Re: [PATCH v4 1/2] mm: count the number of anonymous THPs per size

[chunpeng lee <chunpeng.lee@outlook.com>]

> Let's track for each anonymous THP size, how many of them are currently
> allocated. We'll track the complete lifespan of an anon THP, starting
> when it becomes an anon THP ("large anon folio") (->mapping gets set),
> until it gets freed (->mapping gets cleared).

IIUC, If an anon THP is swapped out as a whole, it is still being counted, correct?

> Note that AnonPages in /proc/meminfo currently tracks the total number
> of *mapped* anonymous *pages*, and therefore has slightly different
> semantics. In the future, we might also want to track "nr_anon_mapped"
> for each THP size, which might be helpful when comparing it to the
> number of allocated anon THPs (long-term pinning, stuck in swapcache,
> memory leaks, ...).

If we do not consider tracking each THP size, Can we expand the NR_ANON_THPS
statistic to include pte-mapped thp as well?

---
 mm/memcontrol-v1.c | 2 +-
 mm/rmap.c | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index 44803cbea38a..3e44175db81f 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -786,7 +786,7 @@ static int mem_cgroup_move_account(struct folio *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 (folio_test_pmd_mappable(folio)) {
+ if (folio_test_large(folio)) {
 __mod_lruvec_state(from_vec, NR_ANON_THPS,
 -nr_pages);
 __mod_lruvec_state(to_vec, NR_ANON_THPS,
diff --git a/mm/rmap.c b/mm/rmap.c
index a8797d1b3d49..97eb25d023ba 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1291,6 +1291,11 @@ static void __folio_mod_stat(struct folio *folio, int nr, int nr_pmdmapped)
 if (nr) {
 idx = folio_test_anon(folio) ? NR_ANON_MAPPED : NR_FILE_MAPPED;
 __lruvec_stat_mod_folio(folio, idx, nr);
+
+ if (folio_test_anon(folio) &&
+ folio_test_large(folio) &&
+ nr == 1 << folio_order(folio))
+ __lruvec_stat_mod_folio(folio, NR_ANON_THPS, nr);
 }
 if (nr_pmdmapped) {
 if (folio_test_anon(folio)) {
--