mm/vmscan: add pgrotate_anon and pgrotate_file vmstat counters

Reclaim can spend substantial work on an LRU type without immediately
reclaiming or demoting a corresponding amount of memory.  Record this work
in PGROTATE_ANON and PGROTATE_FILE.

For classic LRU reclaim:

  - Inactive-list reclaim adds nr_scanned - nr_reclaimed to the
    corresponding anon/file counter when isolation succeeds.
  - Active-list reclaim adds referenced executable file folios that
    are retained on the active list to PGROTATE_FILE. Active anon
    reclaim does not contribute this component.

For MGLRU, add the number of initially isolated pages that remain
unreclaimed after both the initial and retry passes to the counter for the
selected anon/file type.

These counters are distinct from the existing pgrotated vm event. 
pgrotated records an actual move to the inactive-list tail, primarily
after reclaim-marked writeback completes or failed invalidation leaves a
folio for accelerated reclaim.  PGROTATE_ANON and PGROTATE_FILE measure
reclaim cost and do not imply that a folio moved to an LRU tail.

A subsequent patch will consume these counters for anon/file scan
balancing.

Link: https://lore.kernel.org/20260727162550.2032-3-usama.arif@linux.dev
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0507193b3ae3..1cc5ea506b7c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -323,6 +323,8 @@ enum node_stat_item {
 	PGSCAN_PROACTIVE,
 	PGSCAN_ANON,
 	PGSCAN_FILE,
+	PGROTATE_ANON,
+	PGROTATE_FILE,
 	PGREFILL,
 #ifdef CONFIG_HUGETLB_PAGE
 	NR_HUGETLB,