[PATCH V1 0/1] sched/numa: Fix mm numa_scan_seq based unconditional scan

[PATCH V1 0/1] sched/numa: Fix mm numa_scan_seq based unconditional scan

[Raghavendra K T]

NUMA balancing code that updates PTEs by allowing unconditional scan
based on the value of processes' mm numa_scan_seq is not perfect.

More description is in patch1.

Have used the below patch to identify the corner case.

Detailed Result: (Only part of the result is updated
in patch1 to save space in commit log)

Detailed Result:

SUT: AMD EPYC Milan with 2 NUMA nodes 256 cpus.

Base kernel: upstream 6.6-rc6 (dd72f9c7e512) with Mels patch-series
from tip/sched/core [1] applied.

Summary: Some benchmarks imrove. There is increase in system
time due to additional scanning. But elapsed time shows gain.

However there is also some overhead seen for benchmarks like NUMA01.

kernbench
==========		base                  patched
Amean     user-128    13799.58 (   0.00%)    13789.86 *   0.07%*
Amean     syst-128     3280.80 (   0.00%)     3249.67 *   0.95%*
Amean     elsp-128      165.09 (   0.00%)      164.78 *   0.19%*

Duration User       41404.28    41375.08
Duration System      9862.22     9768.48
Duration Elapsed      519.87      518.72

Ops NUMA PTE updates                 1041416.00      831536.00
Ops NUMA hint faults                  263296.00      220966.00
Ops NUMA pages migrated               258021.00      212769.00
Ops AutoNUMA cost                       1328.67        1114.69

autonumabench

NUMA01_THREADLOCAL
==================
Amean     syst-NUMA01_THREADLOCAL       10.65 (   0.00%)       26.47 *-148.59%*
Amean     elsp-NUMA01_THREADLOCAL       81.79 (   0.00%)       67.74 *  17.18%*

Duration User       54832.73    47379.67
Duration System        75.00      185.75
Duration Elapsed      576.72      476.09

Ops NUMA PTE updates                  394429.00    11121044.00
Ops NUMA hint faults                    1001.00     8906404.00
Ops NUMA pages migrated                  288.00     2998694.00
Ops AutoNUMA cost                          7.77       44666.84

NUMA01
=====
Amean     syst-NUMA01       31.97 (   0.00%)       52.95 * -65.62%*
Amean     elsp-NUMA01      143.16 (   0.00%)      150.81 *  -5.34%*

Duration User       84839.49    91342.19
Duration System       224.26      371.12
Duration Elapsed     1005.64     1059.01

Ops NUMA PTE updates                33929508.00    50116313.00
Ops NUMA hint faults                34993820.00    52895783.00
Ops NUMA pages migrated              5456115.00     7441228.00
Ops AutoNUMA cost                     175310.27      264971.11

NUMA02
=========
Amean     syst-NUMA02        0.86 (   0.00%)        0.86 *  -0.50%*
Amean     elsp-NUMA02        3.99 (   0.00%)        3.82 *   4.40%*

Duration User        1186.06     1092.07
Duration System         6.44        6.47
Duration Elapsed       31.28       30.30

Ops NUMA PTE updates                     776.00         731.00
Ops NUMA hint faults                     527.00         490.00
Ops NUMA pages migrated                  183.00         153.00
Ops AutoNUMA cost                          2.64           2.46

Link: https://lore.kernel.org/linux-mm/ZSXF3AFZgIld1meX@gmail.com/T/

Raghavendra K T (1):
  sched/numa: Fix mm numa_scan_seq based unconditional scan

 include/linux/mm_types.h | 3 +++
 kernel/sched/fair.c      | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

---8<---
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 010ba1b7cb0e..a4870b01c8a1 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -10,6 +10,30 @@
 #include <linux/tracepoint.h>
 #include <linux/binfmts.h>
 
