+void returnMemoryToOS(nat n /* megablocks */)
+{
+ static bdescr *bd;
+ nat size;
+
+ bd = free_mblock_list;
+ while ((n > 0) && (bd != NULL)) {
+ size = BLOCKS_TO_MBLOCKS(bd->blocks);
+ if (size > n) {
+ nat newSize = size - n;
+ char *freeAddr = MBLOCK_ROUND_DOWN(bd->start);
+ freeAddr += newSize * MBLOCK_SIZE;
+ bd->blocks = MBLOCK_GROUP_BLOCKS(newSize);
+ freeMBlocks(freeAddr, n);
+ n = 0;
+ }
+ else {
+ char *freeAddr = MBLOCK_ROUND_DOWN(bd->start);
+ n -= size;
+ bd = bd->link;
+ freeMBlocks(freeAddr, size);
+ }
+ }
+ free_mblock_list = bd;
+
+ osReleaseFreeMemory();
+
+ IF_DEBUG(gc,
+ if (n != 0) {
+ debugBelch("Wanted to free %d more MBlocks than are freeable\n",
+ n);
+ }
+ );
+}
+