Add absolute condition to Mem alerts

Change-Id: Ibcca517d9c46ab900dc6c9503e2e850206093a3f
PROD-Related: PROD-29223
diff --git a/linux/meta/prometheus.yml b/linux/meta/prometheus.yml
index ecf28c3..32db6bc 100644
--- a/linux/meta/prometheus.yml
+++ b/linux/meta/prometheus.yml
@@ -190,31 +190,29 @@
         description: "The {{ $labels.device }} disk on the {{ $labels.host }} node has {{ $value }} 'end-to-end' errors."
     {%- endraw %}
   {%- endif %}
+    {%- raw %}
     SystemMemoryFullWarning:
-      {%- set mem_threshold = monitoring.memory_usage_percentage.warn|float %}
       if: >-
-        mem_used_percent >= {{ mem_threshold }}
+        mem_used_percent > 90 and mem_available < 8 * 2^30
       for: 2m
       labels:
         severity: warning
         service: system
       annotations:
-        summary: "{{ mem_threshold }}{%- raw %}% of memory is used"
+        summary: "More than 90% of memory is used or less than 8 GB of memory is available"
         description: "The {{ $labels.host }} node uses {{ $value }}% of memory for 2 minutes."
     SystemMemoryFullMajor:
-      {%- endraw %}
-      {%- set mem_threshold = monitoring.memory_usage_percentage.major|float %}
       if: >-
-        mem_used_percent >= {{ mem_threshold }}
+        mem_used_percent > 95 and mem_available < 4 * 2^30
       for: 2m
       labels:
         severity: major
         service: system
       annotations:
-        summary: "{{ mem_threshold }}{%- raw %}% of memory is used"
+        summary: "More than 95% of memory is used or less than 4 GB of memory is available"
         description: "The {{ $labels.host }} node uses {{ $value }}% of memory for 2 minutes."
     SystemRxPacketsDroppedTooHigh:
-      {%- endraw %}
+    {%- endraw %}
       {%- set net_rx_dropped_threshold = monitoring.rx_packets_dropped_threshold.warn %}
       if: >-
         increase(net_drop_in[1m]) > {{ net_rx_dropped_threshold }} unless on (host,interface) bond_slave_active == 0