[PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Ridong]

From: Ridong Chen <chenridong@xiaomi.com>

sc_swappiness() had two separate definitions depending on
CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
vm_swappiness, ignoring the proactive_swappiness value passed
through scan_control. This caused the swappiness parameter
written to /sys/devices/system/node/nodeX/reclaim to have no
effect when CONFIG_MEMCG is disabled.

Fix this by consolidating sc_swappiness() into a single definition
that checks sc->proactive_swappiness first, then falls back to
mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
and !CONFIG_MEMCG.

Before fix (swappiness=max ignored, mostly file pages reclaimed):

    # cat /proc/sys/vm/swappiness
    60
    # cat /proc/vmstat | grep pgsteal
    pgsteal_kswapd 0
    pgsteal_direct 0
    pgsteal_khugepaged 0
    pgsteal_proactive 1840
    pgsteal_anon 25
    pgsteal_file 1815
    # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
    # cat /proc/vmstat | grep pgsteal
    pgsteal_kswapd 0
    pgsteal_direct 0
    pgsteal_khugepaged 0
    pgsteal_proactive 18013
    pgsteal_anon 337
    pgsteal_file 17676

After fix (swappiness=max honored, anon pages reclaimed as expected):

    # cat /proc/vmstat | grep pgsteal
    pgsteal_kswapd 0
    pgsteal_direct 0
    pgsteal_khugepaged 0
    pgsteal_proactive 0
    pgsteal_anon 0
    pgsteal_file 0
    # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
    # cat /proc/vmstat | grep pgsteal
    pgsteal_kswapd 0
    pgsteal_direct 0
    pgsteal_khugepaged 0
    pgsteal_proactive 16283
    pgsteal_anon 16283
    pgsteal_file 0

Cc: stable@vger.kernel.org # 6.17+
Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface")
Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Barry Song <baohua@kernel.org>
---
 mm/vmscan.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 986dde8e7429..bd71595c8b2b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -199,6 +199,13 @@ struct scan_control {
  */
 int vm_swappiness = 60;
 
+static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
+{
+	if (sc->proactive && sc->proactive_swappiness)
+		return *sc->proactive_swappiness;
+	return mem_cgroup_swappiness(memcg);
+}
+
 #ifdef CONFIG_MEMCG
 
 /* Returns true for reclaim through cgroup limits or cgroup interfaces. */
@@ -239,13 +246,6 @@ static bool writeback_throttling_sane(struct scan_control *sc)
 #endif
 	return false;
 }
-
-static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
-{
-	if (sc->proactive && sc->proactive_swappiness)
-		return *sc->proactive_swappiness;
-	return mem_cgroup_swappiness(memcg);
-}
 #else
 static bool cgroup_reclaim(struct scan_control *sc)
 {
@@ -261,11 +261,6 @@ static bool writeback_throttling_sane(struct scan_control *sc)
 {
 	return true;
 }
-
-static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
-{
-	return READ_ONCE(vm_swappiness);
-}
 #endif
 
 static void set_task_reclaim_state(struct task_struct *task,
-- 
2.34.1

Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Qi Zheng]

On 7/16/26 11:17 AM, Ridong wrote:
> From: Ridong Chen <chenridong@xiaomi.com>
> 
> sc_swappiness() had two separate definitions depending on
> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
> vm_swappiness, ignoring the proactive_swappiness value passed
> through scan_control. This caused the swappiness parameter
> written to /sys/devices/system/node/nodeX/reclaim to have no
> effect when CONFIG_MEMCG is disabled.
> 
> Fix this by consolidating sc_swappiness() into a single definition
> that checks sc->proactive_swappiness first, then falls back to
> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
> and !CONFIG_MEMCG.
> 
> Before fix (swappiness=max ignored, mostly file pages reclaimed):
> 
>      # cat /proc/sys/vm/swappiness
>      60
>      # cat /proc/vmstat | grep pgsteal
>      pgsteal_kswapd 0
>      pgsteal_direct 0
>      pgsteal_khugepaged 0
>      pgsteal_proactive 1840
>      pgsteal_anon 25
>      pgsteal_file 1815
>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
>      # cat /proc/vmstat | grep pgsteal
>      pgsteal_kswapd 0
>      pgsteal_direct 0
>      pgsteal_khugepaged 0
>      pgsteal_proactive 18013
>      pgsteal_anon 337
>      pgsteal_file 17676
> 
> After fix (swappiness=max honored, anon pages reclaimed as expected):
> 
>      # cat /proc/vmstat | grep pgsteal
>      pgsteal_kswapd 0
>      pgsteal_direct 0
>      pgsteal_khugepaged 0
>      pgsteal_proactive 0
>      pgsteal_anon 0
>      pgsteal_file 0
>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
>      # cat /proc/vmstat | grep pgsteal
>      pgsteal_kswapd 0
>      pgsteal_direct 0
>      pgsteal_khugepaged 0
>      pgsteal_proactive 16283
>      pgsteal_anon 16283
>      pgsteal_file 0
> 
> Cc: stable@vger.kernel.org # 6.17+
> Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface")
> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Barry Song <baohua@kernel.org>
> ---
>   mm/vmscan.c | 19 +++++++------------
>   1 file changed, 7 insertions(+), 12 deletions(-)

