Free strings objects instead of dismissing

Instead of dismissing with madvise(MADV_DONTNEED) we free it via the
allocator. This has advantage that it allows the allocator to
accumulate free buffers to free whole pages. While madvise is nop
if the buffer is less than a page. The allocator overhead is
minimal, because raw strings (sds) use the fast path.

Signed-off-by: Vadym Khoptynets <vadymkh@amazon.com>

src/object.c

@@ -394,11 +394,14 @@ void dismissSds(sds s) {
     dismissMemory(sdsAllocPtr(s), sdsAllocSize(s));
 }
 
-/* See dismissObject() */
+/* See dismissObject(). String object is an exception. Instead of
+ * dismissing it with madvise(MADV_DONTNEED) we free it via the
+ * allocator. This has advantage that it allows the allocator to
+ * accumulate free buffers to free whole pages. While madvise is nop
+ * if the buffer is less than a page. The allocator overhead is
+ * minimal, because raw strings (sds) use the fast path. */
 void dismissStringObject(robj *o) {
-    if (o->encoding == OBJ_ENCODING_RAW) {
-        dismissSds(o->ptr);
-    }
+    freeStringObject(o);
 }
 
 /* See dismissObject() */