+TRACE_EVENT(sched_vma_start_seq,
+
+	TP_PROTO(struct task_struct *t, struct vm_area_struct *vma, int start_seq),
+
+	TP_ARGS(t, vma, start_seq),
+
+	TP_STRUCT__entry(
+		__array(	char,	comm,	TASK_COMM_LEN	)
+		__field(	pid_t,	pid			)
+		__field(	void *,	vma			)
+		__field(	int, start_seq		)
+	),
+
+	TP_fast_assign(
+		memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
+		__entry->pid	= t->pid;
+		__entry->vma	= vma;
+		__entry->start_seq	= start_seq;
+	),
+
+	TP_printk("comm=%s pid=%d vma = %px start_seq=%d", __entry->comm, __entry->pid, __entry->vma,
+			 __entry->start_seq)
+);
+
 /*
  * Tracepoint for calling kthread_stop, performed to end a kthread:
  */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c8af3a7ccba7..e0c16ea8470b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3335,6 +3335,7 @@ static void task_numa_work(struct callback_head *work)
 				continue;
 
 			vma->numab_state->start_scan_seq = mm->numa_scan_seq;
+			trace_sched_vma_start_seq(p, vma, mm->numa_scan_seq);
 
 			vma->numab_state->next_scan = now +
 				msecs_to_jiffies(sysctl_numa_balancing_scan_delay);


-- 
2.34.1

[PATCH V1 1/1] sched/numa: Fix mm numa_scan_seq based unconditional scan

[Raghavendra K T]

Since commit fc137c0ddab2 ("sched/numa: enhance vma scanning logic")

NUMA Balancing allows updating PTEs to trap NUMA hinting faults if the
task had previously accessed VMA. However unconditional scan of VMAs are
allowed during initial phase of VMA creation until process's
mm numa_scan_seq reaches 2 even though current task had not accessed VMA.

Rationale:
 - Without initial scan subsequent PTE update may never happen.
 - Give fair opportunity to all the VMAs to be scanned and subsequently
understand the access pattern of all the VMAs.

But it has a corner case where, if a VMA is created after some time,
process's mm numa_scan_seq could be already greater than 2.

For e.g., values of mm numa_scan_seq when VMAs are created by running
mmtest autonuma benchmark briefly looks like:
start_seq=0 : 459
start_seq=2 : 138
start_seq=3 : 144
start_seq=4 : 8
start_seq=8 : 1
start_seq=9 : 1
This results in no unconditional PTE updates for those VMAs created after
some time.

Fix:
- Note down the initial value of mm numa_scan_seq in per VMA start_seq.
- Allow unconditional scan till start_seq + 2.

Result:
SUT: AMD EPYC Milan with 2 NUMA nodes 256 cpus.
base kernel: upstream 6.6-rc6 with Mels patches [1] applied.

kernbench
==========		base                  patched %gain
Amean    elsp-128      165.09 ( 0.00%)      164.78 *   0.19%*

Duration User       41404.28    41375.08
Duration System      9862.22     9768.48
Duration Elapsed      519.87      518.72

Ops NUMA PTE updates           1041416.00      831536.00
Ops NUMA hint faults            263296.00      220966.00
Ops NUMA pages migrated         258021.00      212769.00
Ops AutoNUMA cost                 1328.67        1114.69

autonumabench

NUMA01_THREADLOCAL
==================
Amean  elsp-NUMA01_THREADLOCAL   81.79 (0.00%)  67.74 *  17.18%*

Duration User       54832.73    47379.67
Duration System        75.00      185.75
Duration Elapsed      576.72      476.09

Ops NUMA PTE updates                  394429.00    11121044.00
Ops NUMA hint faults                    1001.00     8906404.00
Ops NUMA pages migrated                  288.00     2998694.00
Ops AutoNUMA cost                          7.77       44666.84

Link: https://lore.kernel.org/linux-mm/ZSXF3AFZgIld1meX@gmail.com/T/

Signed-off-by: Raghavendra K T <raghavendra.kt@amd.com>
---
 include/linux/mm_types.h | 3 +++
 kernel/sched/fair.c      | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 589f31ef2e84..679f076e3a91 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -576,6 +576,9 @@ struct vma_numab_state {
 	 */
 	unsigned long pids_active[2];
 
+	/* MM scan sequence ID when scan first started after VMA creation */
+	int start_scan_seq;
+
 	/*
 	 * MM scan sequence ID when the VMA was last completely scanned.
 	 * A VMA is not eligible for scanning if prev_scan_seq == numa_scan_seq
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5e03ced2b566..c8af3a7ccba7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3191,7 +3191,7 @@ static bool vma_is_accessed(struct mm_struct *mm, struct vm_area_struct *vma)
 	 * This is also done to avoid any side effect of task scanning
 	 * amplifying the unfairness of disjoint set of VMAs' access.
 	 */
-	if (READ_ONCE(current->mm->numa_scan_seq) < 2)
+	if ((READ_ONCE(current->mm->numa_scan_seq) - vma->numab_state->start_scan_seq) < 2)
 		return true;
 
 	pids = vma->numab_state->pids_active[0] | vma->numab_state->pids_active[1];
@@ -3334,6 +3334,8 @@ static void task_numa_work(struct callback_head *work)
 			if (!vma->numab_state)
 				continue;
 
