[PATCH v7 00/16] mm: mglru: fix swappiness behavior

[PATCH v7 00/16] mm: mglru: fix swappiness behavior

[Barry Song (Xiaomi)]

Classic LRU respects swappiness, while MGLRU only weakly
honors it when selecting the scan type. The fallback logic
can easily override the bias established by
get_type_to_scan(). As a result, swappiness has a much
smaller overall impact when changing from 1 to 200, as
shown by the data presented later in this cover letter.

In this patchset, patches 1-8 from Kairui introduce a model that uses
refaults to determine nr_to_scan[] for both file and anon in MGLRU.
For each reclaim operation, we calculate how many file and anon
folios to scan, similar to CLRU, rather than relying on
get_type_to_scan() and fallback mechanisms to decide what to
reclaim, which have proven rather unreliable in honoring swappiness.
This model also allows scanning and reclaiming from the two youngest
generations, including the youngest generation itself. This can help
resolve OOM situations[1] and reduce the need for aging.

As Kairui mentioned, the OOM reproducer was demonstrated
previously [2], and that series was merged in v7 [3].
The problem was largely alleviated as described, but not
completely fixed. Under higher memory pressure, the system
could still hit OOM. Before this series, Kairui could still
reproduce OOM after hundreds of iterations. With the fixing
patch in this series applied, the problem no longer occurs.

Patch 9 from Barry fixes a cold/hot inversion exacerbated by patches
1–8 (which also exists in mainline) and improves reclaim efficiency.

Patches 10-15 from Gaofei and Barry optimize aging based on folio
distribution imbalance and improve reclaim behavior at extreme
swappiness values such as 1 and 200.

Patch 16 from Bo Zhang addresses the GFP_NOIO issue in MGLRU.

After the patchset, the results track CLRU across the full swappiness
range (see table below), with more file scanning at low swappiness
and more anon scanning at high swappiness.

pgsteal_file
swappiness   CLRU          MGLRU         MGLRU+patches
1            6,620,680     745,968       6,249,276
36           807,807       508,974       569,354
71           553,144       417,700       419,718
106          402,880       402,474       329,145
141          240,293       337,797       296,131
176          187,682       330,045       260,850
200          0             343,949       128

pgsteal_anon
swappiness   CLRU          MGLRU         MGLRU+patches
1            4,436,199     2,671,934     4,960,289
36           2,858,117     3,032,747     3,066,513
71           3,042,392     2,827,735     3,258,388
106          3,292,622     3,184,314     3,217,699
141          3,612,869     2,999,000     3,417,135
176          3,827,154     3,134,127     3,720,778
200          13,825,283    3,269,753     14,551,425

pgscan_file
swappiness   CLRU          MGLRU         MGLRU+patches
1            11,853,625    877,311       13,703,243
36           1,016,826     582,783       680,534
71           662,823       474,772       467,822
106          496,374       451,285       356,494
141          277,109       382,604       307,866
176          206,261       372,059       268,584
200          0             393,608       128

pgscan_anon
swappiness   CLRU          MGLRU         MGLRU+patches
1            20,804,386    5,847,747     6,766,764
36           17,830,330    6,740,075     5,870,434
71           18,357,293    6,126,194     7,333,437
106          19,938,920    6,431,355     7,702,863
141          19,609,579    5,997,762     8,915,973
176          21,612,749    6,071,032     10,590,224
200          44,776,474    6,544,125     30,318,894

refault_file
swappiness   CLRU          MGLRU         MGLRU+patches
1            6,523,070     667,302       6,171,580
36           722,110       431,585       492,267
71           477,062       340,241       342,626
106          327,610       324,747       262,786
141          161,827       265,959       224,831
176          115,551       258,515       184,601
200          0             268,049       88

refault_anon
swappiness   CLRU          MGLRU         MGLRU+patches
1            867,728       552,829       1,382,052
36           419,635       657,745       675,629
71           536,299       611,345       706,445
106          580,742       693,689       718,644
141          706,151       639,850       785,236
176          706,499       685,086       906,427
200          4,693,850     733,273       5,489,076

With a normal swappiness setting (without extreme bias), I
see almost no noticeable performance difference between
the two versions.

For example, with `swappiness=60`, the average results
over 5 rounds are:
metric          W/o patch     W/ patch
real            1m49.273s     1m48.876s
user            25m33.186s    25m31.449s
sys             3m41.851s     3m39.935s

[1] https://github.com/ryncsn/emm-test-project/tree/master/file-anon-mix-pressure
[2] https://lore.kernel.org/all/20260318-mglru-reclaim-v1-0-2c46f9eb0508@tencent.com/
[3] https://lore.kernel.org/linux-mm/20260428-mglru-reclaim-v7-0-02fabb92dc43@tencent.com/

v7:
* fix a build error of bisect and address some other sashiko minor comments;
* add no-populatable aging;
v6 link:
  https://lore.kernel.org/linux-mm/20261110202025.25736-1-baohua@kernel.org/

v6:
* rebase on top of mm-new(a lot of conflicts due to recent active mglru
  developments);
* only count eligible zones below sc->reclaim_idx for
  lruvec_evictable_size() and lru_gen_imbalanced();
* GFP_NOIO further fixing by Bo Zhang, exclude unreclaimable type
  in lruvec_evictable_size().
* Add Kunwu's reviewed-by, thanks!
* RFC v5 link:
 https://lore.kernel.org/linux-mm/20261022220203.91911-1-baohua@kernel.org/

RFC v5:
* Remove the aging optimizations, which have been merged - thanks for Baolin,
  Baoqun, Lian Wang, Kairui, Kunwu, Ridong reviewing on this;
* Add Kairui's model for determining nr_to_scan[] for both types.
* Fix cold/hot inversion for rejected folios - Barry.
* Improve and clean up imbalanced aging, and optimize extreme
  swappiness values of 1 and 200 - Gaofei, Barry.
* Address the GFP_NOIO issue in MGLRU - Bo Zhang.
* RFC v4 link:
 https://lore.kernel.org/linux-mm/20260812121658.69965-1-baohua@kernel.org/

RFC v4:
* Clean up isolate_folios() based on Baolin's feedback. Thanks!
* Further improve isolate_folios() and scan_folios(), including
  handling of exhausted reclaim types.
* Add fixes and performance improvements to inc_min_seq(),
  and reduce lock contention.
* Improve the handling of imbalanced aging and remaining
  generation-based aging.
*  RFC v3 link:
 https://lore.kernel.org/linux-mm/20260731083843.37811-1-baohua@kernel.org/

RFC v3:
 - Added Ridong's patch of improving isolate_folios() readability;
 - for lru_gen_imbalanced(), apply some suggestions from Zicheng
   and Kairui, considering lruvec size and use macro;
 - drop "mm: mglru: only fall back when reclaim is running at high
   priority"
 - mitigate aging for balanced swappiess value(near middle 100)
   as swappiness bias is less a concern for them; but slightly
   increased aging overhead might not be good.
 *  RFC v2 link:
   https://lore.kernel.org/linux-mm/20260726122123.7614-1-baohua@kernel.org/

RFC v2:
 - Quickly address a few issues raised in the Sashiko comments so
   reviewers can ignore v1 and review a cleaner version instead.
   https://sashiko.dev/#/patchset/20260726012946.18684-1-baohua@kernel.org
   Thanks, Sashiko!

Barry Song (Xiaomi) (5):
  mm/mglru: Avoid placing rejected folios below populated gen
  mm/mglru: Run aging when one type has no populatable folios
  mm/mglru: Restrict eviction accounting to eligible zones
  mm/mglru: Reduce LRU lock contention by shrinking folio batches in
    inc_min_seq
  mm/mglru: Make swappiness=1 file reclaim more aggressive

Bo Zhang (1):
  mm/mglru: Avoid scan anon while swapcache is low for GFP_NOIO
    allocation

Kairui Song (8):
  mm/mglru: report evictable sizes per type
  mm/mglru: extract lruvec_populated_min_seq() helper
  mm/mglru: reclaim from the oldest populated gen
  mm/mglru: lift the forced protection of reclaimer
  mm/mglru: skip zones above reclaim_idx instead of rotating them
  mm/mglru: return for unavailable anon reclaim earlier
  mm/mglru: balance anon and file scan budget by refault rate
  mm/mglru: lift youngest gen protection for higher priority

lyugaofei (2):
  mm/mglru: Run aging when pages are rare outside the youngest gen
  mm/mglru: Avoid prolonged anon reclaim with swappiness=200

 include/linux/mm_inline.h |  22 +-
 mm/trace_vmscan.h         |   4 +-
 mm/vmscan.c               | 488 +++++++++++++++++++++++++-------------
 mm/vmscan.h               |   5 +-
 4 files changed, 343 insertions(+), 176 deletions(-)

-- 
2.34.1

[PATCH v7 01/16] mm/mglru: report evictable sizes per type

[Barry Song (Xiaomi)]

From: Kairui Song <kasong@tencent.com>

Change lruvec_evictable_size() to return the number of evictable
anonymous and file pages separately instead of a single total, so
that callers can weigh the two types independently.

Update lruvec_is_sizable() and get_nr_to_scan() accordingly; the
summed totals are unchanged, so there is no functional change.

Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 mm/vmscan.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 061fbd168d98..acc4efccda2f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4192,28 +4192,31 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
 	sc->priority = clamp(priority, DEF_PRIORITY / 2, DEF_PRIORITY);
 }
 
-static unsigned long lruvec_evictable_size(struct lruvec *lruvec, int swappiness)
+static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
+				  unsigned long nr[])
 {
 	int type;
-	unsigned long seq, total = 0;
+	unsigned long seq;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	DEFINE_MAX_SEQ(lruvec);
 	DEFINE_MIN_SEQ(lruvec);
 
+	nr[LRU_GEN_ANON] = 0;
+	nr[LRU_GEN_FILE] = 0;
+
 	for_each_evictable_type(type, swappiness) {
 		for (seq = min_seq[type]; seq <= max_seq; seq++)
-			total += lruvec_gen_size(lrugen, type, seq);
+			nr[type] += lruvec_gen_size(lrugen, type, seq);
 	}
-
-	return total;
 }
 
 static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
 {
-	unsigned long total;
+	unsigned long total, sizes[ANON_AND_FILE];
 	int swappiness = get_swappiness(lruvec, sc);
 
-	total = lruvec_evictable_size(lruvec, swappiness);
+	lruvec_evictable_size(lruvec, swappiness, sizes);
+	total = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
 
 	/* whether the size is big enough to be helpful */
 	return total >> sc->priority;
@@ -5021,7 +5024,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
 static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
 			   struct mem_cgroup *memcg, int swappiness)
 {
-	unsigned long nr_to_scan, evictable;
+	unsigned long nr_to_scan, evictable, sizes[ANON_AND_FILE];
 	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
 
 	/*
@@ -5037,7 +5040,8 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
 			return 0;
 	}
 
-	evictable = lruvec_evictable_size(lruvec, swappiness);
+	lruvec_evictable_size(lruvec, swappiness, sizes);
+	evictable = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
 
 	nr_to_scan = apply_proportional_protection(memcg, sc, evictable);
 	nr_to_scan >>= sc->priority;
-- 
2.34.1

[PATCH v7 02/16] mm/mglru: extract lruvec_populated_min_seq() helper

[Barry Song (Xiaomi)]

From: Kairui Song <kasong@tencent.com>

The search for the oldest populated generation of a type, previously
embedded in try_to_inc_min_seq(), is extracted into the new
lruvec_populated_min_seq() helper. It returns the oldest populated seq
of a given type, bounded by the given max_seq so the search never goes
beyond it.

No functional change.

Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 mm/vmscan.c | 43 +++++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index acc4efccda2f..4ac80968e634 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3991,30 +3991,45 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 	return true;
 }
 
+/* Similar to lruvec_evictable_size, return the oldest populated seq of the type */
+static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
+					      unsigned long max_seq)
+{
+	int gen, zone;
+	unsigned long min_seq;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+
+	lockdep_assert_held(&lruvec->lru_lock);
+
+	min_seq = READ_ONCE(lrugen->min_seq[type]);
+	while (min_seq <= max_seq) {
+		gen = lru_gen_from_seq(min_seq);
+		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
+			if (!list_empty(&lrugen->folios[gen][type][zone]))
+				return min_seq;
+		}
+		min_seq++;
+	}
+
+	return max_seq;
+}
+
 static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
 {
-	int gen, type, zone;
+	int type;
 	bool seq_inc_flag = false;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	DEFINE_MIN_SEQ(lruvec);
+	unsigned long seq;
 
 	VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
 
-	/* find the oldest populated generation */
+	/* Requires at least MIN_NR_GENS gens for basic functionality */
+	seq = lrugen->max_seq - MIN_NR_GENS;
 	for_each_evictable_type(type, swappiness) {
-		while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) {
-			gen = lru_gen_from_seq(min_seq[type]);
-
-			for (zone = 0; zone < MAX_NR_ZONES; zone++) {
-				if (!list_empty(&lrugen->folios[gen][type][zone]))
-					goto next;
-			}
-
-			min_seq[type]++;
+		min_seq[type] = lruvec_populated_min_seq(lruvec, type, seq + 1);
+		if (min_seq[type] > lrugen->min_seq[type])
 			seq_inc_flag = true;
-		}
-next:
-		;
 	}
 
 	/*
-- 
2.34.1

[PATCH v7 03/16] mm/mglru: reclaim from the oldest populated gen

[Barry Song (Xiaomi)]

From: Kairui Song <kasong@tencent.com>

Currently MGLRU tries to keep the gen numbers of the two types in sync,
avoiding reducing the gen number of one type when the other type has
more gens, as described in the comment in try_to_inc_min_seq().

This makes scan_folios() stuck reclaiming the type with fewer gens: it
always scanned the oldest gen of the type, even when that gen was
empty, so reclaim made no progress on that type unless forced aging
created a new gen and eliminated the dead empty gen.

There are other approaches, like lifting the gen number
synchronization [1]. However, that would break the gen layout used by
lru_gen_folio_seq(): newly added folios would no longer have a
well-defined hotness according to their gen number, which reduces
accuracy. It is also not pressure-aware, since with gentle reclaim we
still want to respect the gen layout (hotness).

Instead, reclaim from whichever populated oldest gen is left, but only
when the default reclaim priority can't satisfy the reclaimer's
requirement. This is typical for swappiness limitations: e.g., low
swappiness asks the reclaimer to reclaim from file, but file gens are
drained, so the reclaim cycle fails and priority is raised.

At the default priority the scan quota is 1/4096 of the evictable
size, and the old behavior is kept there to respect the hotness
distribution. Once priority is raised, the quota is at least 1/2048,
so the hotness bias introduced by reclaiming from a younger gen is
bounded by that quota, which seems fair. Global reclaim for MGLRU may
start with DEF_PRIORITY / 2 (1/64); the ratio is still reasonable at
that point, and when global pressure is more critical, we should
reclaim harder.

Note that scan_folios() still refuses to reclaim a type left with only
MIN_NR_GENS gens, so a completely drained type still requires aging.
This change only avoids scanning empty gens when populated reclaimable
gens remain.

Link: https://lore.kernel.org/linux-mm/20260726122123.7614-4-baohua@kernel.org/ [1]
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
Signed-off-by: Barry Song <baohua@kernel.org>
---
 mm/vmscan.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4ac80968e634..593f407c0668 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3311,11 +3311,9 @@ static int __folio_inc_gen(struct folio *folio, int old_gen, bool *increased)
 }
 
 /* protect pages accessed multiple times through file descriptors */
-static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio)
+static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, int old_gen)
 {
-	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]);
+	int new_gen;
 	bool gen_increased;
 
 	new_gen = __folio_inc_gen(folio, old_gen, &gen_increased);
@@ -4674,7 +4672,7 @@ void lru_gen_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent,
  ******************************************************************************/
 
 static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc,
-		       int tier_idx)
+		       int min_gen, int tier_idx)
 {
 	int gen = folio_lru_gen(folio);
 	int type = folio_is_file_lru(folio);
@@ -4692,14 +4690,14 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 		return false;
 
 	/* promoted */
-	if (gen != lru_gen_from_seq(lrugen->min_seq[type])) {
+	if (gen != min_gen) {
 		list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
 		return true;
 	}
 
 	/* protected */
 	if (tier > tier_idx || refs + workingset == BIT(LRU_REFS_WIDTH) + 1) {
-		gen = folio_inc_gen(lruvec, folio);
+		gen = folio_inc_gen(lruvec, folio, min_gen);
 		list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
 
 		/* don't count the workingset being lazily promoted */
@@ -4714,7 +4712,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 
 	/* ineligible */
 	if (zone > sc->reclaim_idx) {
-		gen = folio_inc_gen(lruvec, folio);
+		gen = folio_inc_gen(lruvec, folio, min_gen);
 		list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
 		return true;
 	}
@@ -4757,17 +4755,27 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	int scanned = 0;
 	int isolated = 0;
 	int skipped = 0;
+	unsigned long min_seq;
 	unsigned long remaining = nr_to_scan;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH);
 	VM_WARN_ON_ONCE(!list_empty(list));
 
+	/*
+	 * Respect the gen hotness distribution at low priority to avoid
+	 * aging and scan cost, but prefer to satisfy the reclaimers request
+	 * when under pressure to respect swappiness more and reduce IO cost.
+	 */
+	if (sc->priority == DEF_PRIORITY)
+		min_seq = lrugen->min_seq[type];
+	else
+		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq - MIN_NR_GENS + 1);
+
 	if (get_nr_gens(lruvec, type) == MIN_NR_GENS)
 		return 0;
 
-	gen = lru_gen_from_seq(lrugen->min_seq[type]);
-
+	gen = lru_gen_from_seq(min_seq);
 	for (i = MAX_NR_ZONES; i > 0; i--) {
 		LIST_HEAD(moved);
 		int skipped_zone = 0;
@@ -4785,7 +4793,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 
 			scanned += delta;
 
-			if (sort_folio(lruvec, folio, sc, tier))
+			if (sort_folio(lruvec, folio, sc, gen, tier))
 				sorted += delta;
 			else if (isolate_folio(lruvec, folio, sc)) {
 				list_add(&folio->lru, list);
-- 
2.34.1

[PATCH v7 04/16] mm/mglru: lift the forced protection of reclaimer

[Barry Song (Xiaomi)]

From: Kairui Song <kasong@tencent.com>

When a type is drained down to MIN_NR_GENS gens, the reclaimer will
fail to make any progress on that type without aging.

