Hello Yu Zhao

Could you give me your comment? I am waiting for your opinion on the
reuse method. I'm planning to resend it as a complete patch with it.
Thank you.


On Tue, Sep 26, 2023 at 11:15 PM 김재원 [off-list ref] wrote:

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On Mon, Sep 25, 2023 at 10:20?PM Jaewon Kim [off-list ref] wrote:

quoted

As the legacy lru provides, the lru_gen needs some trace events for
debugging.

This commit introduces 2 trace events.
  trace_mm_vmscan_lru_gen_scan
  trace_mm_vmscan_lru_gen_evict

Each event is similar to the following legacy events.
  trace_mm_vmscan_lru_isolate,
  trace_mm_vmscan_lru_shrink_[in]active

We should just reuse trace_mm_vmscan_lru_isolate and
trace_mm_vmscan_lru_shrink_inactive instead of adding new tracepoints.

To reuse trace_mm_vmscan_lru_isolate, we'd just need to append two new
names to LRU_NAMES.

The naming of trace_mm_vmscan_lru_shrink_inactive might seem confusing
but it's how MGLRU maintains the compatibility, e.g., the existing
active/inactive counters in /proc/vmstat.

Hello

Actually I had tried to reuse them. But some value was not that compatible.
Let me try that way again.

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Hello Yu Zhao

Could you look into what I tried below? I reused the legacy trace events as you recommened.

For the nr_scanned for trace_mm_vmscan_lru_shrink_inactive, I just used the scanned returned from isolate_folios.
I thought this is right as scan_folios also uses its isolated.
 __count_vm_events(PGSCAN_ANON + type, isolated);
But I guess the scanned in scan_folios is actually the one used in shrink_inactive_list

please ignore nr_scanned thing above I just misread the code.

This is an example, I think it works well.

 mm_vmscan_lru_isolate: isolate_mode=0 classzone=2 order=0 nr_requested=4096 nr_scanned=64 nr_skipped=0 nr_taken=64 lru=inactive_file
 mm_vmscan_lru_shrink_inactive: nid=0 nr_scanned=64 nr_reclaimed=63 nr_dirty=0 nr_writeback=0 nr_congested=0 nr_immediate=0 nr_activate_anon=0 nr_activate_file=1 nr_ref_keep=0 nr_unmap_fail=0 priority=2 flags=RECLAIM_WB_FILE|RECLAIM_WB_ASYNC

quoted

I tested this on both 0 and 7 of /sys/kernel/mm/lru_gen/enabled

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a4e44f1c97c1..b61a0156559c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -4328,6 +4328,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
       int sorted = 0;
       int scanned = 0;
       int isolated = 0;
+       int skipped = 0;
       int remaining = MAX_LRU_BATCH;
       struct lru_gen_folio *lrugen = &lruvec->lrugen;
       struct mem_cgroup *memcg = lruvec_memcg(lruvec);

@@ -4341,7 +4342,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,

       for (i = MAX_NR_ZONES; i > 0; i--) {
               LIST_HEAD(moved);
-               int skipped = 0;
+               int skipped_zone = 0;
               int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES;
               struct list_head *head = &lrugen->folios[gen][type][zone];

@@ -4363,16 +4364,17 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
                               isolated += delta;
                       } else {
                               list_move(&folio->lru, &moved);
-                               skipped += delta;
+                               skipped_zone += delta;
                       }

-                       if (!--remaining || max(isolated, skipped) >= MIN_LRU_BATCH)
+                       if (!--remaining || max(isolated, skipped_zone) >= MIN_LRU_BATCH)
                               break;
               }

-               if (skipped) {
+               if (skipped_zone) {
                       list_splice(&moved, head);
-                       __count_zid_vm_events(PGSCAN_SKIP, zone, skipped);
+                       __count_zid_vm_events(PGSCAN_SKIP, zone, skipped_zone);
+                       skipped += skipped_zone;
               }

               if (!remaining || isolated >= MIN_LRU_BATCH)

@@ -4387,6 +4389,9 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
       __count_memcg_events(memcg, item, isolated);
       __count_memcg_events(memcg, PGREFILL, sorted);
       __count_vm_events(PGSCAN_ANON + type, isolated);
+       trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, MAX_LRU_BATCH,
+                                   scanned, skipped, isolated,
+                                   type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);

       /*
        * There might not be eligible folios due to reclaim_idx. Check the

@@ -4517,6 +4522,9 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap

retry:
       reclaimed = shrink_folio_list(&list, pgdat, sc, &stat, false);
       sc->nr_reclaimed += reclaimed;
+       trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
+                       scanned, reclaimed, &stat, sc->priority,
+                       type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);

       list_for_each_entry_safe_reverse(folio, next, &list, lru) {
               if (!folio_evictable(folio)) {