Bring struct fellow_busy below 4KB

Closes #16

src/fellow_cache.c

@@ -468,6 +468,10 @@ struct fellow_busy {
 	unsigned			magic;
 #define FELLOW_BUSY_MAGIC		0x8504a132
 
+	// for fellow_busy_setattr()
+	uint32_t			va_data_len;
+	uint8_t				*va_data;
+
 	struct buddy_ptr_extent	fbo_mem;
 	size_t				sz_estimate;
 
@@ -489,15 +493,11 @@ struct fellow_busy {
 	struct buddy_off_extent	region[FCO_MAX_REGIONS];
 	unsigned			nregion;
 
+#define FBO_NIO 11
 	/* protected by fco mtx */
 	uint8_t				io_idx;
 	uint8_t				io_outstanding;
-#define FBO_NIO FCO_MAX_REGIONS
 	struct fellow_busy_io		io[FBO_NIO];
-
-	// for fellow_busy_setattr()
-	uint32_t			va_data_len;
-	uint8_t			*va_data;
 };
 
 struct fellow_cache {
@@ -5014,6 +5014,9 @@ main(int argc, char **argv)
 {
 	unsigned l, hash;
 
+	DBG("fellow_busy %zu", sizeof(struct fellow_busy));
+	assert(sizeof(struct fellow_busy) <= MIN_FELLOW_BLOCK);
+
 #ifdef HAVE_XXHASH_H
 	l = FH_LIM;
 #else