However aging comes with a cost, and it will take time to finish. Even
if we do aging more proactively, when under great pressure, gens will
still be drained very fast so the new gens produced by aging can't catch
up with the consumption. With MIN_NR_GENS setting blocking the reclaim,
we will run into OOM. This OOM can be reproduced by the previous test
program [1] used for fixing another aging problem [2]. When running in
great pressure, certain workloads will keep seeing premature OOM with
MGLRU, and never see any OOM with classical LRU.

This might get worse if we implement async aging, or avoid hotness
inversion in aging, as they will slow down the aging process even more.

To fix this, let's first drop the get_nr_gens() == MIN_NR_GENS early
return and let the raised-priority scan bound cover max_seq itself.

Mapped folios will still survive as the rmap PTE check will keep them.
Unmapped cache folios may thrashing more when under great pressure,
which is really a problem that should be fixed with refault distance
and frequecy aware promotoin instead [3].

Link: https://github.com/ryncsn/emm-test-project/tree/master/file-anon-mix-pressure [1]
Link: https://lore.kernel.org/linux-mm/20260428-mglru-reclaim-v7-0-02fabb92dc43@tencent.com/ [2]
Link: https://lore.kernel.org/linux-mm/20260502-mglru-fg-v1-0-913619b014d9@tencent.com/ [3]
Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 mm/vmscan.c | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 593f407c0668..db0a8a3e8887 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4672,7 +4672,7 @@ void lru_gen_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent,
  ******************************************************************************/
 
 static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc,
-		       int min_gen, int tier_idx)
+		       int min_gen, int max_gen, int tier_idx)
 {
 	int gen = folio_lru_gen(folio);
 	int type = folio_is_file_lru(folio);
@@ -4689,12 +4689,22 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	if (!folio_evictable(folio))
 		return false;
 
-	/* promoted */
+	/* promoted, or moved due to reparenting. */
 	if (gen != min_gen) {
 		list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
 		return true;
 	}
 
+	/*
+	 * We are reclaiming the last gen left. Folios in this gen can no
+	 * longer be promoted or protected, so just isolate them. The one
+	 * exception is lru_gen_reparent_memcg(), which is handled above.
+	 */
+	if (min_gen == max_gen) {
+		VM_WARN_ON_ONCE(zone > sc->reclaim_idx);
+		return false;
+	}
+
 	/* protected */
 	if (tier > tier_idx || refs + workingset == BIT(LRU_REFS_WIDTH) + 1) {
 		gen = folio_inc_gen(lruvec, folio, min_gen);
@@ -4749,15 +4759,16 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		       struct list_head *list, int *isolatedp)
 {
 	int i;
-	int gen;
 	enum node_stat_item item;
 	int sorted = 0;
 	int scanned = 0;
 	int isolated = 0;
 	int skipped = 0;
+	int gen, max_gen;
 	unsigned long min_seq;
 	unsigned long remaining = nr_to_scan;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+	DEFINE_MAX_SEQ(lruvec);
 
 	VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH);
 	VM_WARN_ON_ONCE(!list_empty(list));
@@ -4770,18 +4781,24 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	if (sc->priority == DEF_PRIORITY)
 		min_seq = lrugen->min_seq[type];
 	else
-		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq - MIN_NR_GENS + 1);
-
-	if (get_nr_gens(lruvec, type) == MIN_NR_GENS)
-		return 0;
+		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq);
 
 	gen = lru_gen_from_seq(min_seq);
+	max_gen = lru_gen_from_seq(max_seq);
+
 	for (i = MAX_NR_ZONES; i > 0; i--) {
 		LIST_HEAD(moved);
 		int skipped_zone = 0;
 		int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES;
 		struct list_head *head = &lrugen->folios[gen][type][zone];
 
+		/*
+		 * If there is only one gen left, rotating the unreclaimable
+		 * zone become meaningless, just skip them.
+		 */
+		if (gen == max_gen && zone > sc->reclaim_idx)
+			continue;
+
 		while (!list_empty(head)) {
 			struct folio *folio = lru_to_folio(head);
 			int delta = folio_nr_pages(folio);
@@ -4792,8 +4809,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 			VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
 
 			scanned += delta;
-
-			if (sort_folio(lruvec, folio, sc, gen, tier))
+			if (sort_folio(lruvec, folio, sc, gen, max_gen, tier))
 				sorted += delta;
 			else if (isolate_folio(lruvec, folio, sc)) {
 				list_add(&folio->lru, list);
-- 
2.34.1

[PATCH v7 05/16] mm/mglru: skip zones above reclaim_idx instead of rotating them

[Barry Song (Xiaomi)]

From: Kairui Song <kasong@tencent.com>

scan_folios() used to visit every zone. Folios in zones above
sc->reclaim_idx can never be isolated, so sort_folio() rotated them to
a younger generation, the "ineligible" branch, or, when only one gen
was left, skipped them. This wasted scan work on every pass, and the
rotation kept the protected folios from aging.

Restrict both the scan and the gen selection to the eligible zones,
like the legacy LRU, which only isolates folios in zones up to
reclaim_idx:

- lruvec_populated_min_seq() takes a zone_limit, so the oldest
  populated gen is searched only among the zones the scan can
  reclaim from. A gen populated only in protected zones no longer
  stalls the scan.
- scan_folios() iterates the eligible zones in the descending order
  of the legacy zonelist walk, draining the zone at reclaim_idx
  first.
- The ineligible branch of sort_folio() is now dead and removed,
  with a VM_WARN_ON_ONCE_FOLIO() guarding the new invariant.

try_to_inc_min_seq() still considers all zones, so min_seq[type] is
only bumped once the oldest gen is empty everywhere. At DEF_PRIORITY
the search bound stays min_seq[type], so the scan still starts from
the oldest gen regardless of whether it is populated.

Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 47 +++++++++++++++++++----------------------------
 1 file changed, 19 insertions(+), 28 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index db0a8a3e8887..6b1670677974 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3991,7 +3991,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 
 /* Similar to lruvec_evictable_size, return the oldest populated seq of the type */
 static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
-					      unsigned long max_seq)
+					      int zone_limit, unsigned long max_seq)
 {
 	int gen, zone;
 	unsigned long min_seq;
@@ -4002,7 +4002,7 @@ static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
 	min_seq = READ_ONCE(lrugen->min_seq[type]);
 	while (min_seq <= max_seq) {
 		gen = lru_gen_from_seq(min_seq);
-		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
+		for (zone = 0; zone < zone_limit; zone++) {
 			if (!list_empty(&lrugen->folios[gen][type][zone]))
 				return min_seq;
 		}
@@ -4025,7 +4025,7 @@ static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
 	/* Requires at least MIN_NR_GENS gens for basic functionality */
 	seq = lrugen->max_seq - MIN_NR_GENS;
 	for_each_evictable_type(type, swappiness) {
-		min_seq[type] = lruvec_populated_min_seq(lruvec, type, seq + 1);
+		min_seq[type] = lruvec_populated_min_seq(lruvec, type, MAX_NR_ZONES, seq + 1);
 		if (min_seq[type] > lrugen->min_seq[type])
 			seq_inc_flag = true;
 	}
@@ -4684,6 +4684,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	VM_WARN_ON_ONCE_FOLIO(gen >= MAX_NR_GENS, folio);
+	VM_WARN_ON_ONCE_FOLIO(zone > sc->reclaim_idx, folio);
 
 	/* unevictable: let it through and the generic path will cull it */
 	if (!folio_evictable(folio))
@@ -4700,10 +4701,8 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	 * longer be promoted or protected, so just isolate them. The one
 	 * exception is lru_gen_reparent_memcg(), which is handled above.
 	 */
-	if (min_gen == max_gen) {
-		VM_WARN_ON_ONCE(zone > sc->reclaim_idx);
+	if (min_gen == max_gen)
 		return false;
-	}
 
 	/* protected */
 	if (tier > tier_idx || refs + workingset == BIT(LRU_REFS_WIDTH) + 1) {
@@ -4720,13 +4719,6 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 		return true;
 	}
 
-	/* ineligible */
-	if (zone > sc->reclaim_idx) {
-		gen = folio_inc_gen(lruvec, folio, min_gen);
-		list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
-		return true;
-	}
-
 	return false;
 }
 
@@ -4758,16 +4750,17 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		       struct scan_control *sc, int type, int tier,
 		       struct list_head *list, int *isolatedp)
 {
-	int i;
 	enum node_stat_item item;
+	int zone_idx;
 	int sorted = 0;
 	int scanned = 0;
 	int isolated = 0;
 	int skipped = 0;
 	int gen, max_gen;
-	unsigned long min_seq;
+	unsigned long seq;
 	unsigned long remaining = nr_to_scan;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
 	DEFINE_MAX_SEQ(lruvec);
 
 	VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH);
@@ -4779,24 +4772,22 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	 * when under pressure to respect swappiness more and reduce IO cost.
 	 */
 	if (sc->priority == DEF_PRIORITY)
-		min_seq = lrugen->min_seq[type];
+		seq = lrugen->min_seq[type];
 	else
-		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq);
+		seq = lrugen->max_seq;
 
-	gen = lru_gen_from_seq(min_seq);
+	seq = lruvec_populated_min_seq(lruvec, type, sc->reclaim_idx + 1, seq);
+	gen = lru_gen_from_seq(seq);
 	max_gen = lru_gen_from_seq(max_seq);
 
-	for (i = MAX_NR_ZONES; i > 0; i--) {
+	/* Scan eligible zones in descending order. */
+	for (zone_idx = sc->reclaim_idx; zone_idx >= 0; zone_idx--) {
 		LIST_HEAD(moved);
 		int skipped_zone = 0;
-		int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES;
-		struct list_head *head = &lrugen->folios[gen][type][zone];
+		struct zone *zone = &pgdat->node_zones[zone_idx];
+		struct list_head *head = &lrugen->folios[gen][type][zone_idx];
 
-		/*
-		 * If there is only one gen left, rotating the unreclaimable
-		 * zone become meaningless, just skip them.
-		 */
-		if (gen == max_gen && zone > sc->reclaim_idx)
+		if (!managed_zone(zone))
 			continue;
 
 		while (!list_empty(head)) {
@@ -4806,7 +4797,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 			VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
 			VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
 			VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
-			VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
+			VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone_idx, folio);
 
 			scanned += delta;
 			if (sort_folio(lruvec, folio, sc, gen, max_gen, tier))
@@ -4825,7 +4816,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 
 		if (skipped_zone) {
 			list_splice(&moved, head);
-			__count_zid_vm_events(PGSCAN_SKIP, zone, skipped_zone);
+			__count_zid_vm_events(PGSCAN_SKIP, zone_idx, skipped_zone);
 			skipped += skipped_zone;
 		}
 
-- 
2.34.1

[PATCH v7 06/16] mm/mglru: return for unavailable anon reclaim earlier

[Barry Song (Xiaomi)]

From: Kairui Song <kasong@tencent.com>

No feature change, just shuffle some code, prepare for later commits.

Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 mm/vmscan.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6b1670677974..e2807faf26de 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5055,20 +5055,6 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
 			   struct mem_cgroup *memcg, int swappiness)
 {
 	unsigned long nr_to_scan, evictable, sizes[ANON_AND_FILE];
-	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
-
-	/*
-	 * Proactive reclaim initiated by userspace for anonymous memory only.
-	 * SWAPPINESS_ANON_ONLY is set only on the proactive reclaim path, so
-	 * warn if it shows up elsewhere. When anon cannot be reclaimed (e.g.
-	 * no swap), return 0 to skip the scan entirely, avoiding useless scan
-	 * work when there is nothing eligible to reclaim.
-	 */
-	if (swappiness == SWAPPINESS_ANON_ONLY) {
-		WARN_ON_ONCE(!sc->proactive);
-		if (!can_reclaim_anon_pages(memcg, pgdat->node_id, sc))
-			return 0;
-	}
 
 	lruvec_evictable_size(lruvec, swappiness, sizes);
 	evictable = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
@@ -5121,6 +5107,19 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 	int swappiness = get_swappiness(lruvec, sc);
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 
+	/*
+	 * Proactive reclaim initiated by userspace for anonymous memory only.
+	 * SWAPPINESS_ANON_ONLY is set only on the proactive reclaim path, so
+	 * warn if it shows up elsewhere. When anon cannot be reclaimed (e.g.
+	 * no swap), return 0 to skip the scan entirely, avoiding useless scan
+	 * work when there is nothing eligible to reclaim.
+	 */
+	if (swappiness == SWAPPINESS_ANON_ONLY) {
+		WARN_ON_ONCE(!sc->proactive);
+		if (!can_reclaim_anon_pages(memcg, lruvec_pgdat(lruvec)->node_id, sc))
+			return false;
+	}
+
 	nr_to_scan = get_nr_to_scan(lruvec, sc, memcg, swappiness);
 	while (nr_to_scan > 0) {
 		int delta;
-- 
2.34.1

[PATCH v7 07/16] mm/mglru: balance anon and file scan budget by refault rate

[Barry Song (Xiaomi)]

From: Kairui Song <kasong@tencent.com>

Replace get_type_to_scan() and isolate_folios(), which selected one
type per batch, with a proportional split of the scan budget between
anon and file, and scan both types each round.

lru_gen_balance_scan() splits the total by

        anon : file = swappiness * r_file * w_anon :
                      (MAX_SWAPPINESS - swappiness) * r_anon * w_file

where r_anon and r_file are the per-type refault rates scaled by
4096, clamped to [1, 4096]; a rate at the 4096 ceiling means the type
refaults at least as often as it is evicted. The w factors bias the
split toward the LRU sizes at mild swappiness and follow the IO cost
ratio at the extremes. Both rate accumulators start at MIN_LRU_BATCH,
so a type without eviction history reads as 100% until evictions
accumulate, and the floor of 1 keeps a type that never refaults from
zeroing out the other type's share. Swappiness 0 and
SWAPPINESS_ANON_ONLY keep their single-type behavior; at swappiness ==
MAX_SWAPPINESS the file factor is zero, so anon gets the whole budget,
as in the classical LRU; swappiness 1 no longer forces file-only
scanning as the old code did.

The proportional protection and priority reduction are applied to the
total once, before the split, and each budget is capped at its type's
evictable size. Regular reclaim derives the total from the evictable
sizes, so the budgets sum to it. The proactive path re-splits the
remaining target each round, so eviction keeps working while either
type makes progress, until the target is met or no progress is
possible. The debugfs scan_control gets .priority = DEF_PRIORITY so
eviction starts from the oldest gen and reports the default priority
in the tracepoints.

