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Wed, 23 Jul 2025 11:09:23 +0800 From: "Huang, Ying" To: Ruan Shiyang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, lkp@intel.com, akpm@linux-foundation.org, y-goto@fujitsu.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, vschneid@redhat.com, Li Zhijian , Ben Segall Subject: Re: [PATCH RFC v3] mm: memory-tiering: Fix PGPROMOTE_CANDIDATE counting In-Reply-To: <20250722141650.1821721-1-ruansy.fnst@fujitsu.com> (Ruan Shiyang's message of "Tue, 22 Jul 2025 22:16:50 +0800") References: <20250722141650.1821721-1-ruansy.fnst@fujitsu.com> Date: Wed, 23 Jul 2025 11:09:21 +0800 Message-ID: <87cy9r38ny.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspam-User: X-Rspamd-Queue-Id: 2F26