[PATCH v4 9/9] mm/mglru: add tracepoint for inc_max_seq()
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From: Ridong Chen <ridong.chen@linux.dev>
Date: 2026-10-19 04:24:20
Also in:
bpf, cgroups, linux-mm, lkml
Subsystem:
memory management, memory management - mglru (multi-gen lru), memory management - reclaim, the rest · Maintainers:
Andrew Morton, Johannes Weiner, Linus Torvalds
From: Ridong Chen <redacted> Aging in MGLRU advances max_seq via inc_max_seq(), creating a new youngest generation. There is currently no tracepoint on this path, so the moment a new generation is created, and how the min_seq of each type trails behind it, cannot be observed as it happens. Add mm_mglru_inc_max_seq, emitted right after max_seq is bumped while the lruvec lock is still held, with the node id, memcg id, the new max_seq, the anon and file min_seq, and the number of pages in each generation for both types, summed over zones and clamped to >= 0 the same way the debugfs lru_gen file reports them. The nr_anon/nr_file arrays are indexed by generation slot, so the emitted max_seq/min_seq say which slot holds which seq. They are printed with __print_array(), so the output is hex and its length follows MAX_NR_GENS automatically. Only the lruvec is passed in; all of the above is collected in TP_fast_assign(), so inc_max_seq() does no extra work when the event is disabled. Paired with mm_mglru_scan_folios it makes the full aging-to-eviction window observable per memcg. Assisted-by: LLM Signed-off-by: Ridong Chen <redacted> --- mm/trace_vmscan.h | 47 +++++++++++++++++++++++++++++++++++++++++++++++ mm/vmscan.c | 2 ++ 2 files changed, 49 insertions(+)
diff --git a/mm/trace_vmscan.h b/mm/trace_vmscan.h
index 8148b8224422..cddf42b5849a 100644
--- a/mm/trace_vmscan.h
+++ b/mm/trace_vmscan.h@@ -456,6 +456,53 @@ TRACE_EVENT(mm_mglru_scan_folios, __entry->min_seq) ); +TRACE_EVENT(mm_mglru_inc_max_seq, + + TP_PROTO(struct lruvec *lruvec), + + TP_ARGS(lruvec), + + TP_STRUCT__entry( + __field(u64, memcg_id) + __field(unsigned long, max_seq) + __field(unsigned long, anon_min_seq) + __field(unsigned long, file_min_seq) + __array(unsigned long, nr_anon, MAX_NR_GENS) + __array(unsigned long, nr_file, MAX_NR_GENS) + __field(int, nid) + ), + + TP_fast_assign( + struct lru_gen_folio *lrugen = &lruvec->lrugen; + int gen, zone; + + __entry->memcg_id = mem_cgroup_id(lruvec_memcg(lruvec)); + __entry->max_seq = lrugen->max_seq; + __entry->anon_min_seq = lrugen->min_seq[LRU_GEN_ANON]; + __entry->file_min_seq = lrugen->min_seq[LRU_GEN_FILE]; + /* summed over zones and clamped to >= 0, as debugfs lru_gen does */ + for (gen = 0; gen < MAX_NR_GENS; gen++) { + __entry->nr_anon[gen] = 0; + __entry->nr_file[gen] = 0; + for (zone = 0; zone < MAX_NR_ZONES; zone++) { + __entry->nr_anon[gen] += + max(lrugen->nr_pages[gen][LRU_GEN_ANON][zone], 0L); + __entry->nr_file[gen] += + max(lrugen->nr_pages[gen][LRU_GEN_FILE][zone], 0L); + } + } + __entry->nid = lruvec_pgdat(lruvec)->node_id; + ), + + TP_printk("nid=%d memcg_id=%llu max_seq=%lu anon_min_seq=%lu file_min_seq=%lu nr_anon=%s nr_file=%s", + __entry->nid, + __entry->memcg_id, + __entry->max_seq, + __entry->anon_min_seq, + __entry->file_min_seq, + __print_array(__entry->nr_anon, MAX_NR_GENS, sizeof(unsigned long)), + __print_array(__entry->nr_file, MAX_NR_GENS, sizeof(unsigned long))) +); #endif /* CONFIG_LRU_GEN */ TRACE_EVENT(mm_vmscan_write_folio,
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d459678c5ee5..7b9b1aca5c88 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c@@ -4129,6 +4129,8 @@ static bool inc_max_seq(struct lruvec *lruvec, unsigned long seq, int swappiness WRITE_ONCE(lrugen->timestamps[next], jiffies); /* make sure preceding modifications appear */ smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1); + + trace_mm_mglru_inc_max_seq(lruvec); unlock: lruvec_unlock_irq(lruvec);
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2.34.1