Integrate fellow_busy allocation in fellow_cache_obj_new()

It does not make sense to use up memory for busy objects if we can not
create their cache and disk counterparts in memory.

Motivated by #41

src/fellow_cache.c

@@ -1919,8 +1919,11 @@ fellow_cache_seglists_load(const struct fellow_cache *fc,
  */
 
 static struct fellow_cache_res
-fellow_cache_obj_new(struct fellow_cache *fc,
-    size_t dsk_sz, unsigned nseg_guess, uint8_t pri)
+fellow_cache_obj_new(
+    struct fellow_cache *fc,
+    size_t dsk_sz, unsigned nseg_guess,
+    struct buddy_ptr_extent *fbo_mem,
+    uint8_t pri)
 {
 	struct fellow_disk_obj *fdo;
 	struct fellow_cache_obj *fco;
@@ -1948,13 +1951,15 @@ fellow_cache_obj_new(struct fellow_cache *fc,
 	mem_sz = sizeof *fco + nseg_guess * sizeof *fcs;
 	asz = (size_t)1 << log2up(dsk_sz);
 
-	reqs = BUDDY_REQS_STK(fc->membuddy, 2);
+	reqs = BUDDY_REQS_STK(fc->membuddy, 3);
 	BUDDY_REQS_PRI(reqs, pri);
 	AN(buddy_req_page(reqs, log2up(mem_sz), 0));
 	AN(buddy_req_extent(reqs, asz, 0));
+	if (fbo_mem != NULL)
+		AN(buddy_req_extent(reqs, sizeof(struct fellow_busy), 0));
 
 	u = buddy_alloc_wait(reqs);
-	if (FC_INJ || u != 2) {
+	if (FC_INJ || u != (fbo_mem == NULL ? 2 : 3)) {
 		buddy_alloc_wait_done(reqs);
 		fcr = FCR_ALLOCFAIL("fellow_cache_obj_new alloc failed");
 		goto err;
@@ -1962,6 +1967,8 @@ fellow_cache_obj_new(struct fellow_cache *fc,
 
 	fco_mem = buddy_get_ptr_page(reqs, 0);
 	fdo_mem = buddy_get_ptr_extent(reqs, 1);
+	if (fbo_mem != NULL)
+		*fbo_mem = buddy_get_ptr_extent(reqs, 2);
 
 	buddy_alloc_wait_done(reqs);
 
@@ -2018,17 +2025,6 @@ fellow_busy_obj_alloc(struct fellow_cache *fc,
 	size_t sz, asz, dsk_sz;
 	uint16_t ldsegs;
 
-	fbo_mem = buddy_alloc1_ptr_extent_wait(fc->membuddy, FEP_NEW,
-	    sizeof *fbo, 0);
-	fbo = fbo_mem.ptr;
-	if (fbo == NULL) {
-		fcr = FCR_ALLOCFAIL("fbo_mem");
-		fellow_cache_res_check(fc, fcr);
-		return (fcr);
-	}
-	INIT_OBJ(fbo, FELLOW_BUSY_MAGIC);
-	fbo->fbo_mem = fbo_mem;
-
 	// XXX peek for known content-length=
 
 	// round up to disk block such that there
@@ -2062,15 +2058,13 @@ fellow_busy_obj_alloc(struct fellow_cache *fc,
 	if (fds_seg.off < 0) {
 		fcr = FCR_ALLOCFAIL("fds region");
 		fellow_cache_res_check(fc, fcr);
-		buddy_return1_ptr_extent(fc->membuddy, &fbo->fbo_mem);
 		return (fcr);
 	}
 
-	fcr = fellow_cache_obj_new(fc, dsk_sz, ldsegs, FEP_NEW);
+	fcr = fellow_cache_obj_new(fc, dsk_sz, ldsegs, &fbo_mem, FEP_NEW);
 	if (fcr.status != fcr_ok) {
 		fellow_cache_res_check(fc, fcr);
 		fellow_region_free(fc->ffd, &fds_seg);
-		buddy_return1_ptr_extent(fc->membuddy, &fbo->fbo_mem);
 		return (fcr);
 	}
 	fco = fcr.r.ptr;
@@ -2079,6 +2073,11 @@ fellow_busy_obj_alloc(struct fellow_cache *fc,
 	fcs = &fco->fdo_fcs;
 	CHECK_OBJ(fcs, FELLOW_CACHE_SEG_MAGIC);
 
+	fbo = fbo_mem.ptr;
+	AN(fbo);
+	INIT_OBJ(fbo, FELLOW_BUSY_MAGIC);
+	fbo->fbo_mem = fbo_mem;
+
 	// disk object in memory
 	fdo = fcs->alloc.ptr;
 	memset(fdo, 0, fcs->alloc.size);
@@ -4623,7 +4622,7 @@ fellow_cache_obj_prepread(struct fellow_cache *fc, fellow_disk_block fdba,
 	if (! PAOK(sz))
 		return (FCR_IOFAIL("bad size"));
 
-	fcr = fellow_cache_obj_new(fc, sz, 0, crit ? FEP_ITER : FEP_GET);
+	fcr = fellow_cache_obj_new(fc, sz, 0, NULL, crit ? FEP_ITER : FEP_GET);
 	if (fcr.status != fcr_ok)
 		return (fcr);