[host_memory] decrease latency of mapping on linux (#232)

Signed-off-by: lizzie <lizzie@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/232
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: Shinmegumi <shinmegumi@eden-emu.dev>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

src/common/host_memory.cpp

@@ -598,12 +598,17 @@ public:
 
     bool ClearBackingRegion(size_t physical_offset, size_t length) {
 #ifdef __linux__
+        // Only incur syscall cost IF memset would be slower (theshold = 16MiB)
+        // TODO(lizzie): Smarter way to dynamically get this threshold (broadwell != raptor lake) for example
+        if (length >= 2097152UL * 8) {
             // Set MADV_REMOVE on backing map to destroy it instantly.
             // This also deletes the area from the backing file.
             int ret = madvise(backing_base + physical_offset, length, MADV_REMOVE);
             ASSERT_MSG(ret == 0, "madvise failed: {}", strerror(errno));
-
             return true;
+        } else {
+            return false;
+        }
 #else
         return false;
 #endif