Thanks for fixing this!

Acked-by: Qi Zheng <qi.zheng@linux.dev>

Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Qi Zheng]

Hi Ridong,

On 7/16/26 11:17 AM, Ridong wrote:
> From: Ridong Chen <chenridong@xiaomi.com>
> 
> sc_swappiness() had two separate definitions depending on
> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
> vm_swappiness, ignoring the proactive_swappiness value passed
> through scan_control. This caused the swappiness parameter
> written to /sys/devices/system/node/nodeX/reclaim to have no
> effect when CONFIG_MEMCG is disabled.
> 
> Fix this by consolidating sc_swappiness() into a single definition
> that checks sc->proactive_swappiness first, then falls back to
> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
> and !CONFIG_MEMCG.
> 
> Before fix (swappiness=max ignored, mostly file pages reclaimed):
> 
>      # cat /proc/sys/vm/swappiness
>      60
>      # cat /proc/vmstat | grep pgsteal
>      pgsteal_kswapd 0
>      pgsteal_direct 0
>      pgsteal_khugepaged 0
>      pgsteal_proactive 1840
>      pgsteal_anon 25
>      pgsteal_file 1815
>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
>      # cat /proc/vmstat | grep pgsteal
>      pgsteal_kswapd 0
>      pgsteal_direct 0
>      pgsteal_khugepaged 0
>      pgsteal_proactive 18013
>      pgsteal_anon 337
>      pgsteal_file 17676
> 
> After fix (swappiness=max honored, anon pages reclaimed as expected):
> 

By the way, in get_scan_count(), it seems we still reclaim file pages
without swap space, even if swappiness=max (SWAPPINESS_ANON_ONLY) is
set.

This behavior appears to contradict the semantics of
SWAPPINESS_ANON_ONLY, which probably needs a fix as well.

Thanks,
Qi

Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Tao Cui]

Hi Ridong,

Reproduced the bug and verified the fix in a QEMU x86_64 guest with
CONFIG_MEMCG disabled. Global vm.swappiness pinned to 1, then:

    echo "64M swappiness=<x>" > /sys/devices/system/node/node0/reclaim

  swappiness= | buggy (anon/file)   | patched (anon/file)
  ----------- | -------------------- | --------------------
  max         |      0  /  16385     |  16292  /  0
  200         |      2  /  16384     |  16837  /  0
  1           |      0  /  16386     |      0  /  16467

Unpatched ignores the swappiness arg (always file); patched honors it.
Matches the commit message.

