On Mon, Jun 14, 2021 at 12:45:34PM +0100, David Howells wrote: > Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > > Why not: > > > > > > if (page_offset(page) >= i_size) > > > > > > > That doesn't handle THP's correctly. It's just a PAGE_SIZE shift. > > I asked Willy about that one and he said it will. Now, granted, the code > doesn't seem to do that, but possibly he has a patch for it? a THP has its index in units of PAGE_SIZE. If you have an order-4 page at file offset 32 * PAGE_SIZE, it will have page->index set to 32. So shifting by PAGE_SIZE is correct. This contrasts with the insanity of hugetlbfs which has its index in units of the hpage_size. The only thing is that you have to pass around the head page. tail->index is meaningless. But you should always be passing around the head page unless there's a really good reason not to (eg vmf->page where we really need to know which subpage the fault was in).