+			vma->numab_state->start_scan_seq = mm->numa_scan_seq;
+
 			vma->numab_state->next_scan = now +
 				msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
 
-- 
2.34.1

Re: [PATCH V1 0/1] sched/numa: Fix mm numa_scan_seq based unconditional scan

[Raghavendra K T]

On 10/20/2023 9:27 PM, Raghavendra K T wrote:
> NUMA balancing code that updates PTEs by allowing unconditional scan
> based on the value of processes' mm numa_scan_seq is not perfect.
> 
> More description is in patch1.
> 
> Have used the below patch to identify the corner case.
> 
> Detailed Result: (Only part of the result is updated
> in patch1 to save space in commit log)
> 
> Detailed Result:
> 
> SUT: AMD EPYC Milan with 2 NUMA nodes 256 cpus.
> 
> Base kernel: upstream 6.6-rc6 (dd72f9c7e512) with Mels patch-series
> from tip/sched/core [1] applied.
> 
> Summary: Some benchmarks imrove. There is increase in system
> time due to additional scanning. But elapsed time shows gain.
> 
> However there is also some overhead seen for benchmarks like NUMA01.
> 
> kernbench
> ==========		base                  patched
> Amean     user-128    13799.58 (   0.00%)    13789.86 *   0.07%*
> Amean     syst-128     3280.80 (   0.00%)     3249.67 *   0.95%*
> Amean     elsp-128      165.09 (   0.00%)      164.78 *   0.19%*
> 
> Duration User       41404.28    41375.08
> Duration System      9862.22     9768.48
> Duration Elapsed      519.87      518.72
> 
> Ops NUMA PTE updates                 1041416.00      831536.00
> Ops NUMA hint faults                  263296.00      220966.00
> Ops NUMA pages migrated               258021.00      212769.00
> Ops AutoNUMA cost                       1328.67        1114.69
> 
> autonumabench
> 
> NUMA01_THREADLOCAL
> ==================
> Amean     syst-NUMA01_THREADLOCAL       10.65 (   0.00%)       26.47 *-148.59%*
> Amean     elsp-NUMA01_THREADLOCAL       81.79 (   0.00%)       67.74 *  17.18%*
> 
> Duration User       54832.73    47379.67
> Duration System        75.00      185.75
> Duration Elapsed      576.72      476.09
> 
> Ops NUMA PTE updates                  394429.00    11121044.00
> Ops NUMA hint faults                    1001.00     8906404.00
> Ops NUMA pages migrated                  288.00     2998694.00
> Ops AutoNUMA cost                          7.77       44666.84
> 
> NUMA01
> =====
> Amean     syst-NUMA01       31.97 (   0.00%)       52.95 * -65.62%*
> Amean     elsp-NUMA01      143.16 (   0.00%)      150.81 *  -5.34%*
> 
> Duration User       84839.49    91342.19
> Duration System       224.26      371.12
> Duration Elapsed     1005.64     1059.01
> 
> Ops NUMA PTE updates                33929508.00    50116313.00
> Ops NUMA hint faults                34993820.00    52895783.00
> Ops NUMA pages migrated              5456115.00     7441228.00
> Ops AutoNUMA cost                     175310.27      264971.11
> 
> NUMA02
> =========
> Amean     syst-NUMA02        0.86 (   0.00%)        0.86 *  -0.50%*
> Amean     elsp-NUMA02        3.99 (   0.00%)        3.82 *   4.40%*
> 
> Duration User        1186.06     1092.07
> Duration System         6.44        6.47
> Duration Elapsed       31.28       30.30
> 
> Ops NUMA PTE updates                     776.00         731.00
> Ops NUMA hint faults                     527.00         490.00
> Ops NUMA pages migrated                  183.00         153.00
> Ops AutoNUMA cost                          2.64           2.46
> 
> Link: https://lore.kernel.org/linux-mm/ZSXF3AFZgIld1meX@gmail.com/T/
> 