Tested-by: Song Hu <husong@kylinos.cn>
Reviewed-by: Song Hu <husong@kylinos.cn>

在 2026/7/16 11:17, Ridong 写道:
> From: Ridong Chen <chenridong@xiaomi.com>
> 
> sc_swappiness() had two separate definitions depending on
> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
> vm_swappiness, ignoring the proactive_swappiness value passed
> through scan_control. This caused the swappiness parameter
> written to /sys/devices/system/node/nodeX/reclaim to have no
> effect when CONFIG_MEMCG is disabled.
> 
> Fix this by consolidating sc_swappiness() into a single definition
> that checks sc->proactive_swappiness first, then falls back to
> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
> and !CONFIG_MEMCG.
> 
> Before fix (swappiness=max ignored, mostly file pages reclaimed):
> 
>     # cat /proc/sys/vm/swappiness
>     60
>     # cat /proc/vmstat | grep pgsteal
>     pgsteal_kswapd 0
>     pgsteal_direct 0
>     pgsteal_khugepaged 0
>     pgsteal_proactive 1840
>     pgsteal_anon 25
>     pgsteal_file 1815
>     # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
>     # cat /proc/vmstat | grep pgsteal
>     pgsteal_kswapd 0
>     pgsteal_direct 0
>     pgsteal_khugepaged 0
>     pgsteal_proactive 18013
>     pgsteal_anon 337
>     pgsteal_file 17676
> 
> After fix (swappiness=max honored, anon pages reclaimed as expected):
> 
>     # cat /proc/vmstat | grep pgsteal
>     pgsteal_kswapd 0
>     pgsteal_direct 0
>     pgsteal_khugepaged 0
>     pgsteal_proactive 0
>     pgsteal_anon 0
>     pgsteal_file 0
>     # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
>     # cat /proc/vmstat | grep pgsteal
>     pgsteal_kswapd 0
>     pgsteal_direct 0
>     pgsteal_khugepaged 0
>     pgsteal_proactive 16283
>     pgsteal_anon 16283
>     pgsteal_file 0
> 
> Cc: stable@vger.kernel.org # 6.17+
> Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface")
> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Barry Song <baohua@kernel.org>
> ---
>  mm/vmscan.c | 19 +++++++------------
>  1 file changed, 7 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 986dde8e7429..bd71595c8b2b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -199,6 +199,13 @@ struct scan_control {
>   */
>  int vm_swappiness = 60;
>  
> +static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
> +{
> +	if (sc->proactive && sc->proactive_swappiness)
> +		return *sc->proactive_swappiness;
> +	return mem_cgroup_swappiness(memcg);
> +}
> +
>  #ifdef CONFIG_MEMCG
>  
>  /* Returns true for reclaim through cgroup limits or cgroup interfaces. */
> @@ -239,13 +246,6 @@ static bool writeback_throttling_sane(struct scan_control *sc)
>  #endif
>  	return false;
>  }
> -
> -static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
> -{
> -	if (sc->proactive && sc->proactive_swappiness)
> -		return *sc->proactive_swappiness;
> -	return mem_cgroup_swappiness(memcg);
> -}
>  #else
>  static bool cgroup_reclaim(struct scan_control *sc)
>  {
> @@ -261,11 +261,6 @@ static bool writeback_throttling_sane(struct scan_control *sc)
>  {
>  	return true;
>  }
> -
> -static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
> -{
> -	return READ_ONCE(vm_swappiness);
> -}
>  #endif
>  
>  static void set_task_reclaim_state(struct task_struct *task,

Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Ridong Chen]

On 7/16/2026 11:58 AM, Qi Zheng wrote:
> Hi Ridong,
> 
> On 7/16/26 11:17 AM, Ridong wrote:
>> From: Ridong Chen <chenridong@xiaomi.com>
>>
>> sc_swappiness() had two separate definitions depending on
>> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
>> vm_swappiness, ignoring the proactive_swappiness value passed
>> through scan_control. This caused the swappiness parameter
>> written to /sys/devices/system/node/nodeX/reclaim to have no
>> effect when CONFIG_MEMCG is disabled.
>>
>> Fix this by consolidating sc_swappiness() into a single definition
>> that checks sc->proactive_swappiness first, then falls back to
>> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
>> and !CONFIG_MEMCG.
>>
>> Before fix (swappiness=max ignored, mostly file pages reclaimed):
>>
>>      # cat /proc/sys/vm/swappiness
>>      60
>>      # cat /proc/vmstat | grep pgsteal
>>      pgsteal_kswapd 0
>>      pgsteal_direct 0
>>      pgsteal_khugepaged 0
>>      pgsteal_proactive 1840
>>      pgsteal_anon 25
>>      pgsteal_file 1815
>>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
>>      # cat /proc/vmstat | grep pgsteal
>>      pgsteal_kswapd 0
>>      pgsteal_direct 0
>>      pgsteal_khugepaged 0
>>      pgsteal_proactive 18013
>>      pgsteal_anon 337
>>      pgsteal_file 17676
>>
>> After fix (swappiness=max honored, anon pages reclaimed as expected):
>>
> 
> By the way, in get_scan_count(), it seems we still reclaim file pages
> without swap space, even if swappiness=max (SWAPPINESS_ANON_ONLY) is
> set.
> 
> This behavior appears to contradict the semantics of
> SWAPPINESS_ANON_ONLY, which probably needs a fix as well.
> 
Thanks, Qi.

