kernel: Start clearing caches when free memory is lower than 1MiB

This is done to avoid returning ENOMEM errors when cache memory can still be reclaimed.

kernel/src/memory/MemoryManager.cpp

@@ -157,6 +157,13 @@ namespace MemoryManager
         used_mem += ARCH_PAGE_SIZE;
         free_mem -= ARCH_PAGE_SIZE;
 
+        if (free_mem < 1024 * 1024)
+        {
+            // Less than 1 MiB of free memory! Let's start clearing caches...
+            kwarnln("Less than 1 MiB of free memory, clearing caches to try to gain extra memory");
+            Scheduler::signal_oom_thread();
+        }
+
         return index * ARCH_PAGE_SIZE;
     }