[PATCH v2 0/2] mm: multi-gen LRU: replace get_lruvec() with mem_cgroup_lruvec()

[PATCH v2 0/2] mm: multi-gen LRU: replace get_lruvec() with mem_cgroup_lruvec()

[Siddharth Chintamaneni]

This series cleans up MGLRU's get_lruvec() helper in mm/vmscan.c.

Patch 1 updates get_lruvec() to delegate to mem_cgroup_lruvec() rather
than returning &pgdat->__lruvec directly when memcg is disabled on the
kernel command line.

Patch 2 removes get_lruvec() completely and replaces all 15 call sites
with mem_cgroup_lruvec().

Siddharth Chintamaneni (2):
  mm: multi-gen LRU: use mem_cgroup_lruvec() in get_lruvec()
  mm: multi-gen LRU: remove get_lruvec()

 mm/vmscan.c | 50 +++++++++++++++-----------------------------------
 1 file changed, 15 insertions(+), 35 deletions(-)

-- 
2.45.4

[PATCH v2 1/2] mm: multi-gen LRU: use mem_cgroup_lruvec() in get_lruvec()

[Siddharth Chintamaneni]

Andrew Morton noted that get_lruvec() has the same pattern as
lru_gen_shrink_node(): when memcg is disabled on the command line
(cgroup_disable=memory), it returns &pgdat->__lruvec directly instead of
going through mem_cgroup_lruvec(), which initializes lruvec->pgdat.

In practice all callers of get_lruvec() run after kswapd_init() has
already initialized pgdat->__lruvec.pgdat on every N_MEMORY node, so
this is not a runtime bug. Have get_lruvec() delegate to
mem_cgroup_lruvec() directly.

Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
---
 mm/vmscan.c | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0c57e4f1eb15..99e9f07fa2e1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2745,20 +2745,9 @@ static struct lruvec *get_lruvec(struct mem_cgroup *memcg, int nid)
 {
 	struct pglist_data *pgdat = NODE_DATA(nid);
 
-#ifdef CONFIG_MEMCG
-	if (memcg) {
-		struct lruvec *lruvec = &memcg->nodeinfo[nid]->lruvec;
-
-		/* see the comment in mem_cgroup_lruvec() */
-		if (!lruvec->pgdat)
-			lruvec->pgdat = pgdat;
-
-		return lruvec;
-	}
-#endif
-	VM_WARN_ON_ONCE(!mem_cgroup_disabled());
+	VM_WARN_ON_ONCE(!memcg && !mem_cgroup_disabled());
 
-	return &pgdat->__lruvec;
+	return mem_cgroup_lruvec(memcg, pgdat);
 }
 
 static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc)
-- 
2.45.4

Re: [PATCH v2 1/2] mm: multi-gen LRU: use mem_cgroup_lruvec() in get_lruvec()

[Barry Song]

On Tue, Oct 27, 2026 at 4:23 AM Siddharth Chintamaneni
<sidchintamaneni@gmail.com> wrote:
>
> Andrew Morton noted that get_lruvec() has the same pattern as
> lru_gen_shrink_node(): when memcg is disabled on the command line
> (cgroup_disable=memory), it returns &pgdat->__lruvec directly instead of
> going through mem_cgroup_lruvec(), which initializes lruvec->pgdat.
>
> In practice all callers of get_lruvec() run after kswapd_init() has
> already initialized pgdat->__lruvec.pgdat on every N_MEMORY node, so
> this is not a runtime bug. Have get_lruvec() delegate to
> mem_cgroup_lruvec() directly.

Somehow, I feel this changelog is a bit weird. The earlier
description doesn't really justify the final sentence:
"Have get_lruvec() delegate to mem_cgroup_lruvec() directly."

Can we change it to the below?

The patch was initially developed to address a possible NULL
reference [1].

Andrew Morton reported that get_lruvec() has the same problem as
lru_gen_shrink_node(): when memcg is disabled on the command line
(cgroup_disable=memory), it returns &pgdat->__lruvec directly and so
bypasses the initialization of lruvec->pgdat. The MGLRU debugfs
interface calls get_lruvec(), then dereferences the pgdat pointer in
lru_gen_seq_show() and other paths, so these can hit the same NULL
dereference.

