From: Kairui Song <kasong@xxxxxxxxxxx>
When lru_gen is aging, it will update mm counters page by page,
which causes a higher overhead if age happens frequently or there
are a lot of pages in one generation getting moved.
Optimize this by doing the counter update in batch.
Although most __mod_*_state has its own caches the overhead
is still observable.
Tested in a 4G memcg on a EPYC 7K62 with:
memcached -u nobody -m 16384 -s /tmp/memcached.socket \
-a 0766 -t 16 -B binary &
memtier_benchmark -S /tmp/memcached.socket \
-P memcache_binary -n allkeys \
--key-minimum=1 --key-maximum=16000000 -d 1024 \
--ratio=1:0 --key-pattern=P:P -c 2 -t 16 --pipeline 8 -x 6
Average result of 18 test runs:
Before: 44017.78 Ops/sec
After: 44687.08 Ops/sec (+1.5%)
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
mm/vmscan.c | 64 +++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 55 insertions(+), 9 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b4ca3563bcf4..e3b4797b9729 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3095,9 +3095,47 @@ static int folio_update_gen(struct folio *folio, int gen)
return ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
}
+/*
+ * Update LRU gen in batch for each lru_gen LRU list. The batch is limited to
+ * each gen / type / zone level LRU. Batch is applied after finished or aborted
+ * scanning one LRU list.
+ */
+struct gen_update_batch {
+ int delta[MAX_NR_GENS];
+};
+
+static void lru_gen_update_batch(struct lruvec *lruvec, bool type, int zone,
+ struct gen_update_batch *batch)
+{
+ int gen;
+ int promoted = 0;
+ struct lru_gen_folio *lrugen = &lruvec->lrugen;
+ enum lru_list lru = type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
+
+ for (gen = 0; gen < MAX_NR_GENS; gen++) {
+ int delta = batch->delta[gen];
+
+ if (!delta)
+ continue;
+
+ WRITE_ONCE(lrugen->nr_pages[gen][type][zone],
+ lrugen->nr_pages[gen][type][zone] + delta);
+
+ if (lru_gen_is_active(lruvec, gen))
+ promoted += delta;
+ }
+
+ if (promoted) {
+ __update_lru_size(lruvec, lru, zone, -promoted);
+ __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, promoted);
+ }
+}
+
/* protect pages accessed multiple times through file descriptors */
-static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
+static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio,
+ bool reclaiming, struct gen_update_batch *batch)
{
+ int delta = folio_nr_pages(folio);
int type = folio_is_file_lru(folio);
struct lru_gen_folio *lrugen = &lruvec->lrugen;
int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
@@ -3120,7 +3158,8 @@ static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclai
new_flags |= BIT(PG_reclaim);
} while (!try_cmpxchg(&folio->flags, &old_flags, new_flags));
- lru_gen_update_size(lruvec, folio, old_gen, new_gen);
+ batch->delta[old_gen] -= delta;
+ batch->delta[new_gen] += delta;
return new_gen;
}
@@ -3663,6 +3702,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, bool can_swap)
{
int zone;
int remaining = MAX_LRU_BATCH;
+ struct gen_update_batch batch = { };
struct lru_gen_folio *lrugen = &lruvec->lrugen;
int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
@@ -3681,12 +3721,15 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, bool can_swap)
VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
- new_gen = folio_inc_gen(lruvec, folio, false);
+ new_gen = folio_inc_gen(lruvec, folio, false, &batch);
list_move_tail(&folio->lru, &lrugen->folios[new_gen][type][zone]);
- if (!--remaining)
+ if (!--remaining) {
+ lru_gen_update_batch(lruvec, type, zone, &batch);
return false;
+ }
}
+ lru_gen_update_batch(lruvec, type, zone, &batch);
}
done:
reset_ctrl_pos(lruvec, type, true);
@@ -4197,7 +4240,7 @@ static int lru_gen_memcg_seg(struct lruvec *lruvec)
******************************************************************************/
static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc,
- int tier_idx)
+ int tier_idx, struct gen_update_batch *batch)
{
bool success;
int gen = folio_lru_gen(folio);
@@ -4239,7 +4282,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
if (tier > tier_idx || refs == BIT(LRU_REFS_WIDTH)) {
int hist = lru_hist_from_seq(lrugen->min_seq[type]);
- gen = folio_inc_gen(lruvec, folio, false);
+ gen = folio_inc_gen(lruvec, folio, false, batch);
list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
WRITE_ONCE(lrugen->protected[hist][type][tier - 1],
@@ -4249,7 +4292,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
/* ineligible */
if (zone > sc->reclaim_idx || skip_cma(folio, sc)) {
- gen = folio_inc_gen(lruvec, folio, false);
+ gen = folio_inc_gen(lruvec, folio, false, batch);
list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
return true;
}
@@ -4257,7 +4300,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
/* waiting for writeback */
if (folio_test_locked(folio) || folio_test_writeback(folio) ||
(type == LRU_GEN_FILE && folio_test_dirty(folio))) {
- gen = folio_inc_gen(lruvec, folio, true);
+ gen = folio_inc_gen(lruvec, folio, true, batch);
list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
return true;
}
@@ -4323,6 +4366,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
for (i = MAX_NR_ZONES; i > 0; i--) {
LIST_HEAD(moved);
int skipped_zone = 0;
+ struct gen_update_batch batch = { };
int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES;
struct list_head *head = &lrugen->folios[gen][type][zone];
@@ -4337,7 +4381,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
scanned += delta;
- if (sort_folio(lruvec, folio, sc, tier))
+ if (sort_folio(lruvec, folio, sc, tier, &batch))
sorted += delta;
else if (isolate_folio(lruvec, folio, sc)) {
list_add(&folio->lru, list);
@@ -4357,6 +4401,8 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
skipped += skipped_zone;
}
+ lru_gen_update_batch(lruvec, type, zone, &batch);
+
if (!remaining || isolated >= MIN_LRU_BATCH)
break;
}
--
2.43.0
