[PATCH v6 5/7] mm/mglru: add tracepoint for scan_folios()

From: Ridong Chen <ridong.chen@linux.dev>
Date: 2026-11-03 02:57:34
Also in: bpf, cgroups, linux-mm, lkml
Reply to: Ridong Chen, 2026-11-03

From: Ridong Chen <redacted>

MGLRU's scan_folios() emits the classic-LRU tracepoint
trace_mm_vmscan_lru_isolate(), which predates MGLRU. It reports the
scan/isolate counts and the LRU type, but carries no generation or
memcg context, so a trace of an MGLRU run cannot tell which memcg a
given scan belongs to, nor how far reclaim has progressed through the
generations.

Add mm_mglru_scan_folios next to it, reporting the same counters plus
nr_sorted (folios moved to a younger generation by sort_folio()) and
the context the classic tracepoint lacks: the node id and memcg id of
the lruvec, and the max_seq, tier and min_seq of the type being
scanned.

Now that struct scan_control is visible to the trace header, pass sc,
lruvec, type and tier straight in and derive everything else in
TP_fast_assign(), so nothing is computed at the call site when the
event is disabled. The int fields are grouped at the end of the entry
to avoid padding on 64-bit.

scan_folios() is the MGLRU-specific layer where folios are actually
scanned, so it has no classic-LRU counterpart. The existing tracepoint
is left unchanged.

Tested-by: Barry Song <baohua@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Baoquan He <baoquan.he@linux.dev>
Signed-off-by: Ridong Chen <redacted>
---
 mm/trace_vmscan.h | 66 +++++++++++++++++++++++++++++++++++++++++++++++
 mm/vmscan.c       |  2 ++
 2 files changed, 68 insertions(+)

diff --git a/mm/trace_vmscan.h b/mm/trace_vmscan.h
index b2ad83e5f25e..8148b8224422 100644
--- a/mm/trace_vmscan.h
+++ b/mm/trace_vmscan.h

@@ -392,6 +392,72 @@ TRACE_EVENT(mm_vmscan_lru_isolate,
 		__print_symbolic(__entry->lru, LRU_NAMES))
 );
 
+#ifdef CONFIG_LRU_GEN
+TRACE_EVENT(mm_mglru_scan_folios,
+
+	TP_PROTO(struct lruvec *lruvec,
+		 struct scan_control *sc,
+		 unsigned long nr_requested,
+		 unsigned long nr_scanned,
+		 unsigned long nr_sorted,
+		 unsigned long nr_skipped,
+		 unsigned long nr_taken,
+		 int type,
+		 int tier),
+
+	TP_ARGS(lruvec, sc, nr_requested, nr_scanned, nr_sorted, nr_skipped,
+		nr_taken, type, tier),
+
+	TP_STRUCT__entry(
+		__field(u64, memcg_id)
+		__field(unsigned long, nr_requested)
+		__field(unsigned long, nr_scanned)
+		__field(unsigned long, nr_sorted)
+		__field(unsigned long, nr_skipped)
+		__field(unsigned long, nr_taken)
+		__field(unsigned long, max_seq)
+		__field(unsigned long, min_seq)
+		__field(int, nid)
+		__field(int, highest_zoneidx)
+		__field(int, order)
+		__field(int, lru)
+		__field(int, tier)
+	),
+
+	TP_fast_assign(
+		__entry->memcg_id = mem_cgroup_id(lruvec_memcg(lruvec));
+		__entry->nr_requested = nr_requested;
+		__entry->nr_scanned = nr_scanned;
+		__entry->nr_sorted = nr_sorted;
+		__entry->nr_skipped = nr_skipped;
+		__entry->nr_taken = nr_taken;
+		__entry->max_seq = lruvec->lrugen.max_seq;
+		__entry->min_seq = lruvec->lrugen.min_seq[type];
+		__entry->nid = lruvec_pgdat(lruvec)->node_id;
+		__entry->highest_zoneidx = sc->reclaim_idx;
+		__entry->order = sc->order;
+		__entry->lru = type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
+		__entry->tier = tier;
+	),
+
+	TP_printk("nid=%d memcg_id=%llu classzone=%d order=%d nr_requested=%lu nr_scanned=%lu nr_sorted=%lu nr_skipped=%lu nr_taken=%lu lru=%s max_seq=%lu tier=%d min_seq=%lu",
+		__entry->nid,
+		__entry->memcg_id,
+		__entry->highest_zoneidx,
+		__entry->order,
+		__entry->nr_requested,
+		__entry->nr_scanned,
+		__entry->nr_sorted,
+		__entry->nr_skipped,
+		__entry->nr_taken,
+		__print_symbolic(__entry->lru, LRU_NAMES),
+		__entry->max_seq,
+		__entry->tier,
+		__entry->min_seq)
+);
+
+#endif /* CONFIG_LRU_GEN */
+
 TRACE_EVENT(mm_vmscan_write_folio,
 
 	TP_PROTO(struct folio *folio),

diff --git a/mm/vmscan.c b/mm/vmscan.c
index f3ec19352e6d..3054175717ab 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -4833,6 +4833,8 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	trace_mm_vmscan_lru_isolate(sc, nr_to_scan,
 				    scanned, skipped, isolated,
 				    type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
+	trace_mm_mglru_scan_folios(lruvec, sc, nr_to_scan, scanned, sorted,
+				   skipped, isolated, type, tier);
 
 	*isolatedp = isolated;
 	return scanned;

-- 
2.34.1

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