On Wed, Jun 30, 2021 at 10:30:38AM +0200, Michal Hocko wrote:

quoted

-	if (PageAnon(page)) {
-		if (page_mapped(page)) {
+	if (folio_anon(folio)) {
+		if (folio_mapped(folio)) {
 			__mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
 			__mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
-			if (PageTransHuge(page)) {
+			if (folio_multi(folio)) {

Shouldn't be folio_transhuge? The resulting code is the same but
folio_transhuge is more explicit and matches the THP aspect.

I genuinely don't know.  For the benefit of those reading along, the
important part of the context is:

                if (folio_mapped(folio)) {
                        __mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
                        __mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
                        if (folio_multi(folio)) {
                                __mod_lruvec_state(from_vec, NR_ANON_THPS,
                                                   -nr_pages);
                                __mod_lruvec_state(to_vec, NR_ANON_THPS,
                                                   nr_pages);
                        }
                }

We need to decide what 'NR_ANON_THPS' means in a folio-based world where
we have folios of all orders.  Does it count only the number of pages
in folios >= HPAGE_PMD_SIZE?  Or does it count the number of pages in
folios > PAGE_SIZE?

Similar question (and I suspect the same answer) for NR_SHMEM_THPS and
NR_FILE_THPS.  Right now, I've been accounting any multi-page folio as
a THP, but I don't have a good sense of what the answer should be.