Signed-off-by: Kairui Song <kasong@tencent.com>
Co-developed-by: lyugaofei <lyugaofei@xiaomi.com>
Signed-off-by: lyugaofei <lyugaofei@xiaomi.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 218 +++++++++++++++++++++++++++++++++-------------------
 1 file changed, 137 insertions(+), 81 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index e2807faf26de..88567002b7ef 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4858,79 +4858,110 @@ static int get_tier_idx(struct lruvec *lruvec, int type)
 	return tier - 1;
 }
 
-static int get_type_to_scan(struct lruvec *lruvec, int swappiness)
+/*
+ * Balance the anon vs file scan budget using MGLRU's per-type refault
+ * rates, where swappiness is the relative IO cost of anon vs file (see
+ * Documentation/admin-guide/sysctl/vm.rst).
+ *
+ * On entry, nr[] holds the evictable size of each type, on return it
+ * holds each type's scan budget, bounded by its evictable size.
+ *
+ * LRU lock not needed: a stale snapshot merely skews the split for one pass,
+ * and MGLRU aging averages the fault rate so we can simply read it, no need
+ * to do any extra work here. If reclaim is blocked by unfair type hotness or
+ * stall aging, the priority will raise and a raised priority drives the
+ * aging.
+ *
+ * Calculation is basically based on following formula with a LRU size bias:
+ *
+ * anon : file = swappiness * r_file * w_anon :
+ *               (MAX_SWAPPINESS - swappiness) * r_anon * w_file
+ *
+ * r_file / r_anon: refault rate for file / anon.
+ * w_file / w_anon: LRU size weight of file / anon.
+ *
+ * We don't calculate the scan cost, MGLRU uses lazy promotion, which will
+ * cancel the scan budget natually.
+ */
+static void lru_gen_balance_scan(struct lruvec *lruvec, int swappiness,
+		unsigned long total_scan, unsigned long nr[])
 {
-	struct ctrl_pos sp, pv;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+	u64 refault_rate[ANON_AND_FILE], anon_factor, file_factor;
+	u64 anon_scan, file_scan, total;
+	u64 anon_weight, file_weight;
+	int size_bias;
 
-	if (swappiness <= MIN_SWAPPINESS + 1)
-		return LRU_GEN_FILE;
+	total = nr[LRU_GEN_ANON] + nr[LRU_GEN_FILE];
+	if (!total)
+		return;
 
-	if (swappiness >= MAX_SWAPPINESS)
-		return LRU_GEN_ANON;
-	/*
-	 * Compare the sum of all tiers of anon with that of file to determine
-	 * which type to scan.
-	 */
-	read_ctrl_pos(lruvec, LRU_GEN_ANON, LRU_TIER_MIN, LRU_TIER_MAX,
-		      swappiness, &sp);
-	read_ctrl_pos(lruvec, LRU_GEN_FILE, LRU_TIER_MIN, LRU_TIER_MAX,
-		      MAX_SWAPPINESS - swappiness, &pv);
+	if (swappiness <= MIN_SWAPPINESS) {
+		nr[LRU_GEN_ANON] = 0;
+		nr[LRU_GEN_FILE] = min_t(u64, total_scan, nr[LRU_GEN_FILE]);
+		return;
+	}
 
-	return positive_ctrl_err(&sp, &pv);
-}
+	if (swappiness == SWAPPINESS_ANON_ONLY) {
+		nr[LRU_GEN_FILE] = 0;
+		nr[LRU_GEN_ANON] = min_t(u64, total_scan, nr[LRU_GEN_ANON]);
+		return;
+	}
 
-static inline bool is_single_type_reclaim(int swappiness)
-{
-	return swappiness == MIN_SWAPPINESS ||
-	       swappiness == SWAPPINESS_ANON_ONLY;
-}
+	for (int type = LRU_GEN_ANON; type <= LRU_GEN_FILE; type++) {
+		int hist = lru_hist_from_seq(READ_ONCE(lrugen->min_seq[type]));
+		/* start at MIN_LRU_BATCH to smooth the rate on gen start */
+		u64 refaulted = MIN_LRU_BATCH, evicted = MIN_LRU_BATCH;
 
-static int isolate_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
-			  struct scan_control *sc, int swappiness,
-			  struct list_head *list, int *isolated,
-			  int *isolate_type, int *isolate_scanned)
-{
-	bool type_fallback_allowed = !is_single_type_reclaim(swappiness);
-	int type = get_type_to_scan(lruvec, swappiness);
-	int total_scanned = 0, scanned, tier;
-	bool tried = false;
+		for (int tier = 0; tier < MAX_NR_TIERS; tier++) {
+			refaulted += READ_ONCE(lrugen->avg_refaulted[type][tier]);
+			refaulted += atomic_long_read(&lrugen->refaulted[hist][type][tier]);
 
-retry:
-	tier = get_tier_idx(lruvec, type);
-	scanned = scan_folios(nr_to_scan, lruvec, sc,
-			      type, tier, list, isolated);
+			evicted += READ_ONCE(lrugen->avg_total[type][tier]);
+			evicted += atomic_long_read(&lrugen->evicted[hist][type][tier]);
+		}
 
-	total_scanned += scanned;
-	if (*isolated) {
-		*isolate_type = type;
-		*isolate_scanned = scanned;
-		return total_scanned;
+		/*
+		 * The rate scaled by 4096 to survive integer division, clamped
+		 * to [1, 4096] (~0% - 100%), the floor of 1 keeps a type that
+		 * never refaults from zeroing out the other type's share.
+		 */
+		refault_rate[type] = mul_u64_u64_div_u64(refaulted, 4096, evicted);
+		refault_rate[type] = clamp_t(u64, refault_rate[type], 1, 4096);
 	}
 
 	/*
-	 * We are running out of the current reclaim type. Fall back to
-	 * the other type if allowed.
+	 * The more extreme the swappiness, the wider the IO cost gap between
+	 * anon and file, so the split should follow the IO cost ratio rather
+	 * than the sizes. With a mild swappiness, balance the scan by the
+	 * actual LRU size more.
 	 */
-	if (!scanned && !tried && type_fallback_allowed) {
-		type = !type;
-		tried = true;
-		type_fallback_allowed = false;
-		goto retry;
-	}
+	size_bias = max(1, min(swappiness, MAX_SWAPPINESS - swappiness));
+	anon_weight = nr[LRU_GEN_ANON] + nr[LRU_GEN_FILE] / size_bias;
+	file_weight = nr[LRU_GEN_FILE] + nr[LRU_GEN_ANON] / size_bias;
+
+	anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
+	file_factor = (u64)(MAX_SWAPPINESS - swappiness) * refault_rate[LRU_GEN_ANON] * file_weight;
+
+	/* Cross-multiply the ratio above. */
+	anon_scan = mul_u64_u64_div_u64(total_scan, anon_factor, anon_factor + file_factor);
+	file_scan = (u64)total_scan - anon_scan;
+
 	/*
-	 * We scanned some folios but failed to isolate any due to promotions,
-	 * protections, or races. Retry once to avoid a larger loop.
+	 * Bound each type by its evictable size. Hand the exceeding part to
+	 * the other type. Any excess left when total_scan exceeds both sizes
+	 * is dropped, since it only stresses the scanner with no gain.
 	 */
-	if (scanned && !tried) {
-		tried = true;
-		goto retry;
-	}
-
-	return total_scanned;
+	if (anon_scan > nr[LRU_GEN_ANON])
+		file_scan += anon_scan - nr[LRU_GEN_ANON];
+	else if (file_scan > nr[LRU_GEN_FILE])
+		anon_scan += file_scan - nr[LRU_GEN_FILE];
+	nr[LRU_GEN_ANON] = min_t(u64, anon_scan, nr[LRU_GEN_ANON]);
+	nr[LRU_GEN_FILE] = min_t(u64, file_scan, nr[LRU_GEN_FILE]);
 }
 
 static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
-			struct scan_control *sc, int swappiness)
+			struct scan_control *sc, int type, int swappiness)
 {
 	LIST_HEAD(list);
 	LIST_HEAD(clean);
@@ -4939,8 +4970,8 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	enum node_stat_item item;
 	struct reclaim_stat stat;
 	struct lru_gen_mm_walk *walk;
-	int scanned, reclaimed;
-	int isolated = 0, nr_isolated = 0, type, type_scanned;
+	int tier, scanned, reclaimed;
+	int isolated = 0, nr_isolated = 0;
 	unsigned long total_reclaimed = 0;
 	bool skip_retry = false;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
@@ -4951,8 +4982,9 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	/* In case folio deletion left empty old gens, flush them */
 	try_to_inc_min_seq(lruvec, swappiness);
 
-	scanned = isolate_folios(nr_to_scan, lruvec, sc, swappiness,
-				 &list, &isolated, &type, &type_scanned);
+	tier = get_tier_idx(lruvec, type);
+	scanned = scan_folios(nr_to_scan, lruvec, sc,
+			      type, tier, &list, &isolated);
 	nr_isolated = isolated;
 	if (nr_isolated)
 		__mod_node_page_state(pgdat, NR_ISOLATED_ANON + type,
@@ -4974,7 +5006,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	if (isolated)
 		handle_reclaim_writeback(isolated, pgdat, sc, &stat);
 	trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
-			type_scanned, reclaimed, &stat, sc,
+			scanned, reclaimed, &stat, sc,
 			type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
 
 	list_for_each_entry_safe_reverse(folio, next, &list, lru) {
@@ -5051,18 +5083,18 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
 	return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq;
 }
 
-static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
-			   struct mem_cgroup *memcg, int swappiness)
+static void lru_gen_prepare_scan(struct lruvec *lruvec, struct scan_control *sc,
+		struct mem_cgroup *memcg, int swappiness,
+		unsigned long nr_to_scan[])
 {
-	unsigned long nr_to_scan, evictable, sizes[ANON_AND_FILE];
-
-	lruvec_evictable_size(lruvec, swappiness, sizes);
-	evictable = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
+	unsigned long total;
 
-	nr_to_scan = apply_proportional_protection(memcg, sc, evictable);
-	nr_to_scan >>= sc->priority;
+	lruvec_evictable_size(lruvec, swappiness, nr_to_scan);
+	total = nr_to_scan[LRU_GEN_ANON] + nr_to_scan[LRU_GEN_FILE];
 
-	return nr_to_scan;
+	total = apply_proportional_protection(memcg, sc, total);
+	total >>= sc->priority;
+	lru_gen_balance_scan(lruvec, swappiness, total, nr_to_scan);
 }
 
 static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
@@ -5095,6 +5127,30 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
 	return true;
 }
 
+static long evict_folio_lists(unsigned long nr_to_scan[], struct lruvec *lruvec,
+			     struct scan_control *sc, int swappiness, unsigned long max_batch)
+{
+	int type;
+	unsigned long batch, scanned, total_scanned = 0;
+
+	/*
+	 * Scan both types with the given budgets; the caller checks if
+	 * reclaim is satisfied after each pass.
+	 */
+	for (type = LRU_GEN_FILE; type >= LRU_GEN_ANON; type--) {
+		if (!nr_to_scan[type])
+			continue;
+
+		batch = min(nr_to_scan[type], max_batch);
+		scanned = evict_folios(batch, lruvec, sc, type, swappiness);
+
+		nr_to_scan[type] -= min(nr_to_scan[type], scanned);
+		total_scanned += scanned;
+	}
+
+	return total_scanned;
+}
+
 /*
  * For future optimizations:
  * 1. Defer try_to_inc_max_seq() to workqueues to reduce latency for memcg
@@ -5102,8 +5158,8 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
  */
 static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 {
+	unsigned long nr[ANON_AND_FILE];
 	bool need_rotate = false, should_age = false;
-	long nr_batch, nr_to_scan;
 	int swappiness = get_swappiness(lruvec, sc);
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 
@@ -5120,9 +5176,9 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 			return false;
 	}
 
-	nr_to_scan = get_nr_to_scan(lruvec, sc, memcg, swappiness);
-	while (nr_to_scan > 0) {
-		int delta;
+	lru_gen_prepare_scan(lruvec, sc, memcg, swappiness, nr);
+
+	while (nr[LRU_GEN_ANON] > 0 || nr[LRU_GEN_FILE] > 0) {
 		DEFINE_MAX_SEQ(lruvec);
 
 		if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg)) {
@@ -5137,9 +5193,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 			should_age = true;
 		}
 
-		nr_batch = min(nr_to_scan, MIN_LRU_BATCH);
-		delta = evict_folios(nr_batch, lruvec, sc, swappiness);
-		if (!delta)
+		if (!evict_folio_lists(nr, lruvec, sc, swappiness, MIN_LRU_BATCH))
 			break;
 
 		if (should_abort_scan(lruvec, sc))
@@ -5152,7 +5206,6 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 		if (root_reclaim(sc) && should_age)
 			break;
 
-		nr_to_scan -= delta;
 		cond_resched();
 	}
 
@@ -5764,8 +5817,8 @@ static int run_aging(struct lruvec *lruvec, unsigned long seq,
 static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_control *sc,
 			int swappiness, unsigned long nr_to_reclaim)
 {
-	int nr_batch;
 	DEFINE_MAX_SEQ(lruvec);
+	unsigned long nr_to_scan[ANON_AND_FILE];
 
 	if (seq + MIN_NR_GENS > max_seq)
 		return -EINVAL;
@@ -5781,8 +5834,11 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
 		if (sc->nr_reclaimed >= nr_to_reclaim)
 			return 0;
 
-		nr_batch = min(nr_to_reclaim - sc->nr_reclaimed, MAX_LRU_BATCH);
-		if (!evict_folios(nr_batch, lruvec, sc, swappiness))
+		lruvec_evictable_size(lruvec, swappiness, nr_to_scan);
+		lru_gen_balance_scan(lruvec, swappiness,
+				     nr_to_reclaim - sc->nr_reclaimed, nr_to_scan);
+
+		if (!evict_folio_lists(nr_to_scan, lruvec, sc, swappiness, MAX_LRU_BATCH))
 			return 0;
 
 		cond_resched();
-- 
2.34.1

[PATCH v7 08/16] mm/mglru: lift youngest gen protection for higher priority

[Barry Song (Xiaomi)]

From: Kairui Song <kasong@tencent.com>

The forced protection of younger generations contradicts the
goal of minimizing the I/O cost of reclaim. Under high memory
pressure, MGLRU can repeatedly trigger premature OOMs, while
the classic LRU does not.

The problem is that aging may fail to keep up with reclaim.
When this happens, reclaimers may all abort prematurely
because they see only empty generations or just two
generations remaining.

Proactive aging does not solve this problem either. The
number of threads performing proactive aging is limited,
while the number of concurrent reclaimers can be much
larger. This is a fundamental limitation of MGLRU. One
possible solution is to use an aging lock. However, the
aging lock introduces significant jitter under heavy memory
pressure and has been reported to cause noticeable lags
on Android.

Furthermore, the generation-based reclaim model can
conflict with the goal of swappiness, which is to minimize
I/O cost rather than blindly follow folio hotness.

The previous commit allowed reclaimers running at
non-default priorities to reclaim up to `lrugen->max_seq`,
while reclaimers at the default priority could reclaim only
up to `lrugen->min_seq`.

This patch further refines generation protection based on
reclaim priority. At the default priority, reclaimers can
reclaim generations down to `lrugen->min_seq - MIN_NR_GENS`.
As reclaim priority increases, reclaimers are progressively
allowed to reclaim younger generations.

With this graduated protection, premature OOMs are no
longer observed, while swappiness is also respected.

Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 mm/vmscan.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 88567002b7ef..fff7ee17eb0d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4767,12 +4767,14 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	VM_WARN_ON_ONCE(!list_empty(list));
 
 	/*
-	 * Respect the gen hotness distribution at low priority to avoid
-	 * aging and scan cost, but prefer to satisfy the reclaimers request
-	 * when under pressure to respect swappiness more and reduce IO cost.
+	 * Respect hotness at default priority, and only reach into the
+	 * newest generation when under severe pressure, so hot folios are
+	 * not evicted as soon as priority is raised.
 	 */
 	if (sc->priority == DEF_PRIORITY)
-		seq = lrugen->min_seq[type];
+		seq = lrugen->max_seq - MIN_NR_GENS;
+	else if (sc->priority > DEF_PRIORITY / 2)
+		seq = lrugen->max_seq - 1;
 	else
 		seq = lrugen->max_seq;
 
-- 
2.34.1

[PATCH v7 09/16] mm/mglru: Avoid placing rejected folios below populated gen

[Barry Song (Xiaomi)]

We used to scan only the oldest generation in scan_folios(). In
evict_folios(), we checked whether
lru_gen_folio_seq(lruvec, folio, false) == min_seq[type]. If so, the
folio was marked active and moved to younger generations.

This was itself buggy, as folios in generation min_seq[type] - 1
would not be marked active by folio_set_active(), potentially causing
a cold/hot inversion.

Besides this issue, the old approach also differs from the current
behavior, where we can scan fewer than two generations.
Now that we can scan younger generations, including the youngest
generation, this no longer prevents rejected folios from being placed
in a generation below or at the populated generation. Such rejected
folios would then be scanned again and again, resulting in extremely
low `pg_steal/pg_scan` ratios. For example:
  pgsteal_file: 2312605
  pgscan_file:  36465693
  reclamation efficiency: 6.34%

We pass `scanned_seq` to `move_folios_to_lru()` and make sure we either
promote the folio or place it in the youngest generation when the
populated generation is already the youngest one.
Also, folio_set_active() is no longer needed.

