* [PATCH v2] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting
[not found] <20250729035101.1601407-1-ruansy.fnst@fujitsu.com>
@ 2025-09-01 2:05 ` Ruan Shiyang
2025-09-01 8:04 ` Vlastimil Babka
2025-09-01 9:01 ` [PATCH v3] " Ruan Shiyang
1 sibling, 1 reply; 7+ messages in thread
From: Ruan Shiyang @ 2025-09-01 2:05 UTC (permalink / raw)
To: linux-mm
Cc: linux-kernel, lkp, ying.huang, akpm, y-goto, mingo, peterz,
juri.lelli, vincent.guittot, dietmar.eggemann, rostedt, mgorman,
vschneid, Li Zhijian, Vlastimil Babka, Ben Segall, stable
Goto-san reported confusing pgpromote statistics where the
pgpromote_success count significantly exceeded pgpromote_candidate.
On a system with three nodes (nodes 0-1: DRAM 4GB, node 2: NVDIMM 4GB):
# Enable demotion only
echo 1 > /sys/kernel/mm/numa/demotion_enabled
numactl -m 0-1 memhog -r200 3500M >/dev/null &
pid=$!
sleep 2
numactl memhog -r100 2500M >/dev/null &
sleep 10
kill -9 $pid # terminate the 1st memhog
# Enable promotion
echo 2 > /proc/sys/kernel/numa_balancing
After a few seconds, we observeed `pgpromote_candidate < pgpromote_success`
$ grep -e pgpromote /proc/vmstat
pgpromote_success 2579
pgpromote_candidate 0
In this scenario, after terminating the first memhog, the conditions for
pgdat_free_space_enough() are quickly met, and triggers promotion.
However, these migrated pages are only counted for in PGPROMOTE_SUCCESS,
not in PGPROMOTE_CANDIDATE.
To solve these confusing statistics, introduce PGPROMOTE_CANDIDATE_NRL to
count the missed promotion pages. And also, not counting these pages into
PGPROMOTE_CANDIDATE is to avoid changing the existing algorithm or
performance of the promotion rate limit.
Link: https://lkml.kernel.org/r/20250729035101.1601407-1-ruansy.fnst@fujitsu.com
Co-developed-by: Li Zhijian <lizhijian@fujitsu.com>
Signed-off-by: Ruan Shiyang <ruansy.fnst@fujitsu.com>
Reported-by: Yasunori Gotou (Fujitsu) <y-goto@fujitsu.com>
Suggested-by: Huang Ying <ying.huang@linux.alibaba.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
Changes since v1:
1. change Li Zhijian from 'Signed-off-by' to 'Co-developed-by' per Vlastimil.
2. add Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
include/linux/mmzone.h | 16 +++++++++++++++-
kernel/sched/fair.c | 5 +++--
mm/vmstat.c | 1 +
3 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0c5da9141983..9d3ea9085556 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -234,7 +234,21 @@ enum node_stat_item {
#endif
#ifdef CONFIG_NUMA_BALANCING
PGPROMOTE_SUCCESS, /* promote successfully */
- PGPROMOTE_CANDIDATE, /* candidate pages to promote */
+ /**
+ * Candidate pages for promotion based on hint fault latency. This
+ * counter is used to control the promotion rate and adjust the hot
+ * threshold.
+ */
+ PGPROMOTE_CANDIDATE,
+ /**
+ * Not rate-limited (NRL) candidate pages for those can be promoted
+ * without considering hot threshold because of enough free pages in
+ * fast-tier node. These promotions bypass the regular hotness checks
+ * and do NOT influence the promotion rate-limiter or
+ * threshold-adjustment logic.
+ * This is for statistics/monitoring purposes.
