PGO_OVERWRITE
const bool overwrite = (flags & PGO_OVERWRITE) != 0;
pagerflags |= PGO_OVERWRITE;
bool overwrite = ((flags & PGO_OVERWRITE) != 0);
PGO_SYNCIO|PGO_OVERWRITE|PGO_PASTEOF|PGO_NOBLOCKALLOC|
gpflags |= PGO_OVERWRITE | PGO_NOBLOCKALLOC;
KASSERT((pg->flags & PG_FAKE) == 0 || (gpflags & PGO_OVERWRITE));