In practice, we found that this cannot happen, as all callers of
get_lruvec() run after kswapd_init() has initialized
pgdat->__lruvec.pgdat on every N_MEMORY node. Therefore, this
is not a runtime bug.

However, it would still be good to clean up get_lruvec() by
removing the MGLRU-specific code and having it delegate
directly to mem_cgroup_lruvec().

[1] https://lore.kernel.org/linux-mm/20261017050928.128582-2-sidchintamaneni@gmail.com/

>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
> Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
> ---

With the changelog updated as suggested,

Reviewed-by: Barry Song <baohua@kernel.org>

Re: [PATCH v2 1/2] mm: multi-gen LRU: use mem_cgroup_lruvec() in get_lruvec()

[Andrew Morton]

On Tue, 3 Nov 2026 06:51:19 +0800 Barry Song <baohua@kernel.org> wrote:

> On Tue, Oct 27, 2026 at 4:23 AM Siddharth Chintamaneni
> <sidchintamaneni@gmail.com> wrote:
> >
> > Andrew Morton noted that get_lruvec() has the same pattern as
> > lru_gen_shrink_node(): when memcg is disabled on the command line
> > (cgroup_disable=memory), it returns &pgdat->__lruvec directly instead of
> > going through mem_cgroup_lruvec(), which initializes lruvec->pgdat.
> >
> > In practice all callers of get_lruvec() run after kswapd_init() has
> > already initialized pgdat->__lruvec.pgdat on every N_MEMORY node, so
> > this is not a runtime bug. Have get_lruvec() delegate to
> > mem_cgroup_lruvec() directly.
> 
> Somehow, I feel this changelog is a bit weird. The earlier
> description doesn't really justify the final sentence:
> "Have get_lruvec() delegate to mem_cgroup_lruvec() directly."
> 
> Can we change it to the below?
> 
> The patch was initially developed to address a possible NULL
> reference [1].
> 
> Andrew Morton reported that get_lruvec() has the same problem as
> lru_gen_shrink_node(): when memcg is disabled on the command line
> (cgroup_disable=memory), it returns &pgdat->__lruvec directly and so
> bypasses the initialization of lruvec->pgdat. The MGLRU debugfs
> interface calls get_lruvec(), then dereferences the pgdat pointer in
> lru_gen_seq_show() and other paths, so these can hit the same NULL
> dereference.
> 
> In practice, we found that this cannot happen, as all callers of
> get_lruvec() run after kswapd_init() has initialized
> pgdat->__lruvec.pgdat on every N_MEMORY node. Therefore, this
> is not a runtime bug.
> 
> However, it would still be good to clean up get_lruvec() by
> removing the MGLRU-specific code and having it delegate
> directly to mem_cgroup_lruvec().
> 
> [1] https://lore.kernel.org/linux-mm/20261017050928.128582-2-sidchintamaneni@gmail.com/

Thanks, I locally made that change.


From: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Subject: mm: multi-gen LRU: use mem_cgroup_lruvec() in get_lruvec()
Date: Mon, 26 Oct 2026 20:23:12 +0000

Patch series "mm: multi-gen LRU: replace get_lruvec() with
mem_cgroup_lruvec()", v2.

This series cleans up MGLRU's get_lruvec() helper in mm/vmscan.c.

Patch 1 updates get_lruvec() to delegate to mem_cgroup_lruvec() rather
than returning &pgdat->__lruvec directly when memcg is disabled on the
kernel command line.

Patch 2 removes get_lruvec() completely and replaces all 15 call sites
with mem_cgroup_lruvec().


This patch (of 2):

The patch was initially developed to address a possible NULL reference
[1].

Andrew Morton reported that get_lruvec() has the same problem as
lru_gen_shrink_node(): when memcg is disabled on the command line
(cgroup_disable=memory), it returns &pgdat->__lruvec directly and so
bypasses the initialization of lruvec->pgdat.  The MGLRU debugfs interface
calls get_lruvec(), then dereferences the pgdat pointer in
lru_gen_seq_show() and other paths, so these can hit the same NULL
dereference.