+ */
+ PGPROMOTE_CANDIDATE_NRL,
#endif
/* PGDEMOTE_*: pages demoted */
PGDEMOTE_KSWAPD,
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b173a059315c..82c8d804c54c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1923,11 +1923,13 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
struct pglist_data *pgdat;
unsigned long rate_limit;
unsigned int latency, th, def_th;
+ long nr = folio_nr_pages(folio);
pgdat = NODE_DATA(dst_nid);
if (pgdat_free_space_enough(pgdat)) {
/* workload changed, reset hot threshold */
pgdat->nbp_threshold = 0;
+ mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE_NRL, nr);
return true;
}
@@ -1941,8 +1943,7 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
if (latency >= th)
return false;
- return !numa_promotion_rate_limit(pgdat, rate_limit,
- folio_nr_pages(folio));
+ return !numa_promotion_rate_limit(pgdat, rate_limit, nr);
}
this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 71cd1ceba191..e74f0b2a1021 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1280,6 +1280,7 @@ const char * const vmstat_text[] = {
#ifdef CONFIG_NUMA_BALANCING
[I(PGPROMOTE_SUCCESS)] = "pgpromote_success",
[I(PGPROMOTE_CANDIDATE)] = "pgpromote_candidate",
+ [I(PGPROMOTE_CANDIDATE_NRL)] = "pgpromote_candidate_nrl",
#endif
[I(PGDEMOTE_KSWAPD)] = "pgdemote_kswapd",
[I(PGDEMOTE_DIRECT)] = "pgdemote_direct",
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v2] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting
2025-09-01 2:05 ` [PATCH v2] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting Ruan Shiyang
@ 2025-09-01 8:04 ` Vlastimil Babka
0 siblings, 0 replies; 7+ messages in thread
From: Vlastimil Babka @ 2025-09-01 8:04 UTC (permalink / raw)
To: Ruan Shiyang, linux-mm
Cc: linux-kernel, lkp, ying.huang, akpm, y-goto, mingo, peterz,
juri.lelli, vincent.guittot, dietmar.eggemann, rostedt, mgorman,
vschneid, Li Zhijian, Ben Segall, stable
On 9/1/25 04:05, Ruan Shiyang wrote:
> Goto-san reported confusing pgpromote statistics where the
> pgpromote_success count significantly exceeded pgpromote_candidate.
>
> On a system with three nodes (nodes 0-1: DRAM 4GB, node 2: NVDIMM 4GB):
> # Enable demotion only
> echo 1 > /sys/kernel/mm/numa/demotion_enabled
> numactl -m 0-1 memhog -r200 3500M >/dev/null &
> pid=$!
> sleep 2
> numactl memhog -r100 2500M >/dev/null &
> sleep 10
> kill -9 $pid # terminate the 1st memhog
> # Enable promotion
> echo 2 > /proc/sys/kernel/numa_balancing
>
> After a few seconds, we observeed `pgpromote_candidate < pgpromote_success`
> $ grep -e pgpromote /proc/vmstat
> pgpromote_success 2579
> pgpromote_candidate 0
>
> In this scenario, after terminating the first memhog, the conditions for
> pgdat_free_space_enough() are quickly met, and triggers promotion.
> However, these migrated pages are only counted for in PGPROMOTE_SUCCESS,
> not in PGPROMOTE_CANDIDATE.
>
> To solve these confusing statistics, introduce PGPROMOTE_CANDIDATE_NRL to
> count the missed promotion pages. And also, not counting these pages into
> PGPROMOTE_CANDIDATE is to avoid changing the existing algorithm or
> performance of the promotion rate limit.
>
> Link: https://lkml.kernel.org/r/20250729035101.1601407-1-ruansy.fnst@fujitsu.com
> Co-developed-by: Li Zhijian <lizhijian@fujitsu.com>
> Signed-off-by: Ruan Shiyang <ruansy.fnst@fujitsu.com>
> Reported-by: Yasunori Gotou (Fujitsu) <y-goto@fujitsu.com>
> Suggested-by: Huang Ying <ying.huang@linux.alibaba.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> Changes since v1:
> 1. change Li Zhijian from 'Signed-off-by' to 'Co-developed-by' per Vlastimil.
Note according to the docs it should be both, Co-developed-by followed by
Signed-off-by.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v3] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting
[not found] <20250729035101.1601407-1-ruansy.fnst@fujitsu.com>
2025-09-01 2:05 ` [PATCH v2] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting Ruan Shiyang
@ 2025-09-01 9:01 ` Ruan Shiyang
2025-09-01 11:09 ` Huang, Ying
2025-09-01 19:59 ` Andrew Morton
1 sibling, 2 replies; 7+ messages in thread
From: Ruan Shiyang @ 2025-09-01 9:01 UTC (permalink / raw)
To: linux-mm
Cc: linux-kernel, lkp, ying.huang, akpm, y-goto, mingo, peterz,
juri.lelli, vincent.guittot, dietmar.eggemann, rostedt, mgorman,
vschneid, Li Zhijian, Vlastimil Babka, Ben Segall, stable
Goto-san reported confusing pgpromote statistics where the
pgpromote_success count significantly exceeded pgpromote_candidate.