Forgot to add skip_vma_count trace results:

autonumabench: numa01_THREAD_LOCAL 3 iterations

base:
inaccessible:13133
pid_inactive:15807
scan_delay:471
seq_completed:50
shared_ro:6983
unsuitable:3917

patched:
inaccessible:4727
pid_inactive:5119
scan_delay:455
seq_completed:7
shared_ro:2551
unsuitable:5402



> Raghavendra K T (1):
>    sched/numa: Fix mm numa_scan_seq based unconditional scan
> 
>   include/linux/mm_types.h | 3 +++
>   kernel/sched/fair.c      | 4 +++-
>   2 files changed, 6 insertions(+), 1 deletion(-)
> 
> ---8<---
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index 010ba1b7cb0e..a4870b01c8a1 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -10,6 +10,30 @@
>   #include <linux/tracepoint.h>
>   #include <linux/binfmts.h>
>   
> +TRACE_EVENT(sched_vma_start_seq,
> +
> +	TP_PROTO(struct task_struct *t, struct vm_area_struct *vma, int start_seq),
> +
> +	TP_ARGS(t, vma, start_seq),
> +
> +	TP_STRUCT__entry(
> +		__array(	char,	comm,	TASK_COMM_LEN	)
> +		__field(	pid_t,	pid			)
> +		__field(	void *,	vma			)
> +		__field(	int, start_seq		)
> +	),
> +
> +	TP_fast_assign(
> +		memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
> +		__entry->pid	= t->pid;
> +		__entry->vma	= vma;
> +		__entry->start_seq	= start_seq;
> +	),
> +
> +	TP_printk("comm=%s pid=%d vma = %px start_seq=%d", __entry->comm, __entry->pid, __entry->vma,
> +			 __entry->start_seq)
> +);
> +
>   /*
>    * Tracepoint for calling kthread_stop, performed to end a kthread:
>    */
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c8af3a7ccba7..e0c16ea8470b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3335,6 +3335,7 @@ static void task_numa_work(struct callback_head *work)
>   				continue;
>   
>   			vma->numab_state->start_scan_seq = mm->numa_scan_seq;
> +			trace_sched_vma_start_seq(p, vma, mm->numa_scan_seq);
>   
>   			vma->numab_state->next_scan = now +
>   				msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
> 
> 

Re: [PATCH V1 0/1] sched/numa: Fix mm numa_scan_seq based unconditional scan

[Raghavendra K T]

On 10/20/2023 9:27 PM, Raghavendra K T wrote:
> NUMA balancing code that updates PTEs by allowing unconditional scan
> based on the value of processes' mm numa_scan_seq is not perfect.
> 
> More description is in patch1.
> 
> Have used the below patch to identify the corner case.
> 
> Detailed Result: (Only part of the result is updated
> in patch1 to save space in commit log)
> 

Gentle ping to check if there are any concerns / comments
on the patch :)

Thanks and Regards
- Raghu

Re: [PATCH V1 1/1] sched/numa: Fix mm numa_scan_seq based unconditional scan

[Mel Gorman]

On Fri, Oct 20, 2023 at 09:27:46PM +0530, Raghavendra K T wrote:
> Since commit fc137c0ddab2 ("sched/numa: enhance vma scanning logic")
> 
> NUMA Balancing allows updating PTEs to trap NUMA hinting faults if the
> task had previously accessed VMA. However unconditional scan of VMAs are
> allowed during initial phase of VMA creation until process's
> mm numa_scan_seq reaches 2 even though current task had not accessed VMA.
> 
> Rationale:
>  - Without initial scan subsequent PTE update may never happen.
>  - Give fair opportunity to all the VMAs to be scanned and subsequently
> understand the access pattern of all the VMAs.
> 
> But it has a corner case where, if a VMA is created after some time,
> process's mm numa_scan_seq could be already greater than 2.
> 
> For e.g., values of mm numa_scan_seq when VMAs are created by running
> mmtest autonuma benchmark briefly looks like:
> start_seq=0 : 459
> start_seq=2 : 138
> start_seq=3 : 144
> start_seq=4 : 8
> start_seq=8 : 1
> start_seq=9 : 1
> This results in no unconditional PTE updates for those VMAs created after
> some time.
> 
> Fix:
> - Note down the initial value of mm numa_scan_seq in per VMA start_seq.
> - Allow unconditional scan till start_seq + 2.
> 
> Result:
> SUT: AMD EPYC Milan with 2 NUMA nodes 256 cpus.
> base kernel: upstream 6.6-rc6 with Mels patches [1] applied.
> 
> kernbench
> ==========		base                  patched %gain
> Amean    elsp-128      165.09 ( 0.00%)      164.78 *   0.19%*
> 
> Duration User       41404.28    41375.08
> Duration System      9862.22     9768.48
> Duration Elapsed      519.87      518.72
> 
> Ops NUMA PTE updates           1041416.00      831536.00
> Ops NUMA hint faults            263296.00      220966.00
> Ops NUMA pages migrated         258021.00      212769.00
> Ops AutoNUMA cost                 1328.67        1114.69
> 
> autonumabench
> 
> NUMA01_THREADLOCAL
> ==================
> Amean  elsp-NUMA01_THREADLOCAL   81.79 (0.00%)  67.74 *  17.18%*
> 
> Duration User       54832.73    47379.67
> Duration System        75.00      185.75
> Duration Elapsed      576.72      476.09
> 
> Ops NUMA PTE updates                  394429.00    11121044.00
> Ops NUMA hint faults                    1001.00     8906404.00
> Ops NUMA pages migrated                  288.00     2998694.00
> Ops AutoNUMA cost                          7.77       44666.84
> 
> Link: https://lore.kernel.org/linux-mm/ZSXF3AFZgIld1meX@gmail.com/T/
> 
> Signed-off-by: Raghavendra K T <raghavendra.kt@amd.com>