In practice, we found that this cannot happen, as all callers of
get_lruvec() run after kswapd_init() has initialized pgdat->__lruvec.pgdat
on every N_MEMORY node.  Therefore, this is not a runtime bug.

However, it would still be good to clean up get_lruvec() by removing the
MGLRU-specific code and having it delegate directly to
mem_cgroup_lruvec().

Link: https://lore.kernel.org/20261026202313.63122-1-sidchintamaneni@gmail.com
Link: https://lore.kernel.org/20261026202313.63122-2-sidchintamaneni@gmail.com
Link: https://lore.kernel.org/linux-mm/20261017050928.128582-2-sidchintamaneni@gmail.com/ [1]
Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <apais@microsoft.com>
Cc: <rlmenge@gmail.com>
---

 mm/vmscan.c |   15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

--- a/mm/vmscan.c~mm-multi-gen-lru-use-mem_cgroup_lruvec-in-get_lruvec
+++ a/mm/vmscan.c
@@ -2866,20 +2866,9 @@ static struct lruvec *get_lruvec(struct
 {
 	struct pglist_data *pgdat = NODE_DATA(nid);
 
-#ifdef CONFIG_MEMCG
-	if (memcg) {
-		struct lruvec *lruvec = &memcg->nodeinfo[nid]->lruvec;
+	VM_WARN_ON_ONCE(!memcg && !mem_cgroup_disabled());
 
-		/* see the comment in mem_cgroup_lruvec() */
-		if (!lruvec->pgdat)
-			lruvec->pgdat = pgdat;
-
-		return lruvec;
-	}
-#endif
-	VM_WARN_ON_ONCE(!mem_cgroup_disabled());
-
-	return &pgdat->__lruvec;
+	return mem_cgroup_lruvec(memcg, pgdat);
 }
 
 static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc)
_

[PATCH v2 2/2] mm: multi-gen LRU: remove get_lruvec()

[Siddharth Chintamaneni]

get_lruvec() was originally introduced in commit ec1c86b25f4b ("mm:
multi-gen LRU: groundwork") to guard against NULL NODE_DATA(nid) on
uninitialized NUMA nodes (`return pgdat ? &pgdat->__lruvec : NULL;`).
After commit 09f49dca570a ("mm: handle uninitialized numa nodes
gracefully") and commit 931b6a8b36a2 ("mm: multi-gen LRU: remove NULL
checks on NODE_DATA()"), that NULL check was removed, leaving
get_lruvec() as a thin wrapper around mem_cgroup_lruvec().

Remove get_lruvec() and call mem_cgroup_lruvec() directly at all call
sites.

Suggested-by: Barry Song <baohua@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
---
 mm/vmscan.c | 39 +++++++++++++++------------------------
 1 file changed, 15 insertions(+), 24 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 99e9f07fa2e1..5767b94fd8e8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2741,15 +2741,6 @@ static bool should_clear_pmd_young(void)
 #define get_memcg_gen(seq)	((seq) % MEMCG_NR_GENS)
 #define get_memcg_bin(bin)	((bin) % MEMCG_NR_BINS)
 
-static struct lruvec *get_lruvec(struct mem_cgroup *memcg, int nid)
-{
-	struct pglist_data *pgdat = NODE_DATA(nid);
-
-	VM_WARN_ON_ONCE(!memcg && !mem_cgroup_disabled());
-
-	return mem_cgroup_lruvec(memcg, pgdat);
-}
-
 static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc)
 {
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
@@ -2942,7 +2933,7 @@ void lru_gen_add_mm(struct mm_struct *mm)
 	spin_lock(&mm_list->lock);
 
 	for_each_node_state(nid, N_MEMORY) {
-		struct lruvec *lruvec = get_lruvec(memcg, nid);
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 		struct lru_gen_mm_state *mm_state = get_mm_state(lruvec);
 
 		/* the first addition since the last iteration */
@@ -2972,7 +2963,7 @@ void lru_gen_del_mm(struct mm_struct *mm)
 	spin_lock(&mm_list->lock);
 
 	for_each_node(nid) {
-		struct lruvec *lruvec = get_lruvec(memcg, nid);
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 		struct lru_gen_mm_state *mm_state = get_mm_state(lruvec);
 