On a system with three nodes (nodes 0-1: DRAM 4GB, node 2: NVDIMM 4GB):
# Enable demotion only
echo 1 > /sys/kernel/mm/numa/demotion_enabled
numactl -m 0-1 memhog -r200 3500M >/dev/null &
pid=$!
sleep 2
numactl memhog -r100 2500M >/dev/null &
sleep 10
kill -9 $pid # terminate the 1st memhog
# Enable promotion
echo 2 > /proc/sys/kernel/numa_balancing
After a few seconds, we observeed `pgpromote_candidate < pgpromote_success`
$ grep -e pgpromote /proc/vmstat
pgpromote_success 2579
pgpromote_candidate 0
In this scenario, after terminating the first memhog, the conditions for
pgdat_free_space_enough() are quickly met, and triggers promotion.
However, these migrated pages are only counted for in PGPROMOTE_SUCCESS,
not in PGPROMOTE_CANDIDATE.
To solve these confusing statistics, introduce PGPROMOTE_CANDIDATE_NRL to
count the missed promotion pages. And also, not counting these pages into
PGPROMOTE_CANDIDATE is to avoid changing the existing algorithm or
performance of the promotion rate limit.
Link: https://lkml.kernel.org/r/20250729035101.1601407-1-ruansy.fnst@fujitsu.com
Co-developed-by: Li Zhijian <lizhijian@fujitsu.com>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Signed-off-by: Ruan Shiyang <ruansy.fnst@fujitsu.com>
Reported-by: Yasunori Gotou (Fujitsu) <y-goto@fujitsu.com>
Suggested-by: Huang Ying <ying.huang@linux.alibaba.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
Changes since v2:
1. add 'Co-developed-by: Li Zhijian' followed by 'Signed-off-by' per Vlastimil.
---
include/linux/mmzone.h | 16 +++++++++++++++-
kernel/sched/fair.c | 5 +++--
mm/vmstat.c | 1 +
3 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0c5da9141983..9d3ea9085556 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -234,7 +234,21 @@ enum node_stat_item {
#endif
#ifdef CONFIG_NUMA_BALANCING
PGPROMOTE_SUCCESS, /* promote successfully */
- PGPROMOTE_CANDIDATE, /* candidate pages to promote */
+ /**
+ * Candidate pages for promotion based on hint fault latency. This
+ * counter is used to control the promotion rate and adjust the hot
+ * threshold.
+ */
+ PGPROMOTE_CANDIDATE,
+ /**
+ * Not rate-limited (NRL) candidate pages for those can be promoted
+ * without considering hot threshold because of enough free pages in
+ * fast-tier node. These promotions bypass the regular hotness checks
+ * and do NOT influence the promotion rate-limiter or
+ * threshold-adjustment logic.
+ * This is for statistics/monitoring purposes.
+ */
+ PGPROMOTE_CANDIDATE_NRL,
#endif
/* PGDEMOTE_*: pages demoted */
PGDEMOTE_KSWAPD,
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b173a059315c..82c8d804c54c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1923,11 +1923,13 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
struct pglist_data *pgdat;
unsigned long rate_limit;
unsigned int latency, th, def_th;
+ long nr = folio_nr_pages(folio);
pgdat = NODE_DATA(dst_nid);
if (pgdat_free_space_enough(pgdat)) {
/* workload changed, reset hot threshold */
pgdat->nbp_threshold = 0;
+ mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE_NRL, nr);
return true;
}
@@ -1941,8 +1943,7 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
if (latency >= th)
return false;
- return !numa_promotion_rate_limit(pgdat, rate_limit,
- folio_nr_pages(folio));
+ return !numa_promotion_rate_limit(pgdat, rate_limit, nr);
}
this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 71cd1ceba191..e74f0b2a1021 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1280,6 +1280,7 @@ const char * const vmstat_text[] = {
#ifdef CONFIG_NUMA_BALANCING
[I(PGPROMOTE_SUCCESS)] = "pgpromote_success",
[I(PGPROMOTE_CANDIDATE)] = "pgpromote_candidate",
+ [I(PGPROMOTE_CANDIDATE_NRL)] = "pgpromote_candidate_nrl",
#endif
[I(PGDEMOTE_KSWAPD)] = "pgdemote_kswapd",
[I(PGDEMOTE_DIRECT)] = "pgdemote_direct",
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v3] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting
2025-09-01 9:01 ` [PATCH v3] " Ruan Shiyang
@ 2025-09-01 11:09 ` Huang, Ying
2025-09-01 19:59 ` Andrew Morton
1 sibling, 0 replies; 7+ messages in thread
From: Huang, Ying @ 2025-09-01 11:09 UTC (permalink / raw)
To: Ruan Shiyang
Cc: linux-mm, linux-kernel, lkp, akpm, y-goto, mingo, peterz,
juri.lelli, vincent.guittot, dietmar.eggemann, rostedt, mgorman,
vschneid, Li Zhijian, Vlastimil Babka, Ben Segall, stable
Ruan Shiyang <ruansy.fnst@fujitsu.com> writes:
> Goto-san reported confusing pgpromote statistics where the
> pgpromote_success count significantly exceeded pgpromote_candidate.
