vmscan: add a vmscan event for reclaim_pages

reclaim_folio_list uses a dummy reclaim_stat and is not being used. To
know the memory stat, add a new trace event. This is useful how how many
pages are not reclaimed or why.

This is an example:

mm_vmscan_reclaim_pages: nid=0 nr_scanned=112 nr_reclaimed=112 nr_dirty=0 nr_writeback=0 nr_congested=0 nr_immediate=0 nr_activate_anon=0 nr_activate_file=0 nr_ref_keep=0 nr_unmap_fail=0

Currently reclaim_folio_list is only called by reclaim_pages, and
reclaim_pages is used by damon and madvise. In the latest Android,
reclaim_pages is also used by shmem to reclaim all pages in a
address_space.

[[e-mail]: use sc.nr_scanned rather than new counting]
Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Jaewon Kim <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Cc: Jaewon Kim <[e-mail]>
Cc: Kalesh Singh <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: SeongJae Park <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/trace/events/vmscan.h

···
 		show_reclaim_flags(__entry->reclaim_flags))
 );
 
+TRACE_EVENT(mm_vmscan_reclaim_pages,
+
+	TP_PROTO(int nid,
+		unsigned long nr_scanned, unsigned long nr_reclaimed,
+		struct reclaim_stat *stat),
+
+	TP_ARGS(nid, nr_scanned, nr_reclaimed, stat),
+
+	TP_STRUCT__entry(
+		__field(int, nid)
+		__field(unsigned long, nr_scanned)
+		__field(unsigned long, nr_reclaimed)
+		__field(unsigned long, nr_dirty)
+		__field(unsigned long, nr_writeback)
+		__field(unsigned long, nr_congested)
+		__field(unsigned long, nr_immediate)
+		__field(unsigned int, nr_activate0)
+		__field(unsigned int, nr_activate1)
+		__field(unsigned long, nr_ref_keep)
+		__field(unsigned long, nr_unmap_fail)
+	),
+
+	TP_fast_assign(
+		__entry->nid = nid;
+		__entry->nr_scanned = nr_scanned;
+		__entry->nr_reclaimed = nr_reclaimed;
+		__entry->nr_dirty = stat->nr_dirty;
+		__entry->nr_writeback = stat->nr_writeback;
+		__entry->nr_congested = stat->nr_congested;
+		__entry->nr_immediate = stat->nr_immediate;
+		__entry->nr_activate0 = stat->nr_activate[0];
+		__entry->nr_activate1 = stat->nr_activate[1];
+		__entry->nr_ref_keep = stat->nr_ref_keep;
+		__entry->nr_unmap_fail = stat->nr_unmap_fail;
+	),
+
+	TP_printk("nid=%d nr_scanned=%ld nr_reclaimed=%ld nr_dirty=%ld nr_writeback=%ld nr_congested=%ld nr_immediate=%ld nr_activate_anon=%d nr_activate_file=%d nr_ref_keep=%ld nr_unmap_fail=%ld",
+		__entry->nid,
+		__entry->nr_scanned, __entry->nr_reclaimed,
+		__entry->nr_dirty, __entry->nr_writeback,
+		__entry->nr_congested, __entry->nr_immediate,
+		__entry->nr_activate0, __entry->nr_activate1,
+		__entry->nr_ref_keep, __entry->nr_unmap_fail)
+);
+
 TRACE_EVENT(mm_vmscan_lru_shrink_inactive,
 
 	TP_PROTO(int nid,

mm/vmscan.c

···
 static unsigned int reclaim_folio_list(struct list_head *folio_list,
 				      struct pglist_data *pgdat)
 {
-	struct reclaim_stat dummy_stat;
+	struct reclaim_stat stat;
 	unsigned int nr_reclaimed;
 	struct folio *folio;
 	struct scan_control sc = {
···
 		.no_demotion = 1,
 	};
 
-	nr_reclaimed = shrink_folio_list(folio_list, pgdat, &sc, &dummy_stat, true);
+	nr_reclaimed = shrink_folio_list(folio_list, pgdat, &sc, &stat, true);
 	while (!list_empty(folio_list)) {
 		folio = lru_to_folio(folio_list);
 		list_del(&folio->lru);
 		folio_putback_lru(folio);
 	}
+	trace_mm_vmscan_reclaim_pages(pgdat->node_id, sc.nr_scanned, nr_reclaimed, &stat);
 
 	return nr_reclaimed;
 }