 		/* where the current iteration continues after */
@@ -4424,7 +4415,7 @@ void lru_gen_online_memcg(struct mem_cgroup *memcg)
 
 	for_each_node(nid) {
 		struct pglist_data *pgdat = NODE_DATA(nid);
-		struct lruvec *lruvec = get_lruvec(memcg, nid);
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
 
 		spin_lock_irq(&pgdat->memcg_lru.lock);
 
@@ -4446,7 +4437,7 @@ void lru_gen_offline_memcg(struct mem_cgroup *memcg)
 	int nid;
 
 	for_each_node(nid) {
-		struct lruvec *lruvec = get_lruvec(memcg, nid);
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 
 		lru_gen_rotate_memcg(lruvec, MEMCG_LRU_OLD);
 	}
@@ -4459,7 +4450,7 @@ void lru_gen_release_memcg(struct mem_cgroup *memcg)
 
 	for_each_node(nid) {
 		struct pglist_data *pgdat = NODE_DATA(nid);
-		struct lruvec *lruvec = get_lruvec(memcg, nid);
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
 
 		spin_lock_irq(&pgdat->memcg_lru.lock);
 
@@ -4480,7 +4471,7 @@ void lru_gen_release_memcg(struct mem_cgroup *memcg)
 
 void lru_gen_soft_reclaim(struct mem_cgroup *memcg, int nid)
 {
-	struct lruvec *lruvec = get_lruvec(memcg, nid);
+	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 
 	/* see the comment on MEMCG_NR_GENS */
 	if (READ_ONCE(lruvec->lrugen.seg) != MEMCG_LRU_HEAD)
@@ -4489,7 +4480,7 @@ void lru_gen_soft_reclaim(struct mem_cgroup *memcg, int nid)
 
 bool recheck_lru_gen_max_memcg(struct mem_cgroup *memcg, int nid)
 {
-	struct lruvec *lruvec = get_lruvec(memcg, nid);
+	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 	int type;
 
 	for (type = 0; type < ANON_AND_FILE; type++) {
@@ -4536,7 +4527,7 @@ static void try_to_inc_max_seq_nowalk(struct mem_cgroup *memcg,
  */
 void max_lru_gen_memcg(struct mem_cgroup *memcg, int nid)
 {
-	struct lruvec *lruvec = get_lruvec(memcg, nid);
+	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 	int type;
 
 	for (type = 0; type < ANON_AND_FILE; type++) {
@@ -4613,8 +4604,8 @@ void lru_gen_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent,
 	struct zone *zone;
 	enum lru_list lru;
 
-	child_lruvec = get_lruvec(memcg, nid);
-	parent_lruvec = get_lruvec(parent, nid);
+	child_lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+	parent_lruvec = mem_cgroup_lruvec(parent, NODE_DATA(nid));
 
 	for_each_managed_zone_pgdat(zone, NODE_DATA(nid), zid, MAX_NR_ZONES - 1)
 		for (type = 0; type < ANON_AND_FILE; type++)
@@ -5370,7 +5361,7 @@ static void lru_gen_change_state(bool enabled)
 		int nid;
 
 		for_each_node(nid) {
-			struct lruvec *lruvec = get_lruvec(memcg, nid);
+			struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 
 			lruvec_lock_irq(lruvec);
 
@@ -5501,7 +5492,7 @@ static void *lru_gen_seq_start(struct seq_file *m, loff_t *pos)
 
 		for_each_node_state(nid, N_MEMORY) {
 			if (!nr_to_skip--)
-				return get_lruvec(memcg, nid);
+				return mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 		}
 	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
 
@@ -5533,7 +5524,7 @@ static void *lru_gen_seq_next(struct seq_file *m, void *v, loff_t *pos)
 		nid = first_memory_node;
 	}
 
