On Mon, Sep 7, 2026 at 12:25 PM Ridong Chen <[email protected]> wrote:
>
> From: Ridong Chen <[email protected]>
>
> 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, with
> the memcg id and the new max_seq alongside the anon and file min_seq.
> Paired with the mm_mglru_isolate_folios tracepoint it makes the full
> aging-to-eviction window observable per memcg.
>
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Ridong Chen <[email protected]>
> ---
> include/trace/events/vmscan.h | 30 ++++++++++++++++++++++++++++++
> mm/vmscan.c | 4 ++++
> 2 files changed, 34 insertions(+)
>
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index a0e3cf75294b..ab93c2f4b318 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -439,6 +439,36 @@ TRACE_EVENT(mm_mglru_isolate_folios,
> __entry->max_seq)
> );
>
> +TRACE_EVENT(mm_mglru_inc_max_seq,
> +
> + TP_PROTO(u64 memcg_id,
> + unsigned long max_seq,
> + unsigned long anon_min_seq,
> + unsigned long file_min_seq),
> +
> + TP_ARGS(memcg_id, max_seq, anon_min_seq, file_min_seq),
> +
> + TP_STRUCT__entry(
> + __field(u64, memcg_id)
> + __field(unsigned long, max_seq)
> + __field(unsigned long, anon_min_seq)
> + __field(unsigned long, file_min_seq)
> + ),
> +
> + TP_fast_assign(
> + __entry->memcg_id = memcg_id;
> + __entry->max_seq = max_seq;
> + __entry->anon_min_seq = anon_min_seq;
> + __entry->file_min_seq = file_min_seq;
> + ),
> +
> + TP_printk("memcg_id=%llu max_seq=%lu anon_min_seq=%lu
> file_min_seq=%lu",
> + __entry->memcg_id,
> + __entry->max_seq,
> + __entry->anon_min_seq,
> + __entry->file_min_seq)
> +);
> +
> TRACE_EVENT(mm_vmscan_write_folio,
>
> TP_PROTO(struct folio *folio),
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 771fe6827939..3c806a57d113 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4065,6 +4065,10 @@ 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(mem_cgroup_id(lruvec_memcg(lruvec)),
> + lrugen->max_seq,
> + lrugen->min_seq[LRU_GEN_ANON],
> + lrugen->min_seq[LRU_GEN_FILE]);
I suspect we also want to know the number of pages in each generation,
similar to:
/sys/kernel/debug # cat lru_gen
memcg 1 /
node 0
0 25672 0 85
1 25672 0 4249
2 25672 21 0
3 25672 0 0
memcg 19 /A
node 0
0 23036 0 0
1 23036 0 0
2 23036 0 0
3 23036 0 0
Best Regards
Barry