With this change, the results become:
  pgsteal_file: 2683815
  pgscan_file:  4224244
  reclamation efficiency: 63.53%

The sys time for building the kernel also decreased from 4m30.532s to
3m50.188s while swappiness==1.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 include/linux/mm_inline.h | 22 +++++++++++++++++++++-
 mm/vmscan.c               | 24 ++++++++++++------------
 2 files changed, 33 insertions(+), 13 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index da04d81a819c..0a055a3fe210 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -332,7 +332,8 @@ static inline unsigned long lru_gen_folio_seq(const struct lruvec *lruvec,
 	return max(READ_ONCE(lrugen->max_seq) - gen + 1, READ_ONCE(lrugen->min_seq[type]));
 }
 
-static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
+static inline bool __lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
+		unsigned long scanned_seq, bool reclaiming)
 {
 	unsigned long seq;
 	unsigned long flags;
@@ -347,6 +348,8 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
 		return false;
 
 	seq = lru_gen_folio_seq(lruvec, folio, reclaiming);
+	if (scanned_seq != -1UL)
+		seq = max(seq, min(scanned_seq + 1, lrugen->max_seq));
 	gen = lru_gen_from_seq(seq);
 	flags = (gen + 1UL) << LRU_GEN_PGOFF;
 	/* see the comment on MIN_NR_GENS about PG_active */
@@ -362,6 +365,17 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
 	return true;
 }
 
+static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
+{
+	return __lru_gen_add_folio(lruvec, folio, -1UL, reclaiming);
+}
+
+static inline bool lru_gen_add_rejected_folio(struct lruvec *lruvec, struct folio *folio,
+		unsigned long scanned_seq)
+{
+	return __lru_gen_add_folio(lruvec, folio, scanned_seq, false);
+}
+
 static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
 {
 	unsigned long flags;
@@ -420,6 +434,12 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
 	return false;
 }
 
+static inline bool lru_gen_add_rejected_folio(struct lruvec *lruvec, struct folio *folio,
+		unsigned long scanned_seq)
+{
+	return false;
+}
+
 static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
 {
 	return false;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index fff7ee17eb0d..c5c4d6418d46 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1864,7 +1864,8 @@ static bool too_many_isolated(struct pglist_data *pgdat, int file,
  *
  * Note: The caller must not hold any lruvec lock.
  */
-static unsigned int move_folios_to_lru(struct list_head *list, bool do_rotate)
+static unsigned int move_folios_to_lru(struct list_head *list, unsigned long seq,
+		bool do_rotate)
 {
 	int nr_pages, nr_moved = 0;
 	struct lruvec *lruvec = NULL;
@@ -1921,7 +1922,7 @@ static unsigned int move_folios_to_lru(struct list_head *list, bool do_rotate)
 		    !folio_test_referenced(folio) &&
 		    folio_ref_count(folio) == folio_expected_ref_count(folio))
 			lruvec_add_folio_tail(lruvec, folio);
-		else
+		else if (seq == -1UL || !lru_gen_add_rejected_folio(lruvec, folio, seq))
 			lruvec_add_folio(lruvec, folio);
 
 		nr_pages = folio_nr_pages(folio);
@@ -2040,7 +2041,7 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
 	nr_reclaimed = shrink_folio_list(&folio_list, pgdat, sc, &stat, false,
 					 lruvec_memcg(lruvec));
 
-	move_folios_to_lru(&folio_list, true);
+	move_folios_to_lru(&folio_list, -1UL, true);
 
 	mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(sc),
 					stat.nr_demoted);
@@ -2151,8 +2152,8 @@ static void shrink_active_list(unsigned long nr_to_scan,
 	/*
 	 * Move folios back to the lru list.
 	 */
-	nr_activate = move_folios_to_lru(&l_active, false);
-	nr_deactivate = move_folios_to_lru(&l_inactive, false);
+	nr_activate = move_folios_to_lru(&l_active, -1UL, false);
+	nr_deactivate = move_folios_to_lru(&l_inactive, -1UL, false);
 
 	count_vm_events(PGDEACTIVATE, nr_deactivate);
 	count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
@@ -4748,7 +4749,8 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
 
 static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		       struct scan_control *sc, int type, int tier,
-		       struct list_head *list, int *isolatedp)
+		       struct list_head *list, int *isolatedp,
+		       unsigned long *scanned_seq)
 {
 	enum node_stat_item item;
 	int zone_idx;
@@ -4779,6 +4781,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		seq = lrugen->max_seq;
 
 	seq = lruvec_populated_min_seq(lruvec, type, sc->reclaim_idx + 1, seq);
+	*scanned_seq = seq;
 	gen = lru_gen_from_seq(seq);
 	max_gen = lru_gen_from_seq(max_seq);
 
@@ -4975,6 +4978,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	int tier, scanned, reclaimed;
 	int isolated = 0, nr_isolated = 0;
 	unsigned long total_reclaimed = 0;
+	unsigned long scanned_seq;
 	bool skip_retry = false;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
@@ -4986,7 +4990,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 
 	tier = get_tier_idx(lruvec, type);
 	scanned = scan_folios(nr_to_scan, lruvec, sc,
-			      type, tier, &list, &isolated);
+			      type, tier, &list, &isolated, &scanned_seq);
 	nr_isolated = isolated;
 	if (nr_isolated)
 		__mod_node_page_state(pgdat, NR_ISOLATED_ANON + type,
@@ -5012,8 +5016,6 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 			type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
 
 	list_for_each_entry_safe_reverse(folio, next, &list, lru) {
-		DEFINE_MIN_SEQ(lruvec);
-
 		/* move_folios_to_lru() culls unevictable folios via folio_putback_lru() */
 		if (!folio_evictable(folio))
 			continue;
@@ -5032,11 +5034,9 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * so this effectively promotes them by at least one generation.
 		 */
 		folio_set_lru_refs(folio, 0);
-		if (lru_gen_folio_seq(lruvec, folio, false) == min_seq[type])
-			folio_set_active(folio);
 	}
 
-	move_folios_to_lru(&list, false);
+	move_folios_to_lru(&list, scanned_seq, false);
 
 	walk = current->reclaim_state->mm_walk;
 	if (walk && walk->batched) {
-- 
2.34.1

[PATCH v7 10/16] mm/mglru: Run aging when pages are rare outside the youngest gen

[Barry Song (Xiaomi)]

From: lyugaofei <lyugaofei@xiaomi.com>

Run aging when the total number of pages outside the youngest
generation across both types falls below 1/MAX_NR_GENS of the number
of pages in the youngest generation. For extreme swappiness values
such as 1 and 200, also consider the balance of the corresponding
type.

This improves reclaim efficiency, especially at extreme swappiness
values, while reducing system time.

To avoid the overhead of aging, we only allow imbalance-based aging
when the reclaim priority is low enough that we might reclaim the
youngest generation.

Signed-off-by: lyugaofei <lyugaofei@xiaomi.com>
Co-developed-by: Barry Song (Xiaomi) <baohua@kernel.org>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 41 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c5c4d6418d46..bf30c5b95478 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5068,6 +5068,41 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	return scanned;
 }
 
+static bool lru_gen_imbalanced(struct lruvec *lruvec, struct scan_control *sc,
+		int swappiness)
+{
+	unsigned long youngest[ANON_AND_FILE] = {0}, old[ANON_AND_FILE] = {0};
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+	DEFINE_MAX_SEQ(lruvec);
+	DEFINE_MIN_SEQ(lruvec);
+	int type;
+
+	if (sc->priority > DEF_PRIORITY / 2)
+		return false;
+
+	for_each_evictable_type(type, swappiness) {
+		unsigned long seq;
+
+		youngest[type] = lruvec_gen_size(lrugen, type, max_seq);
+		for (seq = min_seq[type]; seq < max_seq; seq++)
+			old[type] += lruvec_gen_size(lrugen, type, seq);
+	}
+
+	/* the vast majority of pages sit in the youngest gen */
+	if (youngest[LRU_GEN_ANON] + youngest[LRU_GEN_FILE] >
+	    (old[LRU_GEN_ANON] + old[LRU_GEN_FILE]) * MAX_NR_GENS)
+		return true;
+
+	/* Swappiness extremes: the corresponding type matters */
+	if (swappiness == MIN_SWAPPINESS + 1)
+		return youngest[LRU_GEN_FILE] > old[LRU_GEN_FILE] * MAX_NR_GENS;
+
+	if (swappiness == MAX_SWAPPINESS)
+		return youngest[LRU_GEN_ANON] > old[LRU_GEN_ANON] * MAX_NR_GENS;
+
+	return false;
+}
+
 static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
 			     struct scan_control *sc, int swappiness)
 {
@@ -5082,7 +5117,11 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
 		return false;
 
 	/* better to run aging even though eviction is still possible */
-	return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq;
+	if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq)
+		return true;
+
+	/* run aging when folios outside the youngest gen are rare */
+	return lru_gen_imbalanced(lruvec, sc, swappiness);
 }
 
 static void lru_gen_prepare_scan(struct lruvec *lruvec, struct scan_control *sc,
-- 
2.34.1

[PATCH v7 11/16] mm/mglru: Run aging when one type has no populatable folios

[Barry Song (Xiaomi)]

We may have scan budget remaining for anon or file
but no folios in populatable generations to scan.
In this case, `scan_folios()` may waste time scanning
that type while the other type still has populatable
folios.

Run aging in this case to make more folios
populatable. This also helps respect the scan budget
distribution determined by swappiness.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index bf30c5b95478..27c1547012bf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5104,7 +5104,8 @@ static bool lru_gen_imbalanced(struct lruvec *lruvec, struct scan_control *sc,
 }
 
 static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
-			     struct scan_control *sc, int swappiness)
+			     struct scan_control *sc, int swappiness,
+			     bool no_populatable)
 {
 	DEFINE_MIN_SEQ(lruvec);
 
@@ -5116,6 +5117,13 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
 	if (sc->priority == DEF_PRIORITY)
 		return false;
 
+	/*
+	 * Run aging if scan budget remains but no folios
+	 * in populatable generations are available to scan.
+	 */
+	if (no_populatable)
+		return true;
+
 	/* better to run aging even though eviction is still possible */
 	if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq)
 		return true;
@@ -5220,20 +5228,17 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 	lru_gen_prepare_scan(lruvec, sc, memcg, swappiness, nr);
 
 	while (nr[LRU_GEN_ANON] > 0 || nr[LRU_GEN_FILE] > 0) {
+		unsigned long orig_file, orig_anon;
 		DEFINE_MAX_SEQ(lruvec);
+		bool no_populatable;
 
 		if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg)) {
 			need_rotate = true;
 			break;
 		}
 
-		if (should_run_aging(lruvec, max_seq, sc, swappiness)) {
-			trace_mm_mglru_aging(lruvec, sc, swappiness);
-			if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false))
-				need_rotate = true;
-			should_age = true;
-		}
-
+		orig_anon = nr[LRU_GEN_ANON];
+		orig_file = nr[LRU_GEN_FILE];
 		if (!evict_folio_lists(nr, lruvec, sc, swappiness, MIN_LRU_BATCH))
 			break;
 
@@ -5247,6 +5252,15 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 		if (root_reclaim(sc) && should_age)
 			break;
 
+		no_populatable = (nr[LRU_GEN_ANON] && nr[LRU_GEN_ANON] == orig_anon) ||
+				 (nr[LRU_GEN_FILE] && nr[LRU_GEN_FILE] == orig_file);
+		if (should_run_aging(lruvec, max_seq, sc, swappiness, no_populatable)) {
+			trace_mm_mglru_aging(lruvec, sc, swappiness);
+			if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false))
+				need_rotate = true;
+			should_age = true;
+		}
+
 		cond_resched();
 	}
 
-- 
2.34.1

[PATCH v7 12/16] mm/mglru: Restrict eviction accounting to eligible zones

[Barry Song (Xiaomi)]

For both lruvec_evictable_size() and lru_gen_imbalanced(),
only count eligible zones below sc->reclaim_idx. This
avoids inflating the number of scanned pages and allows
aging to proceed more promptly when eligible zones have
few folios.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/trace_vmscan.h |  4 ++--
 mm/vmscan.c       | 18 +++++++++---------
 mm/vmscan.h       |  5 +++--
 3 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/mm/trace_vmscan.h b/mm/trace_vmscan.h
index 565c56428364..9dafdb5bd3ce 100644
--- a/mm/trace_vmscan.h
+++ b/mm/trace_vmscan.h
@@ -488,9 +488,9 @@ TRACE_EVENT(mm_mglru_aging,
 			unsigned long seq = max_seq - MAX_NR_GENS + 1 + i;
 
 			__entry->nr_anon[i] =
-				lruvec_gen_size(lrugen, LRU_GEN_ANON, seq);
+				lruvec_gen_size(lrugen, LRU_GEN_ANON, seq, MAX_NR_ZONES);
 			__entry->nr_file[i] =
-				lruvec_gen_size(lrugen, LRU_GEN_FILE, seq);
+				lruvec_gen_size(lrugen, LRU_GEN_FILE, seq, MAX_NR_ZONES);
 		}
 		__entry->nid = lruvec_pgdat(lruvec)->node_id;
 		__entry->priority = sc->priority;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 27c1547012bf..7a48b82ea4c1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4206,8 +4206,8 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
 	sc->priority = clamp(priority, DEF_PRIORITY / 2, DEF_PRIORITY);
 }
 
-static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
-				  unsigned long nr[])
+static void lruvec_evictable_size(struct lruvec *lruvec, struct scan_control *sc,
+				  int swappiness, unsigned long nr[])
 {
 	int type;
 	unsigned long seq;
@@ -4220,7 +4220,7 @@ static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
 
 	for_each_evictable_type(type, swappiness) {
 		for (seq = min_seq[type]; seq <= max_seq; seq++)
-			nr[type] += lruvec_gen_size(lrugen, type, seq);
+			nr[type] += lruvec_gen_size(lrugen, type, seq, sc->reclaim_idx + 1);
 	}
 }
 
@@ -4229,7 +4229,7 @@ static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
 	unsigned long total, sizes[ANON_AND_FILE];
 	int swappiness = get_swappiness(lruvec, sc);
 
-	lruvec_evictable_size(lruvec, swappiness, sizes);
+	lruvec_evictable_size(lruvec, sc, swappiness, sizes);
 	total = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
 
 	/* whether the size is big enough to be helpful */
@@ -5083,9 +5083,9 @@ static bool lru_gen_imbalanced(struct lruvec *lruvec, struct scan_control *sc,
 	for_each_evictable_type(type, swappiness) {
 		unsigned long seq;
 
-		youngest[type] = lruvec_gen_size(lrugen, type, max_seq);
+		youngest[type] = lruvec_gen_size(lrugen, type, max_seq, sc->reclaim_idx + 1);
 		for (seq = min_seq[type]; seq < max_seq; seq++)
-			old[type] += lruvec_gen_size(lrugen, type, seq);
+			old[type] += lruvec_gen_size(lrugen, type, seq, sc->reclaim_idx + 1);
 	}
 
 	/* the vast majority of pages sit in the youngest gen */
@@ -5138,7 +5138,7 @@ static void lru_gen_prepare_scan(struct lruvec *lruvec, struct scan_control *sc,
 {
 	unsigned long total;
 
-	lruvec_evictable_size(lruvec, swappiness, nr_to_scan);
+	lruvec_evictable_size(lruvec, sc, swappiness, nr_to_scan);
 	total = nr_to_scan[LRU_GEN_ANON] + nr_to_scan[LRU_GEN_FILE];
 
 	total = apply_proportional_protection(memcg, sc, total);
@@ -5836,7 +5836,7 @@ static int lru_gen_seq_show(struct seq_file *m, void *v)
 			char mark = full && seq < min_seq[type] ? 'x' : ' ';
 
 			seq_printf(m, " %10lu%c",
-				   lruvec_gen_size(lrugen, type, seq), mark);
+				   lruvec_gen_size(lrugen, type, seq, MAX_NR_ZONES), mark);
 		}
 
 		seq_putc(m, '\n');
@@ -5889,7 +5889,7 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
 		if (sc->nr_reclaimed >= nr_to_reclaim)
 			return 0;
 
-		lruvec_evictable_size(lruvec, swappiness, nr_to_scan);
+		lruvec_evictable_size(lruvec, sc, swappiness, nr_to_scan);
 		lru_gen_balance_scan(lruvec, swappiness,
 				     nr_to_reclaim - sc->nr_reclaimed, nr_to_scan);
 
diff --git a/mm/vmscan.h b/mm/vmscan.h
index c6b583fc7493..2599d7c614ac 100644
--- a/mm/vmscan.h
+++ b/mm/vmscan.h
@@ -119,12 +119,13 @@ struct scan_control {
 #ifdef CONFIG_LRU_GEN
 /* The number of pages of @type in the generation @seq, summed over all zones */
 static inline unsigned long lruvec_gen_size(struct lru_gen_folio *lrugen,
-					    int type, unsigned long seq)
+					    int type, unsigned long seq,
+					    int max_zone)
 {
 	int gen = lru_gen_from_seq(seq);
 	unsigned long size = 0;
 
-	for (int zone = 0; zone < MAX_NR_ZONES; zone++)
+	for (int zone = 0; zone < max_zone; zone++)
 		size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
 
 	return size;
-- 
2.34.1

[PATCH v7 13/16] mm/mglru: Reduce LRU lock contention by shrinking folio batches in inc_min_seq

[Barry Song (Xiaomi)]

Reduce the number of folios moved from the oldest generation to the
second-oldest generation in each batch. This shortens the time the
lruvec lock is held, allowing concurrent LRU operations to make
progress and significantly reducing LRU lock contention.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7a48b82ea4c1..6315edf50376 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3911,7 +3911,7 @@ static inline void flush_lru_batch(struct list_head *head, struct list_head **ba
 static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 {
 	int zone;
-	int remaining = MAX_LRU_BATCH;
+	int remaining = MIN_LRU_BATCH;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	int hist = lru_hist_from_seq(lrugen->min_seq[type]);
 	int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
-- 
2.34.1

[PATCH v7 14/16] mm/mglru: Avoid prolonged anon reclaim with swappiness=200

[Barry Song (Xiaomi)]

From: lyugaofei <lyugaofei@xiaomi.com>

It has been observed that swappiness=200 can significantly slow down
reclaim on some machines, with some workloads running 3x slower
under MGLRU than under CLRU.

