[PATCH v2] vmscan: add a vmscan event for reclaim_pages

The 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

Currenlty 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.

Signed-off-by: Jaewon Kim <redacted>
---
v2: remove reclaim_stat_add function and call the trace on each node
v1: introduce a new trace event
---
 include/trace/events/vmscan.h | 45 +++++++++++++++++++++++++++++++++++
 mm/vmscan.c                   | 16 +++++++++----
 2 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 1a488c30afa5..490958fa10de 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h

@@ -346,6 +346,51 @@ TRACE_EVENT(mm_vmscan_write_folio,
 		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,

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 749cdc110c74..0c2c36bf4c5a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -2126,9 +2126,10 @@ static void shrink_active_list(unsigned long nr_to_scan,
 }
 
 static unsigned int reclaim_folio_list(struct list_head *folio_list,
+				      unsigned int nr_scanned,
 				      struct pglist_data *pgdat)
 {
-	struct reclaim_stat dummy_stat;
+	struct reclaim_stat stat;
 	unsigned int nr_reclaimed;
 	struct folio *folio;
 	struct scan_control sc = {

@@ -2139,12 +2140,13 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list,
 		.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, nr_scanned, nr_reclaimed, &stat);
 
 	return nr_reclaimed;
 }

@@ -2152,6 +2154,7 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list,
 unsigned long reclaim_pages(struct list_head *folio_list)
 {
 	int nid;
+	unsigned int nr_scanned = 0;
 	unsigned int nr_reclaimed = 0;
 	LIST_HEAD(node_folio_list);
 	unsigned int noreclaim_flag;

@@ -2168,15 +2171,18 @@ unsigned long reclaim_pages(struct list_head *folio_list)
 		if (nid == folio_nid(folio)) {
 			folio_clear_active(folio);
 			list_move(&folio->lru, &node_folio_list);
+			nr_scanned += folio_nr_pages(folio);
 			continue;
 		}
 
-		nr_reclaimed += reclaim_folio_list(&node_folio_list, NODE_DATA(nid));
+		nr_reclaimed += reclaim_folio_list(&node_folio_list, nr_scanned,
+						   NODE_DATA(nid));
+		nr_scanned = 0;
 		nid = folio_nid(lru_to_folio(folio_list));
 	} while (!list_empty(folio_list));
 
-	nr_reclaimed += reclaim_folio_list(&node_folio_list, NODE_DATA(nid));
-
+	nr_reclaimed += reclaim_folio_list(&node_folio_list, nr_scanned,
+					   NODE_DATA(nid));
 	memalloc_noreclaim_restore(noreclaim_flag);
 
 	return nr_reclaimed;

-- 
2.25.1

On 10/11/24 14:49, Jaewon Kim wrote:

Why is the new calculation of nr_scanned needed? Could you just take a delta
of sc->nr_scanned, i.e. after - before calling shrink_folio_list() ?

On 10/11/24 14:49, Jaewon Kim wrote:

quoted

The 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

Currenlty 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.

Signed-off-by: Jaewon Kim <redacted>
---
v2: remove reclaim_stat_add function and call the trace on each node
v1: introduce a new trace event
---
 include/trace/events/vmscan.h | 45 +++++++++++++++++++++++++++++++++++
 mm/vmscan.c                   | 16 +++++++++----
 2 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 1a488c30afa5..490958fa10de 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h

@@ -346,6 +346,51 @@ TRACE_EVENT(mm_vmscan_write_folio,
 		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,

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 749cdc110c74..0c2c36bf4c5a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -2126,9 +2126,10 @@ static void shrink_active_list(unsigned long nr_to_scan,
 }
 
 static unsigned int reclaim_folio_list(struct list_head *folio_list,
+				      unsigned int nr_scanned,
 				      struct pglist_data *pgdat)
 {
-	struct reclaim_stat dummy_stat;
+	struct reclaim_stat stat;
 	unsigned int nr_reclaimed;
 	struct folio *folio;
 	struct scan_control sc = {

@@ -2139,12 +2140,13 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list,
 		.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, nr_scanned, nr_reclaimed, &stat);

Why is the new calculation of nr_scanned needed? Could you just take a delta
of sc->nr_scanned, i.e. after - before calling shrink_folio_list() ?

Oh correct. 

Except the case of (!folio_trylock(folio)), shrink_folio_list would count at sc->nr_scanned.
I don't understand why we do not count this lock case though.

Let me try to change as you suggested.
I think without 'after - before', we can just use sc->nr_scanned after shrink_folio_list.

Thank you

quoted

 
 	return nr_reclaimed;
 }

@@ -2152,6 +2154,7 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list,
 unsigned long reclaim_pages(struct list_head *folio_list)
 {
 	int nid;
+	unsigned int nr_scanned = 0;
 	unsigned int nr_reclaimed = 0;
 	LIST_HEAD(node_folio_list);
 	unsigned int noreclaim_flag;

@@ -2168,15 +2171,18 @@ unsigned long reclaim_pages(struct list_head *folio_list)
 		if (nid == folio_nid(folio)) {
 			folio_clear_active(folio);
 			list_move(&folio->lru, &node_folio_list);
+			nr_scanned += folio_nr_pages(folio);
 			continue;
 		}
 
-		nr_reclaimed += reclaim_folio_list(&node_folio_list, NODE_DATA(nid));
+		nr_reclaimed += reclaim_folio_list(&node_folio_list, nr_scanned,
+						   NODE_DATA(nid));
+		nr_scanned = 0;
 		nid = folio_nid(lru_to_folio(folio_list));
 	} while (!list_empty(folio_list));
 
-	nr_reclaimed += reclaim_folio_list(&node_folio_list, NODE_DATA(nid));
-
+	nr_reclaimed += reclaim_folio_list(&node_folio_list, nr_scanned,
+					   NODE_DATA(nid));
 	memalloc_noreclaim_restore(noreclaim_flag);
 
 	return nr_reclaimed;