>
> On a system with three nodes (nodes 0-1: DRAM 4GB, node 2: NVDIMM 4GB):
> # Enable demotion only
> echo 1 > /sys/kernel/mm/numa/demotion_enabled
> numactl -m 0-1 memhog -r200 3500M >/dev/null &
> pid=$!
> sleep 2
> numactl memhog -r100 2500M >/dev/null &
> sleep 10
> kill -9 $pid # terminate the 1st memhog
> # Enable promotion
> echo 2 > /proc/sys/kernel/numa_balancing
>
> After a few seconds, we observeed `pgpromote_candidate < pgpromote_success`
> $ grep -e pgpromote /proc/vmstat
> pgpromote_success 2579
> pgpromote_candidate 0
>
> In this scenario, after terminating the first memhog, the conditions for
> pgdat_free_space_enough() are quickly met, and triggers promotion.
> However, these migrated pages are only counted for in PGPROMOTE_SUCCESS,
> not in PGPROMOTE_CANDIDATE.
>
> To solve these confusing statistics, introduce PGPROMOTE_CANDIDATE_NRL to
> count the missed promotion pages. And also, not counting these pages into
> PGPROMOTE_CANDIDATE is to avoid changing the existing algorithm or
> performance of the promotion rate limit.
>
> Link: https://lkml.kernel.org/r/20250729035101.1601407-1-ruansy.fnst@fujitsu.com
> Co-developed-by: Li Zhijian <lizhijian@fujitsu.com>
> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
> Signed-off-by: Ruan Shiyang <ruansy.fnst@fujitsu.com>
> Reported-by: Yasunori Gotou (Fujitsu) <y-goto@fujitsu.com>
> Suggested-by: Huang Ying <ying.huang@linux.alibaba.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
LGTM, feel free to add my
Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com>
in the future versions.
[snip]
---
Best Regards,
Huang, Ying
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting
2025-09-01 9:01 ` [PATCH v3] " Ruan Shiyang
2025-09-01 11:09 ` Huang, Ying
@ 2025-09-01 19:59 ` Andrew Morton
2025-09-01 20:34 ` Vlastimil Babka
1 sibling, 1 reply; 7+ messages in thread
From: Andrew Morton @ 2025-09-01 19:59 UTC (permalink / raw)
To: Ruan Shiyang
Cc: linux-mm, linux-kernel, lkp, ying.huang, y-goto, mingo, peterz,
juri.lelli, vincent.guittot, dietmar.eggemann, rostedt, mgorman,
vschneid, Li Zhijian, Vlastimil Babka, Ben Segall, stable
On Mon, 1 Sep 2025 17:01:22 +0800 Ruan Shiyang <ruansy.fnst@fujitsu.com> wrote:
> Goto-san reported confusing pgpromote statistics where the
> pgpromote_success count significantly exceeded pgpromote_candidate.
>
> On a system with three nodes (nodes 0-1: DRAM 4GB, node 2: NVDIMM 4GB):
> # Enable demotion only
> echo 1 > /sys/kernel/mm/numa/demotion_enabled
> numactl -m 0-1 memhog -r200 3500M >/dev/null &
> pid=$!
> sleep 2
> numactl memhog -r100 2500M >/dev/null &
> sleep 10
> kill -9 $pid # terminate the 1st memhog
> # Enable promotion
> echo 2 > /proc/sys/kernel/numa_balancing
>
> After a few seconds, we observeed `pgpromote_candidate < pgpromote_success`
> $ grep -e pgpromote /proc/vmstat
> pgpromote_success 2579
> pgpromote_candidate 0
>
> In this scenario, after terminating the first memhog, the conditions for
> pgdat_free_space_enough() are quickly met, and triggers promotion.
> However, these migrated pages are only counted for in PGPROMOTE_SUCCESS,
> not in PGPROMOTE_CANDIDATE.
>
> To solve these confusing statistics, introduce PGPROMOTE_CANDIDATE_NRL to
> count the missed promotion pages. And also, not counting these pages into
> PGPROMOTE_CANDIDATE is to avoid changing the existing algorithm or
> performance of the promotion rate limit.