This is because swappiness=200 currently results in file_factor=0.
Give file reclaim a small factor at lower priorities, for example,
when sc->priority < DEF_PRIORITY / 2.

Signed-off-by: lyugaofei <lyugaofei@xiaomi.com>
Co-developed-by: Barry Song (Xiaomi) <baohua@kernel.org>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6315edf50376..3872305bac2a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4888,8 +4888,8 @@ static int get_tier_idx(struct lruvec *lruvec, int type)
  * We don't calculate the scan cost, MGLRU uses lazy promotion, which will
  * cancel the scan budget natually.
  */
-static void lru_gen_balance_scan(struct lruvec *lruvec, int swappiness,
-		unsigned long total_scan, unsigned long nr[])
+static void lru_gen_balance_scan(struct lruvec *lruvec, struct scan_control *sc,
+		int swappiness, unsigned long total_scan, unsigned long nr[])
 {
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	u64 refault_rate[ANON_AND_FILE], anon_factor, file_factor;
@@ -4946,7 +4946,12 @@ static void lru_gen_balance_scan(struct lruvec *lruvec, int swappiness,
 	file_weight = nr[LRU_GEN_FILE] + nr[LRU_GEN_ANON] / size_bias;
 
 	anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
-	file_factor = (u64)(MAX_SWAPPINESS - swappiness) * refault_rate[LRU_GEN_ANON] * file_weight;
+	if (swappiness == MAX_SWAPPINESS)
+		file_factor = sc->priority < DEF_PRIORITY / 2 ?
+			      refault_rate[LRU_GEN_ANON] * file_weight : 0;
+	else
+		file_factor = (u64)(MAX_SWAPPINESS - swappiness) *
+			      refault_rate[LRU_GEN_ANON] * file_weight;
 
 	/* Cross-multiply the ratio above. */
 	anon_scan = mul_u64_u64_div_u64(total_scan, anon_factor, anon_factor + file_factor);
@@ -5143,7 +5148,7 @@ static void lru_gen_prepare_scan(struct lruvec *lruvec, struct scan_control *sc,
 
 	total = apply_proportional_protection(memcg, sc, total);
 	total >>= sc->priority;
-	lru_gen_balance_scan(lruvec, swappiness, total, nr_to_scan);
+	lru_gen_balance_scan(lruvec, sc, swappiness, total, nr_to_scan);
 }
 
 static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
@@ -5890,7 +5895,7 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
 			return 0;
 
 		lruvec_evictable_size(lruvec, sc, swappiness, nr_to_scan);
-		lru_gen_balance_scan(lruvec, swappiness,
+		lru_gen_balance_scan(lruvec, sc, swappiness,
 				     nr_to_reclaim - sc->nr_reclaimed, nr_to_scan);
 
 		if (!evict_folio_lists(nr_to_scan, lruvec, sc, swappiness, MAX_LRU_BATCH))
-- 
2.34.1

[PATCH v7 15/16] mm/mglru: Make swappiness=1 file reclaim more aggressive

[Barry Song (Xiaomi)]

In MGLRU, swappiness=200 favors anon reclaim, while swappiness=1
favors file reclaim. Swappiness=0 allows only file reclaim, while
swappiness=201 allows only anon reclaim. Thus, swappiness=1 and
swappiness=200 are counterparts for file and anon reclaim,
respectively.

Before this patchset, get_type_to_scan() always returned
LRU_GEN_ANON for swappiness=200 and LRU_GEN_FILE for swappiness=1.

For swappiness=200, file_factor is set to 0 at higher reclaim
priorities. Similarly, anon_factor is set to 0 for swappiness=1
at higher reclaim priorities, making the two settings behave
similarly, although the thresholds are slightly different.

This allows file pages to be reclaimed more aggressively and
benefits workloads that prioritize file reclaim by using
swappiness=1.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3872305bac2a..d51303a5cb67 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4945,7 +4945,11 @@ static void lru_gen_balance_scan(struct lruvec *lruvec, struct scan_control *sc,
 	anon_weight = nr[LRU_GEN_ANON] + nr[LRU_GEN_FILE] / size_bias;
 	file_weight = nr[LRU_GEN_FILE] + nr[LRU_GEN_ANON] / size_bias;
 
-	anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
+	if (swappiness == MIN_SWAPPINESS + 1)
+		anon_factor = sc->priority <= DEF_PRIORITY / 2 ?
+			      refault_rate[LRU_GEN_FILE] * anon_weight : 0;
+	else
+		anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
 	if (swappiness == MAX_SWAPPINESS)
 		file_factor = sc->priority < DEF_PRIORITY / 2 ?
 			      refault_rate[LRU_GEN_ANON] * file_weight : 0;
-- 
2.34.1

[PATCH v7 16/16] mm/mglru: Avoid scan anon while swapcache is low for GFP_NOIO allocation

[Barry Song (Xiaomi)]

From: Bo Zhang <zhangbo56@xiaomi.com>

With GFP_NOIO, we cannot reclaim anon folios unless they are in
the swap cache. CLRU skips anon reclaim when the swap cache is
very low by commit 74d9aa0d8e98 ("mm: vmscan: avoid anon scanning
for GFP_NOIO with low swapcache"). Apply the same logic to MGLRU.

The new scan-budget-based mechanism makes this straightforward to
implement. Thanks also to Xiang Liu, who previously attempted to fix
this before we had the scan-budget-based model [1].

[1] https://lore.kernel.org/linux-mm/179248830836.1744016.8424217811286616919.noio-mglru-rfc-v2@bytedance.com/

Cc: Xiang Liu <liuxiang.277@bytedance.com>
Signed-off-by: Bo Zhang <zhangbo56@xiaomi.com>
Co-developed-by: Barry Song (Xiaomi) <baohua@kernel.org>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Reviewed-by: Kunwu Chan <chentao@kylinos.cn>
---
 mm/vmscan.c | 27 ++++++++++-----------------
 1 file changed, 10 insertions(+), 17 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d51303a5cb67..9f759d213614 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -272,13 +272,6 @@ static inline bool reclaimable_anon_is_low(struct mem_cgroup *memcg,
 	if (!sc || (sc->gfp_mask & __GFP_IO))
 		return false;
 
-	/*
-	 * FIXME: MGLRU doesn't fully respect can_reclaim_anon_pages() for the
-	 * scanning type, so only apply this to the traditional LRU for now.
-	 */
-	if (lru_gen_enabled())
-		return false;
-
 	if (memcg) {
 		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
 
@@ -4212,6 +4205,8 @@ static void lruvec_evictable_size(struct lruvec *lruvec, struct scan_control *sc
 	int type;
 	unsigned long seq;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+	int nid = lruvec_pgdat(lruvec)->node_id;
 	DEFINE_MAX_SEQ(lruvec);
 	DEFINE_MIN_SEQ(lruvec);
 
@@ -4219,6 +4214,8 @@ static void lruvec_evictable_size(struct lruvec *lruvec, struct scan_control *sc
 	nr[LRU_GEN_FILE] = 0;
 
 	for_each_evictable_type(type, swappiness) {
+		if (type == LRU_GEN_ANON && !can_reclaim_anon_pages(memcg, nid, sc))
+			continue;
 		for (seq = min_seq[type]; seq <= max_seq; seq++)
 			nr[type] += lruvec_gen_size(lrugen, type, seq, sc->reclaim_idx + 1);
 	}
@@ -4893,23 +4890,19 @@ static void lru_gen_balance_scan(struct lruvec *lruvec, struct scan_control *sc,
 {
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	u64 refault_rate[ANON_AND_FILE], anon_factor, file_factor;
-	u64 anon_scan, file_scan, total;
+	u64 anon_scan, file_scan;
 	u64 anon_weight, file_weight;
 	int size_bias;
 
-	total = nr[LRU_GEN_ANON] + nr[LRU_GEN_FILE];
-	if (!total)
-		return;
-
-	if (swappiness <= MIN_SWAPPINESS) {
+	if (swappiness <= MIN_SWAPPINESS)
 		nr[LRU_GEN_ANON] = 0;
-		nr[LRU_GEN_FILE] = min_t(u64, total_scan, nr[LRU_GEN_FILE]);
-		return;
-	}
 
-	if (swappiness == SWAPPINESS_ANON_ONLY) {
+	if (swappiness == SWAPPINESS_ANON_ONLY)
 		nr[LRU_GEN_FILE] = 0;
+
+	if (!nr[LRU_GEN_ANON] || !nr[LRU_GEN_FILE]) {
 		nr[LRU_GEN_ANON] = min_t(u64, total_scan, nr[LRU_GEN_ANON]);
+		nr[LRU_GEN_FILE] = min_t(u64, total_scan, nr[LRU_GEN_FILE]);
 		return;
 	}
 
-- 
2.34.1

Re: [PATCH v7 02/16] mm/mglru: extract lruvec_populated_min_seq() helper

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm/mglru: shadowed local variable seq in try_to_inc_min_seq()
--

commit 7a4927e9f0aa8623b1c83f69afd1fb935c342dd5
Author: Kairui Song <kasong@tencent.com>

mm/mglru: extract lruvec_populated_min_seq() helper

This commit extracts the search for the oldest populated generation of a
type from try_to_inc_min_seq() into a new lruvec_populated_min_seq()
helper.

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ed224cb80a75a..f98cd483f014a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c

[ ... ]

>  static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
>  {
> -	int gen, type, zone;
> +	int type;
>  	bool seq_inc_flag = false;
>  	struct lru_gen_folio *lrugen = &lruvec->lrugen;
>  	DEFINE_MIN_SEQ(lruvec);
> +	unsigned long seq;
>  
>  	VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
>  
> -	/* find the oldest populated generation */
> +	/* Requires at least MIN_NR_GENS gens for basic functionality */
> +	seq = lrugen->max_seq - MIN_NR_GENS;
>  	for_each_evictable_type(type, swappiness) {
> -		while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) {
> -			gen = lru_gen_from_seq(min_seq[type]);
> -
> -			for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> -				if (!list_empty(&lrugen->folios[gen][type][zone]))
> -					goto next;
> -			}
> -
> -			min_seq[type]++;
> +		min_seq[type] = lruvec_populated_min_seq(lruvec, type, seq + 1);
> +		if (min_seq[type] > lrugen->min_seq[type])
>  			seq_inc_flag = true;
> -		}
> -next:
> -		;
>  	}

[Severity: Low]
This isn't a bug, but adding seq at function scope causes the existing
inner declaration in try_to_inc_min_seq() to shadow it and recompute the
same value:

mm/vmscan.c:try_to_inc_min_seq() {
	...
	if (swappiness && swappiness <= MAX_SWAPPINESS) {
		unsigned long seq = lrugen->max_seq - MIN_NR_GENS;
	...
}

Dropping the inner declaration would avoid the -Wshadow warning under W=2
and reuse the value already computed.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=2

Re: [PATCH v7 03/16] mm/mglru: reclaim from the oldest populated gen

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm/mglru: uninitialized sc.priority in lru_gen_seq_write() skews
  scan_folios()
--

commit c250a15f7ef946582fda6b278da38054c0ad3a66
Author: Kairui Song <kasong@tencent.com>

mm/mglru: reclaim from the oldest populated gen

This commit updates scan_folios() to scan from the oldest populated
generation when sc->priority is raised from DEF_PRIORITY, passing that
generation down to sort_folio() and folio_inc_gen().

Link: https://lore.kernel.org/linux-mm/20260726122123.7614-4-baohua@kernel.org/ [1]

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f98cd483f014a..20199232dd70c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c

[ ... ]

> @@ -4758,17 +4756,27 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	int scanned = 0;
>  	int isolated = 0;
>  	int skipped = 0;
> +	unsigned long min_seq;
>  	unsigned long remaining = nr_to_scan;
>  	struct lru_gen_folio *lrugen = &lruvec->lrugen;
>  
>  	VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH);
>  	VM_WARN_ON_ONCE(!list_empty(list));
>  
> +	/*
> +	 * Respect the gen hotness distribution at low priority to avoid
> +	 * aging and scan cost, but prefer to satisfy the reclaimers request
> +	 * when under pressure to respect swappiness more and reduce IO cost.
> +	 */
> +	if (sc->priority == DEF_PRIORITY)
> +		min_seq = lrugen->min_seq[type];
> +	else
> +		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq - MIN_NR_GENS + 1);

[Severity: Low]
Does debugfs eviction via lru_gen_seq_write() take the raised-priority
branch here because sc.priority is left zero-initialized?

lru_gen_seq_write() allocates struct scan_control sc on the stack without
setting .priority = DEF_PRIORITY, so sc.priority is 0.  When an eviction
command runs while one type's oldest generation is empty and the other
type keeps get_nr_gens() above MIN_NR_GENS, scan_folios() treats the
call as raised priority and advances min_seq up to max_seq - MIN_NR_GENS + 1,
evicting folios from generations younger than the requested min_gen_nr
(including active generations that run_eviction() rejects).

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=3

Re: [PATCH v7 04/16] mm/mglru: lift the forced protection of reclaimer

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm/mglru: run_eviction() evicts up to max_seq due to sc.priority
  == 0
--

commit cd86952996e1243807567af19d65b021c3573888
Author: Kairui Song <kasong@tencent.com>

mm/mglru: lift the forced protection of reclaimer

This commit drops the MIN_NR_GENS early return in scan_folios() and
extends the raised-priority scan bound up to max_seq so reclaim can
proceed when aging cannot keep up with pressure.

Link: https://github.com/ryncsn/emm-test-project/tree/master/file-anon-mix-pressure [1]
Link: https://lore.kernel.org/linux-mm/20260428-mglru-reclaim-v7-0-02fabb92dc43@tencent.com/ [2]
Link: https://lore.kernel.org/linux-mm/20260502-mglru-fg-v1-0-913619b014d9@tencent.com/ [3]

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 20199232dd70c..51c2ee66b3ee8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c

[ ... ]

> @@ -4771,18 +4782,24 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	if (sc->priority == DEF_PRIORITY)
>  		min_seq = lrugen->min_seq[type];
>  	else
> -		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq - MIN_NR_GENS + 1);
> -
> -	if (get_nr_gens(lruvec, type) == MIN_NR_GENS)
> -		return 0;
> +		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq);

[Severity: Low]
Can debugfs proactive eviction via lru_gen_seq_write() -> run_eviction()
now scan and evict folios up to lrugen->max_seq instead of stopping at
the requested target seq?

lru_gen_seq_write() leaves sc.priority zero-initialized (0 !=
DEF_PRIORITY), and run_eviction() loops while seq >=
evictable_min_seq(min_seq, swappiness).  When one evictable type has no
folios in generations <= seq while the other still has min_seq <= seq,
scan_folios() takes the sc->priority != DEF_PRIORITY branch and evicts
folios from newer generations up to max_seq, where sort_folio() also
bypasses tier and reference protection when min_gen == max_gen.

The commit message of later commit "mm/mglru: balance anon and file scan
budget by refault rate" in this series notes setting .priority =
DEF_PRIORITY for the debugfs scan_control, but that initialization is
missing from the code.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=4

Re: [PATCH v7 05/16] mm/mglru: skip zones above reclaim_idx instead of rotating them

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [High] mm/mglru: pinned min_seq in try_to_inc_min_seq() stalls aging
--

commit a9558af5b6eefdf9bb9a64058218b290ef8ecc66
Author: Kairui Song <kasong@tencent.com>

mm/mglru: skip zones above reclaim_idx instead of rotating them

This commit restricts scan_folios() and lruvec_populated_min_seq() to zones up
to sc->reclaim_idx instead of scanning and rotating folios in higher zones.

