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Message-ID: <10659223-9bbe-468e-b458-ccd421590b7a@fujitsu.com>
Date: Fri, 29 Aug 2025 17:18:55 +0800
From: Shiyang Ruan <ruansy.fnst@...itsu.com>
To: Vlastimil Babka <vbabka@...e.cz>, akpm@...ux-foundation.org,
linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, lkp@...el.com,
ying.huang@...ux.alibaba.com, y-goto@...itsu.com, mingo@...hat.com,
peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
vschneid@...hat.com, Ben Segall <bsegall@...gle.com>,
Li Zhijian <lizhijian@...itsu.com>
Subject: Re: [PATCH v1] mm: memory-tiering: Fix PGPROMOTE_CANDIDATE counting
在 2025/8/29 17:08, Vlastimil Babka 写道:
> On 7/29/25 05:51, Ruan Shiyang wrote:
>
> A process nit: your RFC v3 had:
>
> From: Li Zhijian <lizhijian@...itsu.com>
>
> and this one doesn't.
>
>> 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 this confusing statistics, introduce this 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.
>>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Juri Lelli <juri.lelli@...hat.com>
>> Cc: Vincent Guittot <vincent.guittot@...aro.org>
>> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Ben Segall <bsegall@...gle.com>
>> Cc: Mel Gorman <mgorman@...e.de>
>> Cc: Valentin Schneider <vschneid@...hat.com>
>> Reported-by: Yasunori Gotou (Fujitsu) <y-goto@...itsu.com>
>> Suggested-by: Huang Ying <ying.huang@...ux.alibaba.com>
>> Signed-off-by: Li Zhijian <lizhijian@...itsu.com>
>
> So the S-o-b from Li doesn't match anything now.
> You can either reinstate that "From: Li ..." or add a "Co-developed-by: Li
> ..." right above the "S-o-b: Li ..." - that's for you two to decide who is
> the main author.
Thanks for pointing out. I wasn't aware of this.
I'd like to add a Co-developed-by tag:
Co-developed-by: Li Zhijian
Then, should I resend a new version with is tag added? Or you will do that for me?
--
Best regards,
Ruan.
>
> More details in Documentation/process/submitting-patches.rst
>
>> Signed-off-by: Ruan Shiyang <ruansy.fnst@...itsu.com>
>> ---
>> Changes since RFC v3:
>> 1. change the naming of new added stat to PGPROMOTE_CANDIDATE_NRL.
>> 2. improve the description of the two stats.
>> ---
>> 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 283913d42d7b..4345996a7d5a 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -230,7 +230,21 @@ 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 7a14da5396fb..4022c9c1f346 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -1940,11 +1940,13 @@ 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;
>> }
>>
>> @@ -1958,8 +1960,7 @@ 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 a78d70ddeacd..bb0d2b330dd5 100644
>> --- a/mm/vmstat.c
>> +++ b/mm/vmstat.c
>> @@ -1272,6 +1272,7 @@ const char * const vmstat_text[] = {
>> #ifdef CONFIG_NUMA_BALANCING
>> "pgpromote_success",
>> "pgpromote_candidate",
>> + "pgpromote_candidate_nrl",
>> #endif
>> "pgdemote_kswapd",
>> "pgdemote_direct",
>
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