pack: increase buffer reallocation for higher performance (fix #8492)

When converting from msgpack to raw JSON or sds-json, the reallocation
strategy is very convervative to keep the memory usage very low, but
in most of scenarios this lead to more fragmentation and high CPU
usage.

This patch changes the memory reallocation with an exponential
strategy for better performance.

Kudos to @LukasJerabek and @lecaros for helping to troubleshoot and
indentify the root cause of this issue.

Signed-off-by: Eduardo Silva <[email protected]>

src/flb_pack.c

@@ -807,10 +807,11 @@ flb_sds_t flb_msgpack_raw_to_json_sds(const void *in_buf, size_t in_size)
     while (1) {
         ret = flb_msgpack_to_json(out_buf, out_size, root);
         if (ret <= 0) {
+            realloc_size *= 2;
             tmp_buf = flb_sds_increase(out_buf, realloc_size);
             if (tmp_buf) {
                 out_buf = tmp_buf;
-                out_size += realloc_size;
+                out_size *= realloc_size;
             }
             else {
                 flb_errno();
@@ -1168,7 +1169,7 @@ char *flb_msgpack_to_json_str(size_t size, const msgpack_object *obj)
         ret = flb_msgpack_to_json(buf, size, obj);
         if (ret <= 0) {
             /* buffer is small. retry.*/
-            size += 128;
+            size *= 2;
             tmp = flb_realloc(buf, size);
             if (tmp) {
                 buf = tmp;