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 51c2ee66b3ee8..273aa8c56bec8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3992,7 +3992,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
>  
>  /* Similar to lruvec_evictable_size, return the oldest populated seq of the type */
>  static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
> -					      unsigned long max_seq)
> +					      int zone_limit, unsigned long max_seq)
>  {
>  	int gen, zone;
>  	unsigned long min_seq;
> @@ -4003,7 +4003,7 @@ static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
>  	min_seq = READ_ONCE(lrugen->min_seq[type]);
>  	while (min_seq <= max_seq) {
>  		gen = lru_gen_from_seq(min_seq);
> -		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> +		for (zone = 0; zone < zone_limit; zone++) {
>  			if (!list_empty(&lrugen->folios[gen][type][zone]))
>  				return min_seq;
>  		}
> @@ -4026,7 +4026,7 @@ static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
>  	/* Requires at least MIN_NR_GENS gens for basic functionality */
>  	seq = lrugen->max_seq - MIN_NR_GENS;
>  	for_each_evictable_type(type, swappiness) {
> -		min_seq[type] = lruvec_populated_min_seq(lruvec, type, seq + 1);
> +		min_seq[type] = lruvec_populated_min_seq(lruvec, type, MAX_NR_ZONES, seq + 1);
>  		if (min_seq[type] > lrugen->min_seq[type])
>  			seq_inc_flag = true;
>  	}

[ ... ]

> @@ -4780,24 +4773,22 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	 * when under pressure to respect swappiness more and reduce IO cost.
>  	 */
>  	if (sc->priority == DEF_PRIORITY)
> -		min_seq = lrugen->min_seq[type];
> +		seq = lrugen->min_seq[type];
>  	else
> -		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq);
> +		seq = lrugen->max_seq;
>  
> -	gen = lru_gen_from_seq(min_seq);
> +	seq = lruvec_populated_min_seq(lruvec, type, sc->reclaim_idx + 1, seq);
> +	gen = lru_gen_from_seq(seq);
>  	max_gen = lru_gen_from_seq(max_seq);
>  
> -	for (i = MAX_NR_ZONES; i > 0; i--) {
> +	/* Scan eligible zones in descending order. */
> +	for (zone_idx = sc->reclaim_idx; zone_idx >= 0; zone_idx--) {

[Severity: High]
As reported by KunWu Chan on RFC v5 [1], does skipping zones above
sc->reclaim_idx in scan_folios() while try_to_inc_min_seq() still checks all
MAX_NR_ZONES stall aging during zone-constrained reclaim (for example,
GFP_DMA32 reclaim when ZONE_NORMAL is populated)?

When an lruvec has MAX_NR_GENS (4) generations, lrugen->min_seq[type] starts
at max_seq - 3.  Because scan_folios() no longer rotates folios in zones above
sc->reclaim_idx, any folios in those zones keep try_to_inc_min_seq() from
advancing lrugen->min_seq[type] once eligible zones are drained.

In should_run_aging():

mm/vmscan.c:should_run_aging() {
	...
	if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq)
		return true;

	/* try to avoid aging, do gentle reclaim at the default priority */
	if (sc->priority == DEF_PRIORITY)
		return false;

	/* better to run aging even though eviction is still possible */
	return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq;
}

With min_seq pinned at max_seq - 3, evictable_min_seq() + MIN_NR_GENS never
reaches max_seq, so should_run_aging() returns false and scan_folios() drains
eligible zones down to the youngest generation max_seq where sort_folio()
disables tier protection and workingset promotion (min_gen == max_gen).

Even with the follow-up commits in this series (commit "mm/mglru: Run aging
when pages are rare outside the youngest gen", commit "mm/mglru: Run aging
when one type has no populatable folios", and commit "mm/mglru: Restrict
eviction accounting to eligible zones"), at priorities above DEF_PRIORITY / 2
scan_folios() caps seq at max_seq - 1 and evict_folio_lists() returns 0 once
older generations are empty in eligible zones, causing try_to_shrink_lruvec()
to break out before calling should_run_aging() until priority drops to
DEF_PRIORITY / 2 and scans max_seq without tier protection.

[1] https://lore.kernel.org/r/CAN_Opa-AScm9=EeXO_Uy8VjbQ=bqY9P++rFP8H1RhUB4dOt6xw@mail.gmail.com

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=5

Re: [PATCH v7 07/16] mm/mglru: balance anon and file scan budget by refault rate

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential
issues to consider:
- [High] mm/mglru: non-real-name handle in Co-developed-by and
  Signed-off-by trailers
- [Medium] mm/mglru: missing DEF_PRIORITY initialization in
  lru_gen_seq_write()
- [Medium] mm/mglru: lru_gen_balance_scan() budgets un-scannable young
  generations
--

commit 730defb97ea747f35c6996e786706ce8e9143280
Author: Kairui Song <kasong@tencent.com>

> mm/mglru: balance anon and file scan budget by refault rate
>
> Replace get_type_to_scan() and isolate_folios(), which selected one
> type per batch, with a proportional split of the scan budget between
> anon and file, and scan both types each round.
>
> lru_gen_balance_scan() splits the total by
>
>         anon : file = swappiness * r_file * w_anon :
>                       (MAX_SWAPPINESS - swappiness) * r_anon * w_file
>
> where r_anon and r_file are the per-type refault rates scaled by
> 4096, clamped to [1, 4096]; a rate at the 4096 ceiling means the type
> refaults at least as often as it is evicted. The w factors bias the
> split toward the LRU sizes at mild swappiness and follow the IO cost
> ratio at the extremes. Both rate accumulators start at MIN_LRU_BATCH,
> so a type without eviction history reads as 100% until evictions
> accumulate, and the floor of 1 keeps a type that never refaults from
> zeroing out the other type's share. Swappiness 0 and
> SWAPPINESS_ANON_ONLY keep their single-type behavior; at swappiness ==
> MAX_SWAPPINESS the file factor is zero, so anon gets the whole budget,
> as in the classical LRU; swappiness 1 no longer forces file-only
> scanning as the old code did.
>
> The proportional protection and priority reduction are applied to the
> total once, before the split, and each budget is capped at its type's
> evictable size. Regular reclaim derives the total from the evictable
> sizes, so the budgets sum to it. The proactive path re-splits the
> remaining target each round, so eviction keeps working while either
> type makes progress, until the target is met or no progress is
> possible. The debugfs scan_control gets .priority = DEF_PRIORITY so
> eviction starts from the oldest gen and reports the default priority
> in the tracepoints.
>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> Co-developed-by: lyugaofei <lyugaofei@xiaomi.com>
> Signed-off-by: lyugaofei <lyugaofei@xiaomi.com>
> Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>

[Severity: High]
Under Documentation/process/submitting-patches.rst, Co-developed-by: and
Signed-off-by: tags must use a real full name rather than an account
handle ("lyugaofei").

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2ddaf6181c5d4..d7b4e36cf7415 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
[ ... ]
> @@ -5052,18 +5084,18 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
>  	return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq;
>  }
>  
> -static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
> -			   struct mem_cgroup *memcg, int swappiness)
> +static void lru_gen_prepare_scan(struct lruvec *lruvec, struct scan_control *sc,
> +		struct mem_cgroup *memcg, int swappiness,
> +		unsigned long nr_to_scan[])
>  {
> -	unsigned long nr_to_scan, evictable, sizes[ANON_AND_FILE];
> -
> -	lruvec_evictable_size(lruvec, swappiness, sizes);
> -	evictable = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
> +	unsigned long total;
>  
> -	nr_to_scan = apply_proportional_protection(memcg, sc, evictable);
> -	nr_to_scan >>= sc->priority;
> +	lruvec_evictable_size(lruvec, swappiness, nr_to_scan);
> +	total = nr_to_scan[LRU_GEN_ANON] + nr_to_scan[LRU_GEN_FILE];
>  
> -	return nr_to_scan;
> +	total = apply_proportional_protection(memcg, sc, total);
> +	total >>= sc->priority;
> +	lru_gen_balance_scan(lruvec, swappiness, total, nr_to_scan);
>  }
[ ... ]
> +static long evict_folio_lists(unsigned long nr_to_scan[], struct lruvec *lruvec,
> +			     struct scan_control *sc, int swappiness, unsigned long max_batch)
> +{
> +	int type;
> +	unsigned long batch, scanned, total_scanned = 0;
> +
> +	/*
> +	 * Scan both types with the given budgets; the caller checks if
> +	 * reclaim is satisfied after each pass.
> +	 */
> +	for (type = LRU_GEN_FILE; type >= LRU_GEN_ANON; type--) {
> +		if (!nr_to_scan[type])
> +			continue;
> +
> +		batch = min(nr_to_scan[type], max_batch);
> +		scanned = evict_folios(batch, lruvec, sc, type, swappiness);
> +
> +		nr_to_scan[type] -= min(nr_to_scan[type], scanned);
> +		total_scanned += scanned;
> +	}
> +
> +	return total_scanned;
> +}

[Severity: Medium]
Can lru_gen_balance_scan() assign scan budget to a type whose scannable
generations are empty, losing that budget instead of handing it to the
other type?

Previously, isolate_folios() fell back to !type whenever scan_folios()
returned 0.  Now lru_gen_prepare_scan() caps each type's budget by
lruvec_evictable_size(), which sums all generations from min_seq[type]
through max_seq:

mm/vmscan.c:lruvec_evictable_size() {
    ...
	for_each_evictable_type(type, swappiness) {
		for (seq = min_seq[type]; seq <= max_seq; seq++)
			nr[type] += lruvec_gen_size(lrugen, type, seq);
	}
}

At sc->priority == DEF_PRIORITY (or sc->priority > DEF_PRIORITY / 2 after
commit "mm/mglru: lift youngest gen protection for higher priority"),
scan_folios() only scans older generations and cannot scan max_seq - 1 or
max_seq.  When one type has drained its scannable generations while still
holding folios in younger protected generations, lruvec_evictable_size()
reports a non-zero nr[type], so lru_gen_balance_scan() does not transfer
its share of total_scan to the other type.

When the other type receives a 0 share (such as at swappiness ==
MAX_SWAPPINESS when anon's scannable generations are empty, or when small
total_scan rounds down to 0), evict_folio_lists() returns 0 and aborts
try_to_shrink_lruvec() immediately even though the other type still has
cold evictable folios.  When both types receive non-zero budgets,
evict_folios() returns 0 on the drained type and leaves its nr_to_scan
entry unchanged, causing repeated no-op evict_folios() calls on every
MIN_LRU_BATCH pass before discarding that unspent budget.

[ ... ]
> @@ -5765,8 +5818,8 @@ static int run_aging(struct lruvec *lruvec, unsigned long seq,
>  static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_control *sc,
>  			int swappiness, unsigned long nr_to_reclaim)
>  {
> -	int nr_batch;
>  	DEFINE_MAX_SEQ(lruvec);
> +	unsigned long nr_to_scan[ANON_AND_FILE];
>  
>  	if (seq + MIN_NR_GENS > max_seq)
>  		return -EINVAL;
> @@ -5782,8 +5835,11 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
>  		if (sc->nr_reclaimed >= nr_to_reclaim)
>  			return 0;
>  
> -		nr_batch = min(nr_to_reclaim - sc->nr_reclaimed, MAX_LRU_BATCH);
> -		if (!evict_folios(nr_batch, lruvec, sc, swappiness))
> +		lruvec_evictable_size(lruvec, swappiness, nr_to_scan);
> +		lru_gen_balance_scan(lruvec, swappiness,
> +				     nr_to_reclaim - sc->nr_reclaimed, nr_to_scan);
> +
> +		if (!evict_folio_lists(nr_to_scan, lruvec, sc, swappiness, MAX_LRU_BATCH))
>  			return 0;

[Severity: Medium]
Was .priority = DEF_PRIORITY accidentally dropped from the scan_control in
lru_gen_seq_write()?

The commit message notes that the debugfs scan_control gets
.priority = DEF_PRIORITY so eviction starts from the oldest generation and
reports the default priority in tracepoints, but lru_gen_seq_write() leaves
sc.priority zero-initialized:

mm/vmscan.c:lru_gen_seq_write() {
    ...
	struct scan_control sc = {
		.may_writepage = true,
		.may_unmap = true,
		.may_swap = true,
		.reclaim_idx = MAX_NR_ZONES - 1,
		.gfp_mask = GFP_KERNEL,
		.proactive = true,
	};
    ...
}

With sc.priority == 0, run_eviction() -> evict_folio_lists() ->
evict_folios() -> scan_folios() takes the sc->priority != DEF_PRIORITY
branch (seq = lrugen->max_seq) and can evict from the youngest generations
whenever older generations of a type are empty, while reporting priority 0
in trace_mm_vmscan_lru_shrink_inactive().

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=7

Re: [PATCH v7 10/16] mm/mglru: Run aging when pages are rare outside the youngest gen

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [High] mm/mglru: single-word handle used in commit Author and
  Signed-off-by trailer
--

commit e3df19968a61ac9c4f39eb92e538d862f157c5ad
Author: lyugaofei <lyugaofei@xiaomi.com>

> mm/mglru: Run aging when pages are rare outside the youngest gen
>
> Run aging when the total number of pages outside the youngest
> generation across both types falls below 1/MAX_NR_GENS of the number
> of pages in the youngest generation. For extreme swappiness values
> such as 1 and 200, also consider the balance of the corresponding
> type.
>
> This improves reclaim efficiency, especially at extreme swappiness
> values, while reducing system time.
>
> To avoid the overhead of aging, we only allow imbalance-based aging
> when the reclaim priority is low enough that we might reclaim the
> youngest generation.
>
> Signed-off-by: lyugaofei <lyugaofei@xiaomi.com>
> Co-developed-by: Barry Song (Xiaomi) <baohua@kernel.org>
> Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>

[Severity: High]
The Author header and the first Signed-off-by trailer use the single-word
handle "lyugaofei" instead of a full real human name, which does not meet
the Developer's Certificate of Origin requirements in
Documentation/process/submitting-patches.rst.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=10

Re: [PATCH v7 11/16] mm/mglru: Run aging when one type has no populatable folios

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential
issues to consider:
- [High] mm/mglru: skipped aging in try_to_shrink_lruvec() when zero
  folios are scanned
- [Medium] mm/mglru: repeated aging in try_to_shrink_lruvec() when
  no_populatable persists
- [Low] mm/mglru: stale max_seq passed to should_run_aging() in
  try_to_shrink_lruvec()
--

commit b68a220713e0f1b121c4874a48ac05f55108264a
Author: Barry Song (Xiaomi) <baohua@kernel.org>

mm/mglru: Run aging when one type has no populatable folios

This commit moves the aging check in try_to_shrink_lruvec() after
evict_folio_lists() and passes a no_populatable flag to should_run_aging()
so aging runs when one LRU type makes no scan progress despite remaining
scan budget.

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 085450819ee8e..41dd77652c82f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -5105,7 +5105,8 @@ static bool lru_gen_imbalanced(struct lruvec *lruvec, struct scan_control *sc,
>  }
>  
>  static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
> -			     struct scan_control *sc, int swappiness)
> +			     struct scan_control *sc, int swappiness,
> +			     bool no_populatable)
>  {
>  	DEFINE_MIN_SEQ(lruvec);
>  
> @@ -5117,6 +5118,13 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
>  	if (sc->priority == DEF_PRIORITY)
>  		return false;
>  
> +	/*
> +	 * Run aging if scan budget remains but no folios
> +	 * in populatable generations are available to scan.
> +	 */
> +	if (no_populatable)
> +		return true;
> +
>  	/* better to run aging even though eviction is still possible */
>  	if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq)
>  		return true;
> @@ -5221,20 +5229,17 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  	lru_gen_prepare_scan(lruvec, sc, memcg, swappiness, nr);
>  
>  	while (nr[LRU_GEN_ANON] > 0 || nr[LRU_GEN_FILE] > 0) {
> +		unsigned long orig_file, orig_anon;
>  		DEFINE_MAX_SEQ(lruvec);
> +		bool no_populatable;
>  
>  		if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg)) {
>  			need_rotate = true;
>  			break;
>  		}
>  
> -		if (should_run_aging(lruvec, max_seq, sc, swappiness)) {
> -			trace_mm_mglru_aging(lruvec, sc, swappiness);
> -			if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false))
> -				need_rotate = true;
> -			should_age = true;
> -		}
> -
> +		orig_anon = nr[LRU_GEN_ANON];
> +		orig_file = nr[LRU_GEN_FILE];
>  		if (!evict_folio_lists(nr, lruvec, sc, swappiness, MIN_LRU_BATCH))
>  			break;
>  

[Severity: High]
Does moving should_run_aging() and try_to_inc_max_seq() after
evict_folio_lists() skip aging whenever evict_folio_lists() scans zero
folios?

mm/vmscan.c:scan_folios() {
	...
	if (sc->priority == DEF_PRIORITY)
		seq = lrugen->max_seq - MIN_NR_GENS;
	else if (sc->priority > DEF_PRIORITY / 2)
		seq = lrugen->max_seq - 1;
	else
		seq = lrugen->max_seq;

	seq = lruvec_populated_min_seq(lruvec, type, sc->reclaim_idx + 1, seq);
	...
}

At DEF_PRIORITY, when only MIN_NR_GENS generations remain
(evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq),
scan_folios() caps seq to max_seq - MIN_NR_GENS, which is below min_seq
and already empty.  evict_folio_lists() then returns 0 and breaks out of
the loop before reaching should_run_aging(), making the mandatory
evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq aging
check unreachable at DEF_PRIORITY.

Similarly, at DEF_PRIORITY / 2 < sc->priority < DEF_PRIORITY,
scan_folios() caps seq to max_seq - 1.  Whenever all evictable folios for
the budgeted type(s) are in max_seq (for example when both types only have
folios in max_seq, or when only one type has budget left),
evict_folio_lists() returns 0 and breaks before aging can run, leaving
need_rotate false as well so shrink_one() fails to rotate a sizable memcg.

