On Sat, Oct 31, 2026 at 5:02 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 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.
>
> Signed-off-by: Ridong Chen <[email protected]>
> ---
> 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);
> + }
> + }
I feel this is wrong. Can we calculate the newest and
oldest generations from seq, then print them in order
from newest to oldest?
The nr_pages[] array isn't ordered from newest to
oldest or vice versa, as we have:
static inline int lru_gen_from_seq(unsigned long seq)
{
return seq % MAX_NR_GENS;
}
And I added a helper here:
https://lore.kernel.org/linux-mm/[email protected]/
+static inline unsigned long lruvec_gen_size(struct lru_gen_folio *lrugen,
+ int type, unsigned long seq)
+{
+ int gen = lru_gen_from_seq(seq);
+ unsigned long size = 0;
+
+ for (int zone = 0; zone < MAX_NR_ZONES; zone++)
+ size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
+ return size;
+}
Maybe you could port it here as a separate patch so it
can land earlier as part of your tracepoints series. We
could then use it in the next version of the swappiness
series.
Best,
Barry
