Refactor region reserve

src/fellow_cache.c

@@ -598,6 +598,8 @@ struct fellow_busy {
 	struct fellow_body_region	body_region;
 
 #define FCO_MAX_REGIONS ((FELLOW_DISK_LOG_BLOCK_ENTRIES - 1) * DLE_REG_NREGION)
+// for fdsl and busy region last chance
+#define FCO_REGIONS_RESERVE 3
 	struct buddy_off_extent	region[FCO_MAX_REGIONS];
 	unsigned			nregion;
 	uint8_t				grown;
@@ -1839,8 +1841,8 @@ fellow_busy_region_alloc(struct fellow_busy *fbo, size_t size, int8_t cram)
 	fc = fbo->fc;
 	CHECK_OBJ_NOTNULL(fc, FELLOW_CACHE_MAGIC);
 
-	/* stop cramming if we used half the regions already */
-	if (fbo->nregion < FCO_MAX_REGIONS / 2)
+	/* stop cramming if we run out of regions */
+	if (fbo->nregion < FCO_MAX_REGIONS - FCO_REGIONS_RESERVE)
 		cram = 0;
 
 	assert(fbo->nregion < FCO_MAX_REGIONS);