Finally, when sc->priority <= DEF_PRIORITY / 2, running
evict_folio_lists() before should_run_aging() scans directly from max_seq
(where min_gen == max_gen in sort_folio() disables tier protection) before
aging can split the youngest generation, and breaks without aging if the
first batch satisfies should_abort_scan().

> @@ -5248,6 +5253,15 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  		if (root_reclaim(sc) && should_age)
>  			break;
>  
> +		no_populatable = (nr[LRU_GEN_ANON] && nr[LRU_GEN_ANON] == orig_anon) ||
> +				 (nr[LRU_GEN_FILE] && nr[LRU_GEN_FILE] == orig_file);

[Severity: Medium]
Can no_populatable stay true across every MIN_LRU_BATCH iteration and
trigger repeated aging when one type still scans 0 folios after aging?

nr[] is computed once in lru_gen_prepare_scan() and is only decremented by
scanned folios.  If scan_folios() continues to return 0 for one type while
the other type makes progress (for instance when sc->priority <=
DEF_PRIORITY / 2 already scans up to max_seq, when max_seq has no eligible
folios of that type, or when walk_mm() promotes all referenced folios into
the new youngest generation), nr[type] remains equal to orig_anon or
orig_file.  In cgroup reclaim (!root_reclaim(sc)), the loop does not break
on should_age, so should_run_aging() returns true and calls
try_to_inc_max_seq() on every 64-page batch of the other type; in
root_reclaim(sc), it runs unnecessary aging and aborts scanning the
populated type after one extra batch.

> +		if (should_run_aging(lruvec, max_seq, sc, swappiness, no_populatable)) {
> +			trace_mm_mglru_aging(lruvec, sc, swappiness);
> +			if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false))
> +				need_rotate = true;
> +			should_age = true;
> +		}

[Severity: Low]
Can should_run_aging() see a stale max_seq alongside a fresh min_seq here?

DEFINE_MAX_SEQ(lruvec) snapshots max_seq at the start of the loop before
evict_folio_lists(), whereas should_run_aging() reads min_seq after
evict_folio_lists() finishes.  If a concurrent reclaimer advances max_seq
and min_seq during eviction, should_run_aging() compares the new min_seq
against the old max_seq, which can falsely trigger the aging branch, fail
try_to_inc_max_seq() on the stale max_seq, and set should_age = true so
root_reclaim(sc) aborts on the next pass.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=11

Re: [PATCH v7 12/16] mm/mglru: Restrict eviction accounting to eligible zones

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [High] mm/mglru: premature OOM kill in lru_gen_age_node() on
  zone-constrained reclaim
--

commit 169c51ce627ac19052dda882e181615f7e7c984d
Author: Barry Song (Xiaomi) <baohua@kernel.org>

mm/mglru: Restrict eviction accounting to eligible zones

This commit restricts lruvec_evictable_size() and lru_gen_imbalanced() to
count only zones at or below sc->reclaim_idx by adding a max_zone
parameter to lruvec_gen_size().

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 41dd77652c82f..8b77e6bc1d519 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4207,8 +4207,8 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
>  	sc->priority = clamp(priority, DEF_PRIORITY / 2, DEF_PRIORITY);
>  }
>  
> -static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
> -				  unsigned long nr[])
> +static void lruvec_evictable_size(struct lruvec *lruvec, struct scan_control *sc,
> +				  int swappiness, unsigned long nr[])
>  {
>  	int type;
>  	unsigned long seq;
> @@ -4221,7 +4221,7 @@ static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
>  
>  	for_each_evictable_type(type, swappiness) {
>  		for (seq = min_seq[type]; seq <= max_seq; seq++)
> -			nr[type] += lruvec_gen_size(lrugen, type, seq);
> +			nr[type] += lruvec_gen_size(lrugen, type, seq, sc->reclaim_idx + 1);
>  	}
>  }
>  
> @@ -4230,7 +4230,7 @@ static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
>  	unsigned long total, sizes[ANON_AND_FILE];
>  	int swappiness = get_swappiness(lruvec, sc);
>  
> -	lruvec_evictable_size(lruvec, swappiness, sizes);
> +	lruvec_evictable_size(lruvec, sc, swappiness, sizes);
>  	total = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
>  
>  	/* whether the size is big enough to be helpful */

[Severity: High]
Can restricting lruvec_is_sizable() to sc->reclaim_idx trigger a premature
global OOM kill in lru_gen_age_node() during zone-constrained reclaim when
lru_gen_min_ttl is enabled?

In balance_pgdat(), kswapd sets sc.reclaim_idx = highest_zoneidx and runs
kswapd_age_node() -> lru_gen_age_node() before kswapd_shrink_node():

mm/vmscan.c:lru_gen_age_node() {
	...
	do {
		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);

		mem_cgroup_calculate_protection(NULL, memcg);

		if (!reclaimable)
			reclaimable = lruvec_is_reclaimable(lruvec, sc, min_ttl);
	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
	...
	if (!reclaimable && mutex_trylock(&oom_lock)) {
		struct oom_control oc = {
			.gfp_mask = sc->gfp_mask,
		};

		out_of_memory(&oc);

		mutex_unlock(&oom_lock);
	}
}

Because user LRU pages are allocated from the highest zones and kept out of
lower zones by lowmem_reserve, a wakeup with a constrained highest_zoneidx
(such as ZONE_DMA or ZONE_DMA32) can find fewer than 1UL << sc->priority
evictable pages in zones 0..sc->reclaim_idx in every memcg.
lruvec_is_sizable() and lruvec_is_reclaimable() then return false for all
memcgs, causing lru_gen_age_node() to invoke out_of_memory() with
GFP_KERNEL even when higher zones have plenty of reclaimable memory older
than min_ttl.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=12

Re: [PATCH v7 14/16] mm/mglru: Avoid prolonged anon reclaim with swappiness=200

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential
issues to consider:
- [High] mm/mglru: commit Author and Signed-off-by use handle instead of
  real name
- [Medium] mm/mglru: zero sc.priority in run_eviction() skews
  lru_gen_balance_scan()
--

commit 8a29a76d461ffd04769caa1f7ed98ca18efe1fb3
Author: lyugaofei <lyugaofei@xiaomi.com>

> mm/mglru: Avoid prolonged anon reclaim with swappiness=200
>
> It has been observed that swappiness=200 can significantly slow down
> reclaim on some machines, with some workloads running 3x slower
> under MGLRU than under CLRU.
>
> This is because swappiness=200 currently results in file_factor=0.
> Give file reclaim a small factor at lower priorities, for example,
> when sc->priority < DEF_PRIORITY / 2.
>
> Signed-off-by: lyugaofei <lyugaofei@xiaomi.com>
> Co-developed-by: Barry Song (Xiaomi) <baohua@kernel.org>
> Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>

[Severity: High]
Per Documentation/process/submitting-patches.rst, both the commit Author
and the Signed-off-by trailer must use a known real full human name rather
than an account handle ("lyugaofei").

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2030c15c06674..a92b14190d733 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4889,8 +4889,8 @@ static int get_tier_idx(struct lruvec *lruvec, int type)
>   * We don't calculate the scan cost, MGLRU uses lazy promotion, which will
>   * cancel the scan budget natually.
>   */
> -static void lru_gen_balance_scan(struct lruvec *lruvec, int swappiness,
> -		unsigned long total_scan, unsigned long nr[])
> +static void lru_gen_balance_scan(struct lruvec *lruvec, struct scan_control *sc,
> +		int swappiness, unsigned long total_scan, unsigned long nr[])
>  {
>  	struct lru_gen_folio *lrugen = &lruvec->lrugen;
>  	u64 refault_rate[ANON_AND_FILE], anon_factor, file_factor;
> @@ -4947,7 +4947,12 @@ static void lru_gen_balance_scan(struct lruvec *lruvec, int swappiness,
>  	file_weight = nr[LRU_GEN_FILE] + nr[LRU_GEN_ANON] / size_bias;
>  
>  	anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
> -	file_factor = (u64)(MAX_SWAPPINESS - swappiness) * refault_rate[LRU_GEN_ANON] * file_weight;
> +	if (swappiness == MAX_SWAPPINESS)
> +		file_factor = sc->priority < DEF_PRIORITY / 2 ?
> +			      refault_rate[LRU_GEN_ANON] * file_weight : 0;
> +	else
> +		file_factor = (u64)(MAX_SWAPPINESS - swappiness) *
> +			      refault_rate[LRU_GEN_ANON] * file_weight;

[ ... ]

> @@ -5891,7 +5896,7 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
>  			return 0;
>  
>  		lruvec_evictable_size(lruvec, sc, swappiness, nr_to_scan);
> -		lru_gen_balance_scan(lruvec, swappiness,
> +		lru_gen_balance_scan(lruvec, sc, swappiness,
>  				     nr_to_reclaim - sc->nr_reclaimed, nr_to_scan);
>  
>  		if (!evict_folio_lists(nr_to_scan, lruvec, sc, swappiness, MAX_LRU_BATCH))

[Severity: Medium]
Does passing sc from run_eviction() into lru_gen_balance_scan() cause
swappiness=200 via debugfs proactive reclaim to always calculate a non-zero
file_factor?

lru_gen_seq_write() initializes sc on the stack without setting .priority
to DEF_PRIORITY, leaving sc.priority zero-initialized when passed to
run_cmd() -> run_eviction().  In lru_gen_balance_scan(), sc->priority <
DEF_PRIORITY / 2 (0 < 6) is then unconditionally true, so proactive
eviction with swappiness=200 always reclaims file pages instead of
preferring anonymous memory.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=14

Re: [PATCH v7 15/16] mm/mglru: Make swappiness=1 file reclaim more aggressive

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm/mglru: missing sc.priority init for lru_gen_balance_scan()
  via debugfs
--

commit cf50aabb1ef5db31c58a09226fe4dbb55149d981
Author: Barry Song (Xiaomi) <baohua@kernel.org>

mm/mglru: Make swappiness=1 file reclaim more aggressive

This commit sets anon_factor to 0 in lru_gen_balance_scan() when swappiness
is 1 and sc->priority is above DEF_PRIORITY / 2, making file reclaim more
aggressive at normal reclaim priorities.

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a92b14190d733..f36e9a379b62a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4946,7 +4946,11 @@ static void lru_gen_balance_scan(struct lruvec *lruvec, struct scan_control *sc,
>  	anon_weight = nr[LRU_GEN_ANON] + nr[LRU_GEN_FILE] / size_bias;
>  	file_weight = nr[LRU_GEN_FILE] + nr[LRU_GEN_ANON] / size_bias;
>  
> -	anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
> +	if (swappiness == MIN_SWAPPINESS + 1)
> +		anon_factor = sc->priority <= DEF_PRIORITY / 2 ?
> +			      refault_rate[LRU_GEN_FILE] * anon_weight : 0;
> +	else
> +		anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;

[Severity: Low]
Does the sc->priority <= DEF_PRIORITY / 2 check always evaluate to true when
lru_gen_balance_scan() is called from the debugfs eviction path
(lru_gen_seq_write() -> run_cmd() -> run_eviction())?

lru_gen_seq_write() allocates sc on the stack without initializing
.priority, so sc.priority is 0 and anon_factor is never zeroed out for
swappiness=1 during debugfs proactive eviction.  Should lru_gen_seq_write()
initialize .priority = DEF_PRIORITY in sc (as commit "mm/mglru: balance anon
and file scan budget by refault rate" noted in its commit message)?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=15

Re: [PATCH v7 16/16] mm/mglru: Avoid scan anon while swapcache is low for GFP_NOIO allocation

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] mm/mglru: stalled aging in try_to_shrink_lruvec() under
  GFP_NOIO
--

commit c2e07c75b5549aa295c630747e1cecd7625269f0
Author: Bo Zhang <zhangbo56@xiaomi.com>

mm/mglru: Avoid scan anon while swapcache is low for GFP_NOIO allocation

This commit skips anonymous folio scanning in MGLRU when GFP_NOIO is set
and swapcache is low by checking can_reclaim_anon_pages() in
lruvec_evictable_size().

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f36e9a379b62a..4fdbf0c2dcde0 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
[ ... ]
> @@ -4213,6 +4206,8 @@ static void lruvec_evictable_size(struct lruvec *lruvec, struct scan_control *sc
>  	int type;
>  	unsigned long seq;
>  	struct lru_gen_folio *lrugen = &lruvec->lrugen;
> +	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
> +	int nid = lruvec_pgdat(lruvec)->node_id;
>  	DEFINE_MAX_SEQ(lruvec);
>  	DEFINE_MIN_SEQ(lruvec);
>  
> @@ -4220,6 +4215,8 @@ static void lruvec_evictable_size(struct lruvec *lruvec, struct scan_control *sc
>  	nr[LRU_GEN_FILE] = 0;
>  
>  	for_each_evictable_type(type, swappiness) {
> +		if (type == LRU_GEN_ANON && !can_reclaim_anon_pages(memcg, nid, sc))
> +			continue;
>  		for (seq = min_seq[type]; seq <= max_seq; seq++)
>  			nr[type] += lruvec_gen_size(lrugen, type, seq, sc->reclaim_idx + 1);
>  	}

[Severity: Medium]
Can zeroing nr[LRU_GEN_ANON] here while swappiness remains non-zero stall
MGLRU aging during GFP_NOIO reclaim?

When swap space is available and NUMA demotion is not, get_swappiness()
stays in 1..MAX_SWAPPINESS even when can_reclaim_anon_pages() returns
false. Because nr[LRU_GEN_ANON] is 0, evict_folio_lists() only scans file
generations, so min_seq[LRU_GEN_ANON] stays at max_seq - 3 and
try_to_inc_min_seq() clamps min_seq[LRU_GEN_FILE] to max_seq - MIN_NR_GENS:

mm/vmscan.c:try_to_inc_min_seq() {
	...
	if (swappiness && swappiness <= MAX_SWAPPINESS) {
		unsigned long seq = lrugen->max_seq - MIN_NR_GENS;

		if (min_seq[LRU_GEN_ANON] > seq && min_seq[LRU_GEN_FILE] < seq)
			min_seq[LRU_GEN_ANON] = seq;
		else if (min_seq[LRU_GEN_FILE] > seq && min_seq[LRU_GEN_ANON] < seq)
			min_seq[LRU_GEN_FILE] = seq;
	}
}

Once populatable file generations are drained, evict_folio_lists() returns
0 and try_to_shrink_lruvec() breaks out of the loop before setting
no_populatable, while should_run_aging() sees evictable_min_seq() at
min_seq[LRU_GEN_ANON] (max_seq - 3) and lru_gen_imbalanced() still counts
unreclaimable anon pages in old[LRU_GEN_ANON]. As a result, reclaim fails
to age from DEF_PRIORITY down to DEF_PRIORITY / 2 + 1 and then directly
evicts the youngest file generation (max_seq) without page-table aging or
tier protection.

Should get_swappiness() return 0 when !can_reclaim_anon_pages() instead, so
swappiness is 0 consistently across try_to_shrink_lruvec(),
try_to_inc_min_seq(), should_run_aging(), and lru_gen_imbalanced()?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=16

Re: [PATCH v7 02/16] mm/mglru: extract lruvec_populated_min_seq() helper

[Barry Song]

On Thu, Nov 12, 2026 at 1:00 PM <sashiko-bot@kernel.org> wrote:
>
> Thank you for your contribution! Sashiko AI review found 1 potential
> issue to consider:
> - [Low] mm/mglru: shadowed local variable seq in try_to_inc_min_seq()
> --
>
> commit 7a4927e9f0aa8623b1c83f69afd1fb935c342dd5
> Author: Kairui Song <kasong@tencent.com>
>
> mm/mglru: extract lruvec_populated_min_seq() helper
>
> This commit extracts the search for the oldest populated generation of a
> type from try_to_inc_min_seq() into a new lruvec_populated_min_seq()
> helper.
>
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index ed224cb80a75a..f98cd483f014a 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
>
> [ ... ]
>
> >  static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
> >  {
> > -     int gen, type, zone;
> > +     int type;
> >       bool seq_inc_flag = false;
> >       struct lru_gen_folio *lrugen = &lruvec->lrugen;
> >       DEFINE_MIN_SEQ(lruvec);
> > +     unsigned long seq;
> >
> >       VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
> >
> > -     /* find the oldest populated generation */
> > +     /* Requires at least MIN_NR_GENS gens for basic functionality */
> > +     seq = lrugen->max_seq - MIN_NR_GENS;
> >       for_each_evictable_type(type, swappiness) {
> > -             while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) {
> > -                     gen = lru_gen_from_seq(min_seq[type]);
> > -
> > -                     for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> > -                             if (!list_empty(&lrugen->folios[gen][type][zone]))
> > -                                     goto next;
> > -                     }
> > -
> > -                     min_seq[type]++;
> > +             min_seq[type] = lruvec_populated_min_seq(lruvec, type, seq + 1);
> > +             if (min_seq[type] > lrugen->min_seq[type])
> >                       seq_inc_flag = true;
> > -             }
> > -next:
> > -             ;
> >       }
>
> [Severity: Low]
> This isn't a bug, but adding seq at function scope causes the existing
> inner declaration in try_to_inc_min_seq() to shadow it and recompute the
> same value:
>
> mm/vmscan.c:try_to_inc_min_seq() {
>         ...
>         if (swappiness && swappiness <= MAX_SWAPPINESS) {
>                 unsigned long seq = lrugen->max_seq - MIN_NR_GENS;
>         ...
> }
>
> Dropping the inner declaration would avoid the -Wshadow warning under W=2
> and reuse the value already computed.