You're right. Currently, when can_reclaim_anon_pages() returns false, 
the reclaim logic falls back to scanning file folios even if swappiness 
== SWAPPINESS_ANON_ONLY is set:

```
static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
			   unsigned long *nr)
{
	....
	/* If we have no swap space, do not bother scanning anon folios. */
	if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
		scan_balance = SCAN_FILE;
		goto out;
	}

	...
	/* Proactive reclaim initiated by userspace for anonymous memory only */
	if (swappiness == SWAPPINESS_ANON_ONLY) {
		WARN_ON_ONCE(!sc->proactive);
		scan_balance = SCAN_ANON;
		goto out;
	}
	...
}
```

The !can_reclaim_anon_pages() check above takes precedence over the 
SWAPPINESS_ANON_ONLY branch, making the latter effectively unreachable 
when anonymous pages are deemed non-reclaimable.

To fix this, could we move the SWAPPINESS_ANON_ONLY check up before the 
can_reclaim_anon_pages() check?

```
static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
			   unsigned long *nr)
{
	...
	/* Proactive reclaim initiated by userspace for anonymous memory only */
	if (swappiness == SWAPPINESS_ANON_ONLY) {
		WARN_ON_ONCE(!sc->proactive);
		scan_balance = SCAN_ANON;
		goto out;
	}
	....
	/* If we have no swap space, do not bother scanning anon folios. */
	if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
		scan_balance = SCAN_FILE;
		goto out;
	}

	...
}
```

-- 
Best regards
Ridong

Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Ridong Chen]

On 7/16/2026 2:06 PM, Tao Cui wrote:
> Hi Ridong,
> 
> Reproduced the bug and verified the fix in a QEMU x86_64 guest with
> CONFIG_MEMCG disabled. Global vm.swappiness pinned to 1, then:
> 
>      echo "64M swappiness=<x>" > /sys/devices/system/node/node0/reclaim
> 
>    swappiness= | buggy (anon/file)   | patched (anon/file)
>    ----------- | -------------------- | --------------------
>    max         |      0  /  16385     |  16292  /  0
>    200         |      2  /  16384     |  16837  /  0
>    1           |      0  /  16386     |      0  /  16467
> 
> Unpatched ignores the swappiness arg (always file); patched honors it.
> Matches the commit message.
> 
> Tested-by: Song Hu <husong@kylinos.cn>
> Reviewed-by: Song Hu <husong@kylinos.cn>
> 
Thanks.

-- 
Best regards
Ridong

Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Qi Zheng]

