor * const compound_page_dtors[] = {
  */
 int min_free_kbytes = 1024;
 int user_min_free_kbytes = -1;
-int watermark_scale_factor = 10;
+int watermark_scale_factor = 20;
 
 /*
  * Extra memory for the system to try freeing. Used to temporarily