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

Re: [PATCH V1 1/1] sched/numa: Fix mm numa_scan_seq based unconditional scan

[Peter Zijlstra]

On Wed, Nov 01, 2023 at 09:21:01AM +0000, Mel Gorman wrote:
> On Fri, Oct 20, 2023 at 09:27:46PM +0530, Raghavendra K T wrote:
> > Since commit fc137c0ddab2 ("sched/numa: enhance vma scanning logic")
> > 
> > NUMA Balancing allows updating PTEs to trap NUMA hinting faults if the
> > task had previously accessed VMA. However unconditional scan of VMAs are
> > allowed during initial phase of VMA creation until process's
> > mm numa_scan_seq reaches 2 even though current task had not accessed VMA.
> > 
> > Rationale:
> >  - Without initial scan subsequent PTE update may never happen.
> >  - Give fair opportunity to all the VMAs to be scanned and subsequently
> > understand the access pattern of all the VMAs.
> > 
> > But it has a corner case where, if a VMA is created after some time,
> > process's mm numa_scan_seq could be already greater than 2.
> > 
> > For e.g., values of mm numa_scan_seq when VMAs are created by running
> > mmtest autonuma benchmark briefly looks like:
> > start_seq=0 : 459
> > start_seq=2 : 138
> > start_seq=3 : 144
> > start_seq=4 : 8
> > start_seq=8 : 1
> > start_seq=9 : 1
> > This results in no unconditional PTE updates for those VMAs created after
> > some time.
> > 
> > Fix:
> > - Note down the initial value of mm numa_scan_seq in per VMA start_seq.
> > - Allow unconditional scan till start_seq + 2.
> > 
> > Result:
> > SUT: AMD EPYC Milan with 2 NUMA nodes 256 cpus.
> > base kernel: upstream 6.6-rc6 with Mels patches [1] applied.
> > 
> > kernbench
> > ==========		base                  patched %gain
> > Amean    elsp-128      165.09 ( 0.00%)      164.78 *   0.19%*
> > 
> > Duration User       41404.28    41375.08
> > Duration System      9862.22     9768.48
> > Duration Elapsed      519.87      518.72
> > 
> > Ops NUMA PTE updates           1041416.00      831536.00
> > Ops NUMA hint faults            263296.00      220966.00
> > Ops NUMA pages migrated         258021.00      212769.00
> > Ops AutoNUMA cost                 1328.67        1114.69
> > 
> > autonumabench
> > 
> > NUMA01_THREADLOCAL
> > ==================
> > Amean  elsp-NUMA01_THREADLOCAL   81.79 (0.00%)  67.74 *  17.18%*
> > 
> > Duration User       54832.73    47379.67
> > Duration System        75.00      185.75
> > Duration Elapsed      576.72      476.09
> > 
> > Ops NUMA PTE updates                  394429.00    11121044.00
> > Ops NUMA hint faults                    1001.00     8906404.00
> > Ops NUMA pages migrated                  288.00     2998694.00
> > Ops AutoNUMA cost                          7.77       44666.84
> > 
> > Link: https://lore.kernel.org/linux-mm/ZSXF3AFZgIld1meX@gmail.com/T/
> > 
> > Signed-off-by: Raghavendra K T <raghavendra.kt@amd.com>
> 
> Acked-by: Mel Gorman <mgorman@suse.de>

Thanks, will queue for the next merge window (6.8 I think that is) once
6.7-rc1 comes around.