-	return get_lruvec(memcg, nid);
+	return mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 }
 
 static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
@@ -5715,7 +5706,7 @@ static int run_cmd(char cmd, u64 memcg_id, int nid, unsigned long seq,
 		goto done;
 
 	sc->target_mem_cgroup = memcg;
-	lruvec = get_lruvec(memcg, nid);
+	lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 
 	if (swappiness < MIN_SWAPPINESS)
 		swappiness = get_swappiness(lruvec, sc);
@@ -5899,7 +5890,7 @@ void lru_gen_exit_memcg(struct mem_cgroup *memcg)
 	VM_WARN_ON_ONCE(mm_list && !list_empty(&mm_list->fifo));
 
 	for_each_node(nid) {
-		struct lruvec *lruvec = get_lruvec(memcg, nid);
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 		struct lru_gen_mm_state *mm_state = get_mm_state(lruvec);
 
 		VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0,
-- 
2.45.4

Re: [PATCH v2 2/2] mm: multi-gen LRU: remove get_lruvec()

[Barry Song]

On Tue, Oct 27, 2026 at 4:23 AM Siddharth Chintamaneni
<sidchintamaneni@gmail.com> wrote:
>
> get_lruvec() was originally introduced in commit ec1c86b25f4b ("mm:
> multi-gen LRU: groundwork") to guard against NULL NODE_DATA(nid) on
> uninitialized NUMA nodes (`return pgdat ? &pgdat->__lruvec : NULL;`).
> After commit 09f49dca570a ("mm: handle uninitialized numa nodes
> gracefully") and commit 931b6a8b36a2 ("mm: multi-gen LRU: remove NULL
> checks on NODE_DATA()"), that NULL check was removed, leaving
> get_lruvec() as a thin wrapper around mem_cgroup_lruvec().
>
> Remove get_lruvec() and call mem_cgroup_lruvec() directly at all call
> sites.
>
> Suggested-by: Barry Song <baohua@kernel.org>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
> Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
> ---

It's great to see the MGLRU-specific get_lruvec() gone. Thanks!
Hopefully, we can get rid of more MGLRU-specific code,
such as get_swappiness().

Reviewed-by: Barry Song <baohua@kernel.org>

Re: [PATCH v2 2/2] mm: multi-gen LRU: remove get_lruvec()

[Siddharth Chintamaneni]

On Mon, 2 Nov 2026 at 14:56, Barry Song <baohua@kernel.org> wrote:
>
> On Tue, Oct 27, 2026 at 4:23 AM Siddharth Chintamaneni
> <sidchintamaneni@gmail.com> wrote:
> >
> > get_lruvec() was originally introduced in commit ec1c86b25f4b ("mm:
> > multi-gen LRU: groundwork") to guard against NULL NODE_DATA(nid) on
> > uninitialized NUMA nodes (`return pgdat ? &pgdat->__lruvec : NULL;`).
> > After commit 09f49dca570a ("mm: handle uninitialized numa nodes
> > gracefully") and commit 931b6a8b36a2 ("mm: multi-gen LRU: remove NULL
> > checks on NODE_DATA()"), that NULL check was removed, leaving
> > get_lruvec() as a thin wrapper around mem_cgroup_lruvec().
> >
> > Remove get_lruvec() and call mem_cgroup_lruvec() directly at all call
> > sites.
> >
> > Suggested-by: Barry Song <baohua@kernel.org>
> > Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> > Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
> > Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
> > ---
>
> It's great to see the MGLRU-specific get_lruvec() gone. Thanks!
> Hopefully, we can get rid of more MGLRU-specific code,
> such as get_swappiness().
>

I just looked into removing get_swappiness() in favor of its LRU variant
(sc_swappiness()). Do you mean moving the additional conditionals
directly into the callsites?

something like this -
<AI Suggested>

diff --git a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2761,25 +2761,6 @@ static struct lruvec *get_lruvec(struct
mem_cgroup *memcg, int nid)
  return &pgdat->__lruvec;
 }

