On Fri, Sep 27, 2024 at 07:57:49PM -0700, Yosry Ahmed wrote: > On Fri, Sep 27, 2024 at 7:16 PM Kanchana P Sridhar > <kanchana.p.sridhar@xxxxxxxxx> wrote: > > > > For zswap_store() to support large folios, we need to be able to do > > a batch update of zswap_stored_pages upon successful store of all pages > > in the folio. For this, we need to add folio_nr_pages(), which returns > > a long, to zswap_stored_pages. > > Do we really need this? A lot of places in the kernel assign the > result of folio_nr_pages() to an int (thp_nr_pages(), > split_huge_pages_all(), etc). I don't think we need to worry about > folio_nr_pages() exceeding INT_MAX for a while. You'd be surprised. Let's assume we add support for PUD-sized pages (personally I think this is too large to make sense, but some people can't be told). On arm64, we can have a 64kB page size, so that's 13 bits per level for a total of 2^26 pages per PUD. That feels uncomfortable close to 2^32 to me. Anywhere you've found that's using an int to store folio_nr_pages() is somewhere we should probably switch to long. And this, btw, is why I've moved from using an int to store folio_size() to using size_t. A PMD is already 512MB (with a 64KB page size), and so a PUD will be 4TB. thp_nr_pages() is not a good example. I'll be happy when we kill it; we're actually almost there.