On 7/16/26 4:21 PM, Ridong Chen wrote:
> 
> 
> On 7/16/2026 11:58 AM, Qi Zheng wrote:
>> Hi Ridong,
>>
>> On 7/16/26 11:17 AM, Ridong wrote:
>>> From: Ridong Chen <chenridong@xiaomi.com>
>>>
>>> sc_swappiness() had two separate definitions depending on
>>> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
>>> vm_swappiness, ignoring the proactive_swappiness value passed
>>> through scan_control. This caused the swappiness parameter
>>> written to /sys/devices/system/node/nodeX/reclaim to have no
>>> effect when CONFIG_MEMCG is disabled.
>>>
>>> Fix this by consolidating sc_swappiness() into a single definition
>>> that checks sc->proactive_swappiness first, then falls back to
>>> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
>>> and !CONFIG_MEMCG.
>>>
>>> Before fix (swappiness=max ignored, mostly file pages reclaimed):
>>>
>>>      # cat /proc/sys/vm/swappiness
>>>      60
>>>      # cat /proc/vmstat | grep pgsteal
>>>      pgsteal_kswapd 0
>>>      pgsteal_direct 0
>>>      pgsteal_khugepaged 0
>>>      pgsteal_proactive 1840
>>>      pgsteal_anon 25
>>>      pgsteal_file 1815
>>>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/ 
>>> reclaim
>>>      # cat /proc/vmstat | grep pgsteal
>>>      pgsteal_kswapd 0
>>>      pgsteal_direct 0
>>>      pgsteal_khugepaged 0
>>>      pgsteal_proactive 18013
>>>      pgsteal_anon 337
>>>      pgsteal_file 17676
>>>
>>> After fix (swappiness=max honored, anon pages reclaimed as expected):
>>>
>>
>> By the way, in get_scan_count(), it seems we still reclaim file pages
>> without swap space, even if swappiness=max (SWAPPINESS_ANON_ONLY) is
>> set.
>>
>> This behavior appears to contradict the semantics of
>> SWAPPINESS_ANON_ONLY, which probably needs a fix as well.
>>
> Thanks, Qi.
> 
> You're right. Currently, when can_reclaim_anon_pages() returns false, 
> the reclaim logic falls back to scanning file folios even if swappiness 
> == SWAPPINESS_ANON_ONLY is set:
> 
> ```
> static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>                 unsigned long *nr)
> {
>      ....
>      /* If we have no swap space, do not bother scanning anon folios. */
>      if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, 
> sc)) {
>          scan_balance = SCAN_FILE;
>          goto out;
>      }
> 
>      ...
>      /* Proactive reclaim initiated by userspace for anonymous memory 
> only */
>      if (swappiness == SWAPPINESS_ANON_ONLY) {
>          WARN_ON_ONCE(!sc->proactive);
>          scan_balance = SCAN_ANON;
>          goto out;
>      }
>      ...
> }
> ```
> 
> The !can_reclaim_anon_pages() check above takes precedence over the 
> SWAPPINESS_ANON_ONLY branch, making the latter effectively unreachable 
> when anonymous pages are deemed non-reclaimable.
> 
> To fix this, could we move the SWAPPINESS_ANON_ONLY check up before the 
> can_reclaim_anon_pages() check?
> 
> ```
> static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>                 unsigned long *nr)
> {
>      ...
>      /* Proactive reclaim initiated by userspace for anonymous memory 
> only */
>      if (swappiness == SWAPPINESS_ANON_ONLY) {
>          WARN_ON_ONCE(!sc->proactive);
>          scan_balance = SCAN_ANON;
>          goto out;

For SWAPPINESS_ANON_ONLY + !can_reclaim_anon_pages, perhaps we should
just return directly instead of goto out, since no pages can be
reclaimed in this situation.

Thanks,
Qi

>      }
>      ....
>      /* If we have no swap space, do not bother scanning anon folios. */
>      if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, 
> sc)) {
>          scan_balance = SCAN_FILE;
>          goto out;
>      }
> 
>      ...
> }
> ```
> 

Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Ridong Chen]

