Refactor fellow_busy_region_alloc(): alloc part and commit part

src/fellow_cache.c

@@ -2174,7 +2174,7 @@ fellow_busy_obj_alloc(struct fellow_cache *fc,
 static struct buddy_off_extent *
 fellow_busy_region_alloc(struct fellow_busy *fbo, size_t size, int8_t cram)
 {
-	struct buddy_off_extent *fdr;
+	struct buddy_off_extent *fdr, reg;
 	struct fellow_cache *fc;
 
 	CHECK_OBJ_NOTNULL(fbo, FELLOW_BUSY_MAGIC);
@@ -2184,24 +2184,23 @@ fellow_busy_region_alloc(struct fellow_busy *fbo, size_t size, int8_t cram)
 	fc = fbo->fc;
 	CHECK_OBJ_NOTNULL(fc, FELLOW_CACHE_MAGIC);
 
-	assert(fbo->nregion < FCO_MAX_REGIONS);
-	fdr = &fbo->region[fbo->nregion];
-
 	if (cram)
 		FC_INJ_SZLIM(size);
 
-	*fdr = FC_INJ ? buddy_off_extent_nil :
+	reg = FC_INJ ? buddy_off_extent_nil :
 	    buddy_alloc1_off_extent_wait(fellow_dskbuddy(fc->ffd),
 	    FEP_SPC, size, cram);
 
-	if (fdr->off < 0) {
+	if (reg.off < 0) {
 		return (NULL);
 	}
 
-	AN(fdr->size);
-	AZ(fdr->size & FELLOW_BLOCK_ALIGN);
+	AN(reg.size);
+	AZ(reg.size & FELLOW_BLOCK_ALIGN);
 
-	fbo->nregion++;
+	assert(fbo->nregion < FCO_MAX_REGIONS);
+	fdr = &fbo->region[fbo->nregion++];
+	*fdr = reg;
 
 	return (fdr);
 }