BTT_PG_SIZE
if (available % BTT_PG_SIZE)
available -= (available % BTT_PG_SIZE);
available -= 2 * BTT_PG_SIZE;
logsize = roundup(arena->nfree * LOG_GRP_SIZE, BTT_PG_SIZE);
arena->internal_nlba = div_u64(available - BTT_PG_SIZE,
mapsize = roundup((arena->external_nlba * MAP_ENT_SIZE), BTT_PG_SIZE);
arena->dataoff = arena->infooff + BTT_PG_SIZE;
: (arena->info2off - arena->infooff + BTT_PG_SIZE);