Re: [PATCH V1 1/1] sched/numa: Fix mm numa_scan_seq based unconditional scan

[Raghavendra K T]

On 11/1/2023 4:01 PM, Peter Zijlstra wrote:
> On Wed, Nov 01, 2023 at 09:21:01AM +0000, Mel Gorman wrote:
>> On Fri, Oct 20, 2023 at 09:27:46PM +0530, Raghavendra K T wrote:
>>> Since commit fc137c0ddab2 ("sched/numa: enhance vma scanning logic")
>>>
>>> NUMA Balancing allows updating PTEs to trap NUMA hinting faults if the
>>> task had previously accessed VMA. However unconditional scan of VMAs are
>>> allowed during initial phase of VMA creation until process's
>>> mm numa_scan_seq reaches 2 even though current task had not accessed VMA.
>>>
>>> Rationale:
>>>   - Without initial scan subsequent PTE update may never happen.
>>>   - Give fair opportunity to all the VMAs to be scanned and subsequently
>>> understand the access pattern of all the VMAs.
>>>
>>> But it has a corner case where, if a VMA is created after some time,
>>> process's mm numa_scan_seq could be already greater than 2.
>>>
>>> For e.g., values of mm numa_scan_seq when VMAs are created by running
>>> mmtest autonuma benchmark briefly looks like:
>>> start_seq=0 : 459
>>> start_seq=2 : 138
>>> start_seq=3 : 144
>>> start_seq=4 : 8
>>> start_seq=8 : 1
>>> start_seq=9 : 1
>>> This results in no unconditional PTE updates for those VMAs created after
>>> some time.
>>>
>>> Fix:
>>> - Note down the initial value of mm numa_scan_seq in per VMA start_seq.
>>> - Allow unconditional scan till start_seq + 2.
>>>
>>> Result:
>>> SUT: AMD EPYC Milan with 2 NUMA nodes 256 cpus.
>>> base kernel: upstream 6.6-rc6 with Mels patches [1] applied.
>>>
>>> kernbench
>>> ==========		base                  patched %gain
>>> Amean    elsp-128      165.09 ( 0.00%)      164.78 *   0.19%*
>>>
>>> Duration User       41404.28    41375.08
>>> Duration System      9862.22     9768.48
>>> Duration Elapsed      519.87      518.72
>>>
>>> Ops NUMA PTE updates           1041416.00      831536.00
>>> Ops NUMA hint faults            263296.00      220966.00
>>> Ops NUMA pages migrated         258021.00      212769.00
>>> Ops AutoNUMA cost                 1328.67        1114.69
>>>
>>> autonumabench
>>>
>>> NUMA01_THREADLOCAL
>>> ==================
>>> Amean  elsp-NUMA01_THREADLOCAL   81.79 (0.00%)  67.74 *  17.18%*
>>>
>>> Duration User       54832.73    47379.67
>>> Duration System        75.00      185.75
>>> Duration Elapsed      576.72      476.09
>>>
>>> Ops NUMA PTE updates                  394429.00    11121044.00
>>> Ops NUMA hint faults                    1001.00     8906404.00
>>> Ops NUMA pages migrated                  288.00     2998694.00
>>> Ops AutoNUMA cost                          7.77       44666.84
>>>
>>> Link: https://lore.kernel.org/linux-mm/ZSXF3AFZgIld1meX@gmail.com/T/
>>>
>>> Signed-off-by: Raghavendra K T <raghavendra.kt@amd.com>
>>
>> Acked-by: Mel Gorman <mgorman@suse.de>
> 
> Thanks, will queue for the next merge window (6.8 I think that is) once
> 6.7-rc1 comes around.

Thank you Mel, PeterZ.

Meanwhile, I will check if extending #history (PeterZ) on this changed
baseline,  as well as implications of extending #bits for PIDS (Ingo) 
suggested (especially larger machine) helps and come back if I find
anything interesting.

Thanks and Regards
- Raghu