lmkd: Add new low memory kill reason

Add kill reason for a cached app kill when free memory is under low
watermark.

Bug: 306755741
Change-Id: Idf92da326f6e0990e6d9fd9acdd21b19f6bdd241
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

lmkd.cpp

@@ -2850,8 +2850,7 @@ static void mp_event_psi(int data, uint32_t events, struct polling_params *poll_
 
     /* Check if a cached app should be killed */
     if (kill_reason == NONE && wmark < WMARK_HIGH) {
-        /* TODO: introduce a new kill reason */
-        kill_reason = LOW_MEM_AND_SWAP;
+        kill_reason = LOW_MEM;
         snprintf(kill_desc, sizeof(kill_desc), "%s watermark is breached",
             wmark < WMARK_LOW ? "min" : "low");
         min_score_adj = PREVIOUS_APP_ADJ + 1;

statslog.h

@@ -64,6 +64,7 @@ enum kill_reasons {
     DIRECT_RECL_AND_THRASHING,
     LOW_MEM_AND_SWAP_UTIL,
     LOW_FILECACHE_AFTER_THRASHING,
+    LOW_MEM,
     KILL_REASON_COUNT
 };