[CLEANUP] fwrr: ensure that we never overflow in placements
Now we can compute the max place depending on the number of servers,
maximum weight and weight scale. The formula has been stored as a
comment so that it's easy to choose between smooth weight ramp up
and high number of servers. The default scale has been set to 16,
which permits 4000 servers with a granularity of 6% in the worst
case (weight=1).
diff --git a/include/types/backend.h b/include/types/backend.h
index e392a7b..2b35860 100644
--- a/include/types/backend.h
+++ b/include/types/backend.h
@@ -44,7 +44,16 @@
#define BE_LB_ALGO_PH (BE_LB_PROP_L7 | 0x04) /* balance on URL parameter hash */
/* various constants */
-#define BE_WEIGHT_SCALE 256 /* scale between user weight and effective weight */
+
+/* The scale factor between user weight an effective weight allows smooth
+ * weight modulation even with small weights (eg: 1). It should not be too high
+ * though because it limits the number of servers in FWRR mode in order to
+ * prevent any integer overflow. The max number of servers per backend is
+ * limited to about 2^32/255^2/scale ~= 66051/scale. A scale of 16 looks like
+ * a good value, as it allows more than 4000 servers per backend while leaving
+ * modulation steps of about 6% for servers with the lowest weight (1).
+ */
+#define BE_WEIGHT_SCALE 16
#endif /* _TYPES_BACKEND_H */