Re: [PATCH 2/3] mm/mglru: add tracepoint for scan_folios()
From: Ridong Chen
Date: Sun Sep 13 2026 - 06:27:07 EST
On 9/11/2026 10:11 PM, Steven Rostedt wrote:
On Fri, 11 Sep 2026 15:28:47 +0800
Ridong Chen <ridong.chen@xxxxxxxxx> wrote:
diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 8a872990b4be..c39dfacef033 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -392,6 +392,69 @@ TRACE_EVENT(mm_vmscan_lru_isolate,
__print_symbolic(__entry->lru, LRU_NAMES))
);
+TRACE_EVENT(mm_mglru_scan_folios,
+
+ TP_PROTO(u64 memcg_id,
+ int highest_zoneidx,
+ int order,
+ unsigned long nr_requested,
+ unsigned long nr_scanned,
+ unsigned long nr_sorted,
+ unsigned long nr_skipped,
+ unsigned long nr_taken,
+ int lru,
+ unsigned long max_seq,
+ int tier,
+ unsigned long min_seq),
+
+ TP_ARGS(memcg_id, highest_zoneidx, order, nr_requested, nr_scanned,
+ nr_sorted, nr_skipped, nr_taken, lru, max_seq, tier, min_seq),
+
+ TP_STRUCT__entry(
+ __field(u64, memcg_id)
+ __field(int, highest_zoneidx)
+ __field(int, order)
+ __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(int, lru)
+ __field(unsigned long, max_seq)
+ __field(int, tier)
+ __field(unsigned long, min_seq)
Thank you very much for your review.
Please keep "int"s together. This creates a structure that is used to write
into the ring buffer. On 64bit machines, the above would add 4 bytes of
padding after each int, whereas:
__field(unsigned long, max_seq)
__field(unsigned long, min_seq)
__field(int, lru)
__field(int, tier)
would not.
Will upate.
+ ),
+
+ TP_fast_assign(
+ __entry->memcg_id = memcg_id;
+ __entry->highest_zoneidx = highest_zoneidx;
+ __entry->order = order;
+ __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->lru = lru;
+ __entry->max_seq = max_seq;
+ __entry->tier = tier;
+ __entry->min_seq = min_seq;
+ ),
+
+ TP_printk("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->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)
+);
+
TRACE_EVENT(mm_vmscan_write_folio,
TP_PROTO(struct folio *folio),
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2554a6513aa8..bd1b9ecf2e84 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4876,6 +4876,12 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
scanned, skipped, isolated,
type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
+ trace_mm_mglru_scan_folios(mem_cgroup_id(lruvec_memcg(lruvec)),
+ sc->reclaim_idx, sc->order, nr_to_scan,
+ scanned, sorted, skipped, isolated,
+ type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON,
+ lrugen->max_seq, tier,
+ lrugen->min_seq[type]);
Can't this information be processed in the tracepoint? That is:
TP_PROTO(struct lruvec *lruvec,
struct scan_control *sc,
struct lru_gen_folio *lrugen,
unsigned long nr_requested,
unsigned long nr_scanned,
unsigned long nr_sorted,
unsigned long nr_skipped,
unsigned long nr_taken,
int type),
TP_ARGS(lruvec, sc, lrugen, nr_requested, nr_scanned,
nr_sorted, nr_skipped, nr_taken, type),
TP_STRUCT__entry(
__field(u64, memcg_id)
__field(int, highest_zoneidx)
__field(int, order)
__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, lru)
__field(int, tier)
),
TP_fast_assign(
__entry->memcg_id = mem_cgroup_id(lruvec_memcg(lruvec));
__entry->highest_zoneidx = sc->reclaim_idx;
__entry->order = sc->order;
__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->lru = type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
__entry->max_seq = lrugen->max_seq;
__entry->tier = tier;
__entry->min_seq = lrugen->min_seq;
),
This moves the code to generate the parameters into the TP_fast_assign()
which is in a separate text section. It remove code from the work flow
improving instruction cache.
Same can be done for that trace_mm_vmscan_lru_isolate() trace event.
Sashiko has reported the same issue, so I updated my series [1] when I received Sashiko's report. Thank you again for pointing this out.
[1] https://lore.kernel.org/linux-mm/20260911102939.2485750-3-ridong.chen@xxxxxxxxx/
*isolatedp = isolated;
return scanned;
--
--
Best regards
Ridong