Refactor out the segment sizing strategy

src/fellow_cache.c

@@ -2365,6 +2365,58 @@ fellow_disk_seglist_alloc(struct fellow_busy *fbo,
 	return (FCR_OK(fcsl));
 }
 
+struct szc {
+	size_t sz;
+	int8_t cram;
+};
+
+/*
+ * Return a size to allocate next for the object body,
+ * given that already bytes are alocated
+ */
+static struct szc
+fellow_busy_body_size_strategy(const struct fellow_busy *fbo, size_t already)
+{
+	unsigned chunkbits;
+	struct szc szc;
+
+	chunkbits = fbo->fc->tune->chunk_exponent;
+	szc.cram = fbo->fc->tune->cram;
+
+	assert(fbo->sz_estimate > already);
+	szc.sz = fbo->sz_estimate - fbo->sz_dskalloc;
+
+	// out of regions: no cram
+	// if also grown: assume worst case size
+	if (fbo->nregion >= FCO_MAX_REGIONS - FCO_REGIONS_RESERVE) {
+		szc.cram = 0;
+
+		if (fbo->grown) {
+			szc.sz = fbo->fc->tune->objsize_max -
+			    fbo->sz_dskalloc;
+		}
+	}
+	else if (fbo->grown == 0 && (szc.sz >> chunkbits) == 0)
+		// c-l or initial chunked - keep small req
+		(void)szc.sz;
+	else if (fbo->grown == 0)
+		// known size -> round down
+		szc.sz = (size_t)1 << log2down(szc.sz);
+	else
+		// size unknown -> round up
+		szc.sz = (size_t)1 << log2up(szc.sz);
+
+	/* for allocation larger than chunk size, always allow cram down to
+	 * chunk size, but do split pages (INT8_MIN)
+	 */
+	if (szc.cram > 0 && szc.sz >= (size_t)1 << chunkbits) {
+		assert(chunkbits <= INT8_MAX);
+		szc.cram = buddy_cramlimit_bits(szc.sz, INT8_MIN,
+		    (int8_t)chunkbits);
+	}
+	return (szc);
+}
+
 /* allocate a new region for body data */
 static size_t
 fellow_busy_body_seg_alloc(struct fellow_busy *fbo,
@@ -2373,9 +2425,8 @@ fellow_busy_body_seg_alloc(struct fellow_busy *fbo,
 	struct fellow_body_region *fbr;
 	struct buddy_off_extent *fdr;
 	struct fellow_cache *fc;
-	unsigned chunkbits;
+	struct szc szc;
 	size_t spc;
-	int8_t cram;
 
 	CHECK_OBJ_NOTNULL(fbo, FELLOW_BUSY_MAGIC);
 	CHECK_OBJ_NOTNULL(fds, FELLOW_DISK_SEG_MAGIC);
@@ -2389,43 +2440,13 @@ fellow_busy_body_seg_alloc(struct fellow_busy *fbo,
 
 	fdr = fbr->reg;
 	if (fdr == NULL || fbr->len == fdr->size) {
-		cram = fbo->fc->tune->cram;
-		chunkbits = fbo->fc->tune->chunk_exponent;
 
 		memset(fbr, 0, sizeof *fbr);
 
 		assert(fbo->sz_estimate > fbo->sz_dskalloc);
-		spc = fbo->sz_estimate - fbo->sz_dskalloc;
-
-		if (fbo->nregion >= FCO_MAX_REGIONS - FCO_REGIONS_RESERVE) {
-			// out of regions: no cram,
-			// if grown, assume worst, else keep spc
-			cram = 0;
-			if (fbo->grown) {
-				spc = fbo->fc->tune->objsize_max -
-				    fbo->sz_dskalloc;
-			}
-		}
-		else if (fbo->grown == 0 && (spc >> chunkbits) == 0)
-			// c-l or initial chunked - keep small req
-			(void)spc;
-		else if (fbo->grown == 0)
-			// known size -> round down
-			spc = (size_t)1 << log2down(spc);
-		else
-			// size unknown -> round up
-			spc = (size_t)1 << log2up(spc);
-
-		/* for allocation larger than chunk size, always allow
-		 * cram down to chunk size, but do split pages (INT8_MIN)
-		 */
-		if (cram > 0 && spc >= (size_t)1 << chunkbits) {
-			assert(fbo->fc->tune->chunk_exponent <= INT8_MAX);
-			cram = buddy_cramlimit_bits(spc, INT8_MIN,
-			    (int8_t)fbo->fc->tune->chunk_exponent);
-		}
+		szc = fellow_busy_body_size_strategy(fbo, fbo->sz_dskalloc);
 
-		fdr = fellow_busy_region_alloc(fbo, spc, cram);
+		fdr = fellow_busy_region_alloc(fbo, szc.sz, szc.cram);
 		if (fdr == NULL)
 			return (0);