This makes sense to me, we can do:

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9f759d213614..a640590f6be3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4033,8 +4033,6 @@ static void try_to_inc_min_seq(struct lruvec
*lruvec, int swappiness)

        /* see the comment on lru_gen_folio */
        if (swappiness && swappiness <= MAX_SWAPPINESS) {
-               unsigned long seq = lrugen->max_seq - MIN_NR_GENS;
-
                if (min_seq[LRU_GEN_ANON] > seq && min_seq[LRU_GEN_FILE] < seq)
                        min_seq[LRU_GEN_ANON] = seq;
                else if (min_seq[LRU_GEN_FILE] > seq &&
min_seq[LRU_GEN_ANON] < seq)


>
> --
> Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=2

Re: [PATCH v7 10/16] mm/mglru: Run aging when pages are rare outside the youngest gen

[Barry Song]

On Thu, Nov 12, 2026 at 1:01 PM <sashiko-bot@kernel.org> wrote:
>
> Thank you for your contribution! Sashiko AI review found 1 potential
> issue to consider:
> - [High] mm/mglru: single-word handle used in commit Author and
>   Signed-off-by trailer
> --
>
> commit e3df19968a61ac9c4f39eb92e538d862f157c5ad
> Author: lyugaofei <lyugaofei@xiaomi.com>
>
> > mm/mglru: Run aging when pages are rare outside the youngest gen
> >
> > Run aging when the total number of pages outside the youngest
> > generation across both types falls below 1/MAX_NR_GENS of the number
> > of pages in the youngest generation. For extreme swappiness values
> > such as 1 and 200, also consider the balance of the corresponding
> > type.
> >
> > This improves reclaim efficiency, especially at extreme swappiness
> > values, while reducing system time.
> >
> > To avoid the overhead of aging, we only allow imbalance-based aging
> > when the reclaim priority is low enough that we might reclaim the
> > youngest generation.
> >
> > Signed-off-by: lyugaofei <lyugaofei@xiaomi.com>
> > Co-developed-by: Barry Song (Xiaomi) <baohua@kernel.org>
> > Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
>
> [Severity: High]
> The Author header and the first Signed-off-by trailer use the single-word
> handle "lyugaofei" instead of a full real human name, which does not meet
> the Developer's Certificate of Origin requirements in
> Documentation/process/submitting-patches.rst.

Okay, let me change it to

Gaofei Lyu <lyugaofei@xiaomi.com>

>
> --
> Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=10

Re: [PATCH v7 05/16] mm/mglru: skip zones above reclaim_idx instead of rotating them

[Barry Song]

On Thu, Nov 12, 2026 at 1:01 PM <sashiko-bot@kernel.org> wrote:
>
> Thank you for your contribution! Sashiko AI review found 1 potential
> issue to consider:
> - [High] mm/mglru: pinned min_seq in try_to_inc_min_seq() stalls aging
> --
>
> commit a9558af5b6eefdf9bb9a64058218b290ef8ecc66
> Author: Kairui Song <kasong@tencent.com>
>
> mm/mglru: skip zones above reclaim_idx instead of rotating them
>
> This commit restricts scan_folios() and lruvec_populated_min_seq() to zones up
> to sc->reclaim_idx instead of scanning and rotating folios in higher zones.
>
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 51c2ee66b3ee8..273aa8c56bec8 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -3992,7 +3992,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
> >
> >  /* Similar to lruvec_evictable_size, return the oldest populated seq of the type */
> >  static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
> > -                                           unsigned long max_seq)
> > +                                           int zone_limit, unsigned long max_seq)
> >  {
> >       int gen, zone;
> >       unsigned long min_seq;
> > @@ -4003,7 +4003,7 @@ static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
> >       min_seq = READ_ONCE(lrugen->min_seq[type]);
> >       while (min_seq <= max_seq) {
> >               gen = lru_gen_from_seq(min_seq);
> > -             for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> > +             for (zone = 0; zone < zone_limit; zone++) {
> >                       if (!list_empty(&lrugen->folios[gen][type][zone]))
> >                               return min_seq;
> >               }
> > @@ -4026,7 +4026,7 @@ static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
> >       /* Requires at least MIN_NR_GENS gens for basic functionality */
> >       seq = lrugen->max_seq - MIN_NR_GENS;
> >       for_each_evictable_type(type, swappiness) {
> > -             min_seq[type] = lruvec_populated_min_seq(lruvec, type, seq + 1);
> > +             min_seq[type] = lruvec_populated_min_seq(lruvec, type, MAX_NR_ZONES, seq + 1);
> >               if (min_seq[type] > lrugen->min_seq[type])
> >                       seq_inc_flag = true;
> >       }
>
> [ ... ]
>
> > @@ -4780,24 +4773,22 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
> >        * when under pressure to respect swappiness more and reduce IO cost.
> >        */
> >       if (sc->priority == DEF_PRIORITY)
> > -             min_seq = lrugen->min_seq[type];
> > +             seq = lrugen->min_seq[type];
> >       else
> > -             min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq);
> > +             seq = lrugen->max_seq;
> >
> > -     gen = lru_gen_from_seq(min_seq);
> > +     seq = lruvec_populated_min_seq(lruvec, type, sc->reclaim_idx + 1, seq);
> > +     gen = lru_gen_from_seq(seq);
> >       max_gen = lru_gen_from_seq(max_seq);
> >
> > -     for (i = MAX_NR_ZONES; i > 0; i--) {
> > +     /* Scan eligible zones in descending order. */
> > +     for (zone_idx = sc->reclaim_idx; zone_idx >= 0; zone_idx--) {
>
> [Severity: High]
> As reported by KunWu Chan on RFC v5 [1], does skipping zones above
> sc->reclaim_idx in scan_folios() while try_to_inc_min_seq() still checks all
> MAX_NR_ZONES stall aging during zone-constrained reclaim (for example,
> GFP_DMA32 reclaim when ZONE_NORMAL is populated)?
>
> When an lruvec has MAX_NR_GENS (4) generations, lrugen->min_seq[type] starts
> at max_seq - 3.  Because scan_folios() no longer rotates folios in zones above
> sc->reclaim_idx, any folios in those zones keep try_to_inc_min_seq() from
> advancing lrugen->min_seq[type] once eligible zones are drained.
>
> In should_run_aging():
>
> mm/vmscan.c:should_run_aging() {
>         ...
>         if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq)
>                 return true;
>
>         /* try to avoid aging, do gentle reclaim at the default priority */
>         if (sc->priority == DEF_PRIORITY)
>                 return false;
>
>         /* better to run aging even though eviction is still possible */
>         return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq;
> }
>
> With min_seq pinned at max_seq - 3, evictable_min_seq() + MIN_NR_GENS never
> reaches max_seq, so should_run_aging() returns false and scan_folios() drains
> eligible zones down to the youngest generation max_seq where sort_folio()
> disables tier protection and workingset promotion (min_gen == max_gen).
>
> Even with the follow-up commits in this series (commit "mm/mglru: Run aging
> when pages are rare outside the youngest gen", commit "mm/mglru: Run aging
> when one type has no populatable folios", and commit "mm/mglru: Restrict
> eviction accounting to eligible zones"), at priorities above DEF_PRIORITY / 2
> scan_folios() caps seq at max_seq - 1 and evict_folio_lists() returns 0 once
> older generations are empty in eligible zones, causing try_to_shrink_lruvec()
> to break out before calling should_run_aging() until priority drops to

I'm not sure why this is marked as high severity, as it
seems more like a performance concern. Also, when we
scan the youngest generation, tier protection and
workingset promotion are no longer needed, as the
folios are already in the youngest generation.

Actually, I created a silly test case that forces
GFP_DMA32 for anon folios:

diff --git a/mm/memory.c b/mm/memory.c
index fe72e66c9c2e..350ac4a834e6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1251,7 +1251,7 @@ static inline struct folio
*folio_prealloc(struct mm_struct *src_mm,
        if (need_zero)
                new_folio = vma_alloc_zeroed_movable_folio(vma, addr);
        else
-               new_folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, addr);
+               new_folio = vma_alloc_folio(GFP_USER | __GFP_DMA32, 0,
vma, addr);

        if (!new_folio)
                return NULL;
@@ -5053,7 +5053,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
        if (!folio) {
                /* Swapin bypasses readahead for SWP_SYNCHRONOUS_IO
devices and zswap */
                if (swap_entry_synchronous(si, entry))
-                       folio = swapin_sync(entry, GFP_HIGHUSER_MOVABLE,
+                       folio = swapin_sync(entry,
GFP_HIGHUSER_MOVABLE | __GFP_DMA32,

thp_swapin_suitable_orders(si, vmf) | BIT(0),
                                            vmf, NULL, 0);
                else


In this case, the current patchset still performs much
better on MGLRU than using CLRU.

MGLRU
*** Executing round 0 ***
set swappiness to 60

real 1m57.803s
user 25m34.833s
sys 6m8.024s


CLRU:
*** Executing round 0 ***
set swappiness to 60

Endless....(CLRU can't finish the kernel build at all)

If we do want to trigger aging earlier when evict_folio_lists()
returns 0, rather than waiting until the priority drops to
DEF_PRIORITY / 2, Bo Zhang shared an idea with me off-list
that might address this issue.

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9f759d213614..3721725852b3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4033,8 +4033,6 @@ static void try_to_inc_min_seq(struct lruvec
*lruvec, int swappiness)

        /* see the comment on lru_gen_folio */
        if (swappiness && swappiness <= MAX_SWAPPINESS) {
-               unsigned long seq = lrugen->max_seq - MIN_NR_GENS;
-
                if (min_seq[LRU_GEN_ANON] > seq && min_seq[LRU_GEN_FILE] < seq)
                        min_seq[LRU_GEN_ANON] = seq;
                else if (min_seq[LRU_GEN_FILE] > seq &&
min_seq[LRU_GEN_ANON] < seq)
@@ -5233,6 +5231,7 @@ static bool try_to_shrink_lruvec(struct lruvec
*lruvec, struct scan_control *sc)
                unsigned long orig_file, orig_anon;
                DEFINE_MAX_SEQ(lruvec);
                bool no_populatable;
+               long scanned;

                if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg)) {
                        need_rotate = true;
@@ -5241,8 +5240,7 @@ static bool try_to_shrink_lruvec(struct lruvec
*lruvec, struct scan_control *sc)

                orig_anon = nr[LRU_GEN_ANON];
                orig_file = nr[LRU_GEN_FILE];
-               if (!evict_folio_lists(nr, lruvec, sc, swappiness,
MIN_LRU_BATCH))
-                       break;
+               scanned = evict_folio_lists(nr, lruvec, sc,
swappiness, MIN_LRU_BATCH);

                if (should_abort_scan(lruvec, sc))
                        break;
@@ -5263,6 +5261,9 @@ static bool try_to_shrink_lruvec(struct lruvec
*lruvec, struct scan_control *sc)
                        should_age = true;
                }

+               if (!scanned)
+                       break;
+
                cond_resched();
        }

> DEF_PRIORITY / 2 and scans max_seq without tier protection.
>
> [1] https://lore.kernel.org/r/CAN_Opa-AScm9=EeXO_Uy8VjbQ=bqY9P++rFP8H1RhUB4dOt6xw@mail.gmail.com
>
> --
> Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=5

Re: [PATCH v7 12/16] mm/mglru: Restrict eviction accounting to eligible zones

[Barry Song]

On Thu, Nov 12, 2026 at 1:01 PM <sashiko-bot@kernel.org> wrote:
>
> Thank you for your contribution! Sashiko AI review found 1 potential
> issue to consider:
> - [High] mm/mglru: premature OOM kill in lru_gen_age_node() on
>   zone-constrained reclaim
> --
>
> commit 169c51ce627ac19052dda882e181615f7e7c984d
> Author: Barry Song (Xiaomi) <baohua@kernel.org>
>
> mm/mglru: Restrict eviction accounting to eligible zones
>
> This commit restricts lruvec_evictable_size() and lru_gen_imbalanced() to
> count only zones at or below sc->reclaim_idx by adding a max_zone
> parameter to lruvec_gen_size().
>
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 41dd77652c82f..8b77e6bc1d519 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -4207,8 +4207,8 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
> >       sc->priority = clamp(priority, DEF_PRIORITY / 2, DEF_PRIORITY);
> >  }
> >
> > -static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
> > -                               unsigned long nr[])
> > +static void lruvec_evictable_size(struct lruvec *lruvec, struct scan_control *sc,
> > +                               int swappiness, unsigned long nr[])
> >  {
> >       int type;
> >       unsigned long seq;
> > @@ -4221,7 +4221,7 @@ static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
> >
> >       for_each_evictable_type(type, swappiness) {
> >               for (seq = min_seq[type]; seq <= max_seq; seq++)
> > -                     nr[type] += lruvec_gen_size(lrugen, type, seq);
> > +                     nr[type] += lruvec_gen_size(lrugen, type, seq, sc->reclaim_idx + 1);
> >       }
> >  }
> >
> > @@ -4230,7 +4230,7 @@ static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
> >       unsigned long total, sizes[ANON_AND_FILE];
> >       int swappiness = get_swappiness(lruvec, sc);
> >
> > -     lruvec_evictable_size(lruvec, swappiness, sizes);
> > +     lruvec_evictable_size(lruvec, sc, swappiness, sizes);
> >       total = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
> >
> >       /* whether the size is big enough to be helpful */
>
> [Severity: High]
> Can restricting lruvec_is_sizable() to sc->reclaim_idx trigger a premature
> global OOM kill in lru_gen_age_node() during zone-constrained reclaim when
> lru_gen_min_ttl is enabled?
>
> In balance_pgdat(), kswapd sets sc.reclaim_idx = highest_zoneidx and runs
> kswapd_age_node() -> lru_gen_age_node() before kswapd_shrink_node():
>
> mm/vmscan.c:lru_gen_age_node() {
>         ...
>         do {
>                 struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
>
>                 mem_cgroup_calculate_protection(NULL, memcg);
>
>                 if (!reclaimable)
>                         reclaimable = lruvec_is_reclaimable(lruvec, sc, min_ttl);
>         } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
>         ...
>         if (!reclaimable && mutex_trylock(&oom_lock)) {
>                 struct oom_control oc = {
>                         .gfp_mask = sc->gfp_mask,
>                 };
>
>                 out_of_memory(&oc);
>
>                 mutex_unlock(&oom_lock);
>         }
> }
>
> Because user LRU pages are allocated from the highest zones and kept out of
> lower zones by lowmem_reserve, a wakeup with a constrained highest_zoneidx
> (such as ZONE_DMA or ZONE_DMA32) can find fewer than 1UL << sc->priority
> evictable pages in zones 0..sc->reclaim_idx in every memcg.
> lruvec_is_sizable() and lruvec_is_reclaimable() then return false for all
> memcgs, causing lru_gen_age_node() to invoke out_of_memory() with
> GFP_KERNEL even when higher zones have plenty of reclaimable memory older
> than min_ttl.

I think this is a pre-existing issue. lruvec_is_reclaimable()
uses the current sc->priority to estimate the reclaimable
size, which can significantly underestimate it in min_ttl
cases. Our patch somehow amplifies the problem because it
uses the correct reclaim_idx to calculate the reclaimable
size.

static bool lruvec_is_reclaimable(struct lruvec *lruvec, struct
scan_control *sc,
                                  unsigned long min_ttl)
{
        int gen;
        unsigned long birth;
        int swappiness = get_swappiness(lruvec, sc);
        struct mem_cgroup *memcg = lruvec_memcg(lruvec);
        DEFINE_MIN_SEQ(lruvec);

        if (mem_cgroup_below_min(NULL, memcg))
                return false;

        if (!lruvec_is_sizable(lruvec, sc))
                return false;

        gen = lru_gen_from_seq(evictable_min_seq(min_seq, swappiness));
        birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);

        return time_is_before_jiffies(birth + min_ttl);
}

I think we have two options: either drop this check and
make sure lruvec_is_reclaimable() focuses solely on
min_ttl:

if (!lruvec_is_sizable(lruvec, sc))
        return false;

Or we can do the following, using the lowest possible
kswapd sc->priority to estimate the reclaimable size:

@@ -4245,7 +4243,7 @@ static bool lruvec_is_reclaimable(struct lruvec
*lruvec, struct scan_control *sc
        if (mem_cgroup_below_min(NULL, memcg))
                return false;

-       if (!lruvec_is_sizable(lruvec, sc))
+       if (sc->priority <= 1 && !lruvec_is_sizable(lruvec, sc))
                return false;

        gen = lru_gen_from_seq(evictable_min_seq(min_seq, swappiness));


>
> --
> Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=12