On 7/16/2026 4:42 PM, Qi Zheng wrote:
> 
> 
> On 7/16/26 4:21 PM, Ridong Chen wrote:
>>
>>
>> On 7/16/2026 11:58 AM, Qi Zheng wrote:
>>> Hi Ridong,
>>>
>>> On 7/16/26 11:17 AM, Ridong wrote:
>>>> From: Ridong Chen <chenridong@xiaomi.com>
>>>>
>>>> sc_swappiness() had two separate definitions depending on
>>>> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
>>>> vm_swappiness, ignoring the proactive_swappiness value passed
>>>> through scan_control. This caused the swappiness parameter
>>>> written to /sys/devices/system/node/nodeX/reclaim to have no
>>>> effect when CONFIG_MEMCG is disabled.
>>>>
>>>> Fix this by consolidating sc_swappiness() into a single definition
>>>> that checks sc->proactive_swappiness first, then falls back to
>>>> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
>>>> and !CONFIG_MEMCG.
>>>>
>>>> Before fix (swappiness=max ignored, mostly file pages reclaimed):
>>>>
>>>>      # cat /proc/sys/vm/swappiness
>>>>      60
>>>>      # cat /proc/vmstat | grep pgsteal
>>>>      pgsteal_kswapd 0
>>>>      pgsteal_direct 0
>>>>      pgsteal_khugepaged 0
>>>>      pgsteal_proactive 1840
>>>>      pgsteal_anon 25
>>>>      pgsteal_file 1815
>>>>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/ 
>>>> reclaim
>>>>      # cat /proc/vmstat | grep pgsteal
>>>>      pgsteal_kswapd 0
>>>>      pgsteal_direct 0
>>>>      pgsteal_khugepaged 0
>>>>      pgsteal_proactive 18013
>>>>      pgsteal_anon 337
>>>>      pgsteal_file 17676
>>>>
>>>> After fix (swappiness=max honored, anon pages reclaimed as expected):
>>>>
>>>
>>> By the way, in get_scan_count(), it seems we still reclaim file pages
>>> without swap space, even if swappiness=max (SWAPPINESS_ANON_ONLY) is
>>> set.
>>>
>>> This behavior appears to contradict the semantics of
>>> SWAPPINESS_ANON_ONLY, which probably needs a fix as well.
>>>
>> Thanks, Qi.
>>
>> You're right. Currently, when can_reclaim_anon_pages() returns false, 
>> the reclaim logic falls back to scanning file folios even if 
>> swappiness == SWAPPINESS_ANON_ONLY is set:
>>
>> ```
>> static void get_scan_count(struct lruvec *lruvec, struct scan_control 
>> *sc,
>>                 unsigned long *nr)
>> {
>>      ....
>>      /* If we have no swap space, do not bother scanning anon folios. */
>>      if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat- 
>> >node_id, sc)) {
>>          scan_balance = SCAN_FILE;
>>          goto out;
>>      }
>>
>>      ...
>>      /* Proactive reclaim initiated by userspace for anonymous memory 
>> only */
>>      if (swappiness == SWAPPINESS_ANON_ONLY) {
>>          WARN_ON_ONCE(!sc->proactive);
>>          scan_balance = SCAN_ANON;
>>          goto out;
>>      }
>>      ...
>> }
>> ```
>>
>> The !can_reclaim_anon_pages() check above takes precedence over the 
>> SWAPPINESS_ANON_ONLY branch, making the latter effectively unreachable 
>> when anonymous pages are deemed non-reclaimable.
>>
>> To fix this, could we move the SWAPPINESS_ANON_ONLY check up before 
>> the can_reclaim_anon_pages() check?
>>
>> ```
>> static void get_scan_count(struct lruvec *lruvec, struct scan_control 
>> *sc,
>>                 unsigned long *nr)
>> {
>>      ...
>>      /* Proactive reclaim initiated by userspace for anonymous memory 
>> only */
>>      if (swappiness == SWAPPINESS_ANON_ONLY) {
>>          WARN_ON_ONCE(!sc->proactive);
>>          scan_balance = SCAN_ANON;
>>          goto out;
> 
> For SWAPPINESS_ANON_ONLY + !can_reclaim_anon_pages, perhaps we should
> just return directly instead of goto out, since no pages can be
> reclaimed in this situation.
> 

Much better.
Would you mind if I send a separate patch to fix this issue?

> 
>>      }
>>      ....
>>      /* If we have no swap space, do not bother scanning anon folios. */
>>      if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat- 
>> >node_id, sc)) {
>>          scan_balance = SCAN_FILE;
>>          goto out;
>>      }
>>
>>      ...
>> }
>> ```
>>
> 

-- 
Best regards
Ridong

Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Qi Zheng]

