Support camming of segment memory allocation

adjust dsk size if mem allocation was smaller than requested

src/fellow_cache.c

@@ -2039,6 +2039,39 @@ fellow_busy_body_seg_alloc(struct fellow_busy *fbo,
 	return (want);
 }
 
+// adjust fds size to fcs size
+static void
+fellow_busy_body_seg_adjust(struct fellow_busy *fbo,
+    const struct fellow_cache_seg *fcs)
+{
+	struct fellow_body_region *fbr;
+	struct buddy_off_extent *fdr;
+	struct fellow_disk_seg *fds;
+	size_t surplus;
+
+	CHECK_OBJ_NOTNULL(fbo, FELLOW_BUSY_MAGIC);
+	CHECK_OBJ_NOTNULL(fcs, FELLOW_CACHE_SEG_MAGIC);
+	fds = fcs->disk_seg;
+	CHECK_OBJ_NOTNULL(fds, FELLOW_DISK_SEG_MAGIC);
+
+	if (fcs->alloc.size == fds->seg.size)
+		return;
+
+	AN(fds->seg.off);
+	AN(fds->seg.size);
+
+	assert(fds->seg.size > fcs->alloc.size);
+	surplus = fds->seg.size - fcs->alloc.size;
+	assert((surplus & FELLOW_BLOCK_ALIGN) == 0);
+
+	fbr = &fbo->body_region;
+	fdr = fbr->reg;
+	AN(fdr);
+
+	assert(fbr->len >= surplus);
+	fbr->len -= surplus;
+}
+
 /* return an fds to the body seg (for failed memalloc) */
 static void
 fellow_busy_body_seg_return(struct fellow_busy *fbo,
@@ -3432,7 +3465,7 @@ fellow_busy_body_seg_next(struct fellow_busy *fbo)
  * used for body and auxattr
  */
 static size_t fellow_busy_seg_memalloc(buddy_t *membuddy,
-    struct fellow_cache_seg *fcs)
+    struct fellow_cache_seg *fcs, int8_t cram)
 {
 	struct fellow_disk_seg *fds;
 
@@ -3448,15 +3481,19 @@ static size_t fellow_busy_seg_memalloc(buddy_t *membuddy,
 	AZ(fcs->alloc.size);
 
 	fcs->alloc = buddy_alloc1_ptr_extent_wait(membuddy, FEP_SPC,
-	    fds->seg.size, 0);
+	    fds->seg.size, cram);
 
 	if (fcs->alloc.ptr == NULL)
 		return (0);
 
+	// cram needs to be chosen correctly
+	assert(fcs->alloc.size >= MIN_FELLOW_BLOCK);
+	assert((fcs->alloc.size & FELLOW_BLOCK_ALIGN) == 0);
+	// membuddy min < dskbuddy min
+	assert(fcs->alloc.size <= fds->seg.size);
+
 	memset(fcs->alloc.ptr, 0, fcs->alloc.size);
 
-	// membuddy min < dskbuddy min
-	assert(fds->seg.size == fcs->alloc.size);
 	AZ(fcs->refcnt);
 	fcs->refcnt = 1;
 	fellow_cache_seg_transition_locked_notincore(fcs, FCS_BUSY);
@@ -3489,7 +3526,7 @@ fellow_busy_seg_alloc(struct fellow_busy *fbo,
 	if (fdr == NULL)
 		return (0);
 	fds->seg = *fdr;
-	if (fellow_busy_seg_memalloc(fbo->fc->membuddy, fcs) == 0)
+	if (fellow_busy_seg_memalloc(fbo->fc->membuddy, fcs, 0) == 0)
 		// we do not need to free because we use the busy region
 		return (0);
 	return (1);
@@ -3577,12 +3614,16 @@ fellow_busy_obj_getspace(struct fellow_busy *fbo, size_t *sz, uint8_t **ptr)
 		goto out;
 	}
 
-	spc = fellow_busy_seg_memalloc(fbo->fc->membuddy, fcs);
+	spc = fellow_busy_seg_memalloc(fbo->fc->membuddy, fcs,
+	    buddy_cramlimit_bits(spc, fbo->fc->tune->cram, MIN_FELLOW_BITS));
 	if (spc == 0) {
 		fellow_busy_body_seg_return(fbo, fcs->disk_seg);
 		fcr = FCR_ALLOCFAIL("body memory seg alloc");
 		goto out;
 	}
+	// reduce fds size if fcs alloc crammed
+	fellow_busy_body_seg_adjust(fbo, fcs);
+
 	assert(fcs->state == FCS_BUSY);
 	fbo->body_seglist->fdsl->nsegs++;
 	assert(fbo->body_seglist->fdsl->nsegs <= fbo->body_seglist->lsegs);