-static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc)
-{
- struct mem_cgroup *memcg = lruvec_memcg(lruvec);
- struct pglist_data *pgdat = lruvec_pgdat(lruvec);
- int swappiness = sc_swappiness(sc, memcg);
-
- if (swappiness == SWAPPINESS_ANON_ONLY)
- return swappiness;
-
- if (!sc->may_swap)
- return 0;
-
- if (!can_demote(pgdat->node_id, sc, memcg) &&
-    mem_cgroup_get_nr_swap_pages(memcg) < MIN_LRU_BATCH)
- return 0;
-
- return swappiness;
-}
-
 static int get_nr_gens(struct lruvec *lruvec, int type)
 {
  return lruvec->lrugen.max_seq - lruvec->lrugen.min_seq[type] + 1;
@@ -4173,8 +4154,13 @@ static unsigned long
lruvec_evictable_size(struct lruvec *lruvec, int swappiness
 static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
 {
  unsigned long total;
- int swappiness = get_swappiness(lruvec, sc);
  struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+ struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+ int swappiness = sc_swappiness(sc, memcg);
+
+ if (swappiness != SWAPPINESS_ANON_ONLY &&
+    (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)))
+ swappiness = 0;


> Reviewed-by: Barry Song <baohua@kernel.org>

Re: [PATCH v2 2/2] mm: multi-gen LRU: remove get_lruvec()

[Barry Song]

On Tue, Nov 3, 2026 at 7:35 AM Siddharth Chintamaneni
<sidchintamaneni@gmail.com> wrote:
>
> On Mon, 2 Nov 2026 at 14:56, Barry Song <baohua@kernel.org> wrote:
> >
> > On Tue, Oct 27, 2026 at 4:23 AM Siddharth Chintamaneni
> > <sidchintamaneni@gmail.com> wrote:
> > >
> > > get_lruvec() was originally introduced in commit ec1c86b25f4b ("mm:
> > > multi-gen LRU: groundwork") to guard against NULL NODE_DATA(nid) on
> > > uninitialized NUMA nodes (`return pgdat ? &pgdat->__lruvec : NULL;`).
> > > After commit 09f49dca570a ("mm: handle uninitialized numa nodes
> > > gracefully") and commit 931b6a8b36a2 ("mm: multi-gen LRU: remove NULL
> > > checks on NODE_DATA()"), that NULL check was removed, leaving
> > > get_lruvec() as a thin wrapper around mem_cgroup_lruvec().
> > >
> > > Remove get_lruvec() and call mem_cgroup_lruvec() directly at all call
> > > sites.
> > >
> > > Suggested-by: Barry Song <baohua@kernel.org>
> > > Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> > > Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
> > > Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
> > > ---
> >
> > It's great to see the MGLRU-specific get_lruvec() gone. Thanks!
> > Hopefully, we can get rid of more MGLRU-specific code,
> > such as get_swappiness().
> >
>
> I just looked into removing get_swappiness() in favor of its LRU variant
> (sc_swappiness()). Do you mean moving the additional conditionals
> directly into the callsites?

Nop. In MGLRU, swappiness has values: 0, 1–200,
and 201.

With swappiness=0, MGLRU only reclaims file pages and
doesn't care about the hotness of anon pages.

With swappiness=201, MGLRU only reclaims anon pages and
doesn't care about the hotness of file pages.

In both cases, we allow cold/hot inversions in
inc_min_seq(), which can help reduce CPU usage:

static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
{

        /* For file type, skip the check if swappiness is anon only */
        if (type && (swappiness == SWAPPINESS_ANON_ONLY))
                goto done;

        /* For anon type, skip the check if swappiness is zero (file only) */
        if (!type && !swappiness)
                goto done;
       ...
}

Then we could have cases where swappiness is 1 ~ 200, but
we still cannot reclaim anon due to:

1. Swap is full, or the memcg's swap quota is exhausted.

2. The allocation uses GFP_NOIO, but the swap cache is low
[1].

So right now, we have to hack get_swappiness() to return 0
to ensure that reclaim only happens on file pages, or we at
least need to hack reclamation path to use swappiness=0.

This is quite bad, as it can cause cold/hot inversions for
anon pages. I believe this is already a bug in the current
get_swappiness() implementation when swap is full.

Ideally, swappiness values from 1 to 200 and the reclaimable
type should be orthogonal; they should not be coupled.