>
> ...
>
It would be good to have a Fixes: here, to tell people how far back to
backport it.
Could be either c6833e10008f or c959924b0dc5 afaict. I'll go with
c6833e10008f, OK?
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting
2025-09-01 19:59 ` Andrew Morton
@ 2025-09-01 20:34 ` Vlastimil Babka
2025-09-01 21:00 ` Andrew Morton
0 siblings, 1 reply; 7+ messages in thread
From: Vlastimil Babka @ 2025-09-01 20:34 UTC (permalink / raw)
To: Andrew Morton, Ruan Shiyang
Cc: linux-mm, linux-kernel, lkp, ying.huang, y-goto, mingo, peterz,
juri.lelli, vincent.guittot, dietmar.eggemann, rostedt, mgorman,
vschneid, Li Zhijian, Ben Segall, stable
On 9/1/25 21:59, Andrew Morton wrote:
> On Mon, 1 Sep 2025 17:01:22 +0800 Ruan Shiyang <ruansy.fnst@fujitsu.com> wrote:
>
>> Goto-san reported confusing pgpromote statistics where the
>> pgpromote_success count significantly exceeded pgpromote_candidate.
>>
>> On a system with three nodes (nodes 0-1: DRAM 4GB, node 2: NVDIMM 4GB):
>> # Enable demotion only
>> echo 1 > /sys/kernel/mm/numa/demotion_enabled
>> numactl -m 0-1 memhog -r200 3500M >/dev/null &
>> pid=$!
>> sleep 2
>> numactl memhog -r100 2500M >/dev/null &
>> sleep 10
>> kill -9 $pid # terminate the 1st memhog
>> # Enable promotion
>> echo 2 > /proc/sys/kernel/numa_balancing
>>
>> After a few seconds, we observeed `pgpromote_candidate < pgpromote_success`
>> $ grep -e pgpromote /proc/vmstat
>> pgpromote_success 2579
>> pgpromote_candidate 0
>>
>> In this scenario, after terminating the first memhog, the conditions for
>> pgdat_free_space_enough() are quickly met, and triggers promotion.
>> However, these migrated pages are only counted for in PGPROMOTE_SUCCESS,
>> not in PGPROMOTE_CANDIDATE.
>>
>> To solve these confusing statistics, introduce PGPROMOTE_CANDIDATE_NRL to
>> count the missed promotion pages. And also, not counting these pages into
>> PGPROMOTE_CANDIDATE is to avoid changing the existing algorithm or
>> performance of the promotion rate limit.
>>
>> ...
>>
>
> It would be good to have a Fixes: here, to tell people how far back to
> backport it.
>
> Could be either c6833e10008f or c959924b0dc5 afaict. I'll go with
> c6833e10008f, OK?
LGTM as a helpful pointer, but I don't think Cc: stable is necessary for
"admin might be confused" kind of thing if that's there since 6.1 and only
came up now.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting
2025-09-01 20:34 ` Vlastimil Babka
@ 2025-09-01 21:00 ` Andrew Morton
0 siblings, 0 replies; 7+ messages in thread
From: Andrew Morton @ 2025-09-01 21:00 UTC (permalink / raw)
To: Vlastimil Babka
Cc: Ruan Shiyang, linux-mm, linux-kernel, lkp, ying.huang, y-goto,
mingo, peterz, juri.lelli, vincent.guittot, dietmar.eggemann,
rostedt, mgorman, vschneid, Li Zhijian, Ben Segall, stable
On Mon, 1 Sep 2025 22:34:32 +0200 Vlastimil Babka <vbabka@suse.cz> wrote:
> > Could be either c6833e10008f or c959924b0dc5 afaict. I'll go with
> > c6833e10008f, OK?
>
> LGTM as a helpful pointer, but I don't think Cc: stable is necessary for
> "admin might be confused" kind of thing if that's there since 6.1 and only
> came up now.
OK, thanks.
^ permalink raw reply [flat|nested] 7+ messages in thread
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[not found] <20250729035101.1601407-1-ruansy.fnst@fujitsu.com>
2025-09-01 2:05 ` [PATCH v2] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting Ruan Shiyang
2025-09-01 8:04 ` Vlastimil Babka
2025-09-01 9:01 ` [PATCH v3] " Ruan Shiyang
2025-09-01 11:09 ` Huang, Ying
2025-09-01 19:59 ` Andrew Morton
2025-09-01 20:34 ` Vlastimil Babka
2025-09-01 21:00 ` Andrew Morton
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