On 7/16/26 7:17 PM, Ridong Chen wrote:
> 
> 
> On 7/16/2026 4:42 PM, Qi Zheng wrote:
>>
>>
>> On 7/16/26 4:21 PM, Ridong Chen wrote:
>>>
>>>
>>> On 7/16/2026 11:58 AM, Qi Zheng wrote:
>>>> Hi Ridong,
>>>>
>>>> On 7/16/26 11:17 AM, Ridong wrote:
>>>>> From: Ridong Chen <chenridong@xiaomi.com>
>>>>>
>>>>> sc_swappiness() had two separate definitions depending on
>>>>> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
>>>>> vm_swappiness, ignoring the proactive_swappiness value passed
>>>>> through scan_control. This caused the swappiness parameter
>>>>> written to /sys/devices/system/node/nodeX/reclaim to have no
>>>>> effect when CONFIG_MEMCG is disabled.
>>>>>
>>>>> Fix this by consolidating sc_swappiness() into a single definition
>>>>> that checks sc->proactive_swappiness first, then falls back to
>>>>> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
>>>>> and !CONFIG_MEMCG.
>>>>>
>>>>> Before fix (swappiness=max ignored, mostly file pages reclaimed):
>>>>>
>>>>>      # cat /proc/sys/vm/swappiness
>>>>>      60
>>>>>      # cat /proc/vmstat | grep pgsteal
>>>>>      pgsteal_kswapd 0
>>>>>      pgsteal_direct 0
>>>>>      pgsteal_khugepaged 0
>>>>>      pgsteal_proactive 1840
>>>>>      pgsteal_anon 25
>>>>>      pgsteal_file 1815
>>>>>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/ 
>>>>> reclaim
>>>>>      # cat /proc/vmstat | grep pgsteal
>>>>>      pgsteal_kswapd 0
>>>>>      pgsteal_direct 0
>>>>>      pgsteal_khugepaged 0
>>>>>      pgsteal_proactive 18013
>>>>>      pgsteal_anon 337
>>>>>      pgsteal_file 17676
>>>>>
>>>>> After fix (swappiness=max honored, anon pages reclaimed as expected):
>>>>>
>>>>
>>>> By the way, in get_scan_count(), it seems we still reclaim file pages
>>>> without swap space, even if swappiness=max (SWAPPINESS_ANON_ONLY) is
>>>> set.
>>>>
>>>> This behavior appears to contradict the semantics of
>>>> SWAPPINESS_ANON_ONLY, which probably needs a fix as well.
>>>>
>>> Thanks, Qi.
>>>
>>> You're right. Currently, when can_reclaim_anon_pages() returns false, 
>>> the reclaim logic falls back to scanning file folios even if 
>>> swappiness == SWAPPINESS_ANON_ONLY is set:
>>>
>>> ```
>>> static void get_scan_count(struct lruvec *lruvec, struct scan_control 
>>> *sc,
>>>                 unsigned long *nr)
>>> {
>>>      ....
>>>      /* If we have no swap space, do not bother scanning anon folios. */
>>>      if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat- 
>>> >node_id, sc)) {
>>>          scan_balance = SCAN_FILE;
>>>          goto out;
>>>      }
>>>
>>>      ...
>>>      /* Proactive reclaim initiated by userspace for anonymous memory 
>>> only */
>>>      if (swappiness == SWAPPINESS_ANON_ONLY) {
>>>          WARN_ON_ONCE(!sc->proactive);
>>>          scan_balance = SCAN_ANON;
>>>          goto out;
>>>      }
>>>      ...
>>> }
>>> ```
>>>
>>> The !can_reclaim_anon_pages() check above takes precedence over the 
>>> SWAPPINESS_ANON_ONLY branch, making the latter effectively 
>>> unreachable when anonymous pages are deemed non-reclaimable.
>>>
>>> To fix this, could we move the SWAPPINESS_ANON_ONLY check up before 
>>> the can_reclaim_anon_pages() check?
>>>
>>> ```
>>> static void get_scan_count(struct lruvec *lruvec, struct scan_control 
>>> *sc,
>>>                 unsigned long *nr)
>>> {
>>>      ...
>>>      /* Proactive reclaim initiated by userspace for anonymous memory 
>>> only */
>>>      if (swappiness == SWAPPINESS_ANON_ONLY) {
>>>          WARN_ON_ONCE(!sc->proactive);
>>>          scan_balance = SCAN_ANON;
>>>          goto out;
>>
>> For SWAPPINESS_ANON_ONLY + !can_reclaim_anon_pages, perhaps we should
>> just return directly instead of goto out, since no pages can be
>> reclaimed in this situation.
>>
> 
> Much better.
> Would you mind if I send a separate patch to fix this issue?
>

Sure, thanks for your time on this, and I look forward to your fix!