In other words, we shouldn't need to force swappiness=0 to
reclaim only file pages. If swappiness is set to 60, it
should remain 60 across all MGLRU reclaim paths. The
reclaimable type should be handled separately, without
forcing swappiness to 0 and introducing confusion and bugs.

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

Best,
Barry

Re: [PATCH v2 2/2] mm: multi-gen LRU: remove get_lruvec()

[Siddharth Chintamaneni]

On Mon, 2 Nov 2026 at 16:20, Barry Song <baohua@kernel.org> wrote:
>
> On Tue, Nov 3, 2026 at 7:35 AM Siddharth Chintamaneni
> <sidchintamaneni@gmail.com> wrote:
> >
> > On Mon, 2 Nov 2026 at 14:56, Barry Song <baohua@kernel.org> wrote:
> > >
> > > On Tue, Oct 27, 2026 at 4:23 AM Siddharth Chintamaneni
> > > <sidchintamaneni@gmail.com> wrote:
> > > >
> > > > get_lruvec() was originally introduced in commit ec1c86b25f4b ("mm:
> > > > multi-gen LRU: groundwork") to guard against NULL NODE_DATA(nid) on
> > > > uninitialized NUMA nodes (`return pgdat ? &pgdat->__lruvec : NULL;`).
> > > > After commit 09f49dca570a ("mm: handle uninitialized numa nodes
> > > > gracefully") and commit 931b6a8b36a2 ("mm: multi-gen LRU: remove NULL
> > > > checks on NODE_DATA()"), that NULL check was removed, leaving
> > > > get_lruvec() as a thin wrapper around mem_cgroup_lruvec().
> > > >
> > > > Remove get_lruvec() and call mem_cgroup_lruvec() directly at all call
> > > > sites.
> > > >
> > > > Suggested-by: Barry Song <baohua@kernel.org>
> > > > Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> > > > Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
> > > > Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
> > > > ---
> > >
> > > It's great to see the MGLRU-specific get_lruvec() gone. Thanks!
> > > Hopefully, we can get rid of more MGLRU-specific code,
> > > such as get_swappiness().
> > >
> >
> > I just looked into removing get_swappiness() in favor of its LRU variant
> > (sc_swappiness()). Do you mean moving the additional conditionals
> > directly into the callsites?
>
> Nop. In MGLRU, swappiness has values: 0, 1–200,
> and 201.
>
> With swappiness=0, MGLRU only reclaims file pages and
> doesn't care about the hotness of anon pages.
>
> With swappiness=201, MGLRU only reclaims anon pages and
> doesn't care about the hotness of file pages.
>
> In both cases, we allow cold/hot inversions in
> inc_min_seq(), which can help reduce CPU usage:
>
> static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
> {
>
>         /* For file type, skip the check if swappiness is anon only */
>         if (type && (swappiness == SWAPPINESS_ANON_ONLY))
>                 goto done;
>
>         /* For anon type, skip the check if swappiness is zero (file only) */
>         if (!type && !swappiness)
>                 goto done;
>        ...
> }
>

Interesting!

> Then we could have cases where swappiness is 1 ~ 200, but
> we still cannot reclaim anon due to:
>
> 1. Swap is full, or the memcg's swap quota is exhausted.
>
> 2. The allocation uses GFP_NOIO, but the swap cache is low
> [1].
>
> So right now, we have to hack get_swappiness() to return 0
> to ensure that reclaim only happens on file pages, or we at
> least need to hack reclamation path to use swappiness=0.
>
> This is quite bad, as it can cause cold/hot inversions for
> anon pages. I believe this is already a bug in the current
> get_swappiness() implementation when swap is full.
>
> Ideally, swappiness values from 1 to 200 and the reclaimable
> type should be orthogonal; they should not be coupled.
>
> In other words, we shouldn't need to force swappiness=0 to
> reclaim only file pages. If swappiness is set to 60, it
> should remain 60 across all MGLRU reclaim paths. The
> reclaimable type should be handled separately, without
> forcing swappiness to 0 and introducing confusion and bugs.
>

This is more involved than I initially thought. Let me play around
with it a bit and come back.
If you have any suggestions with experiments that I could run to get a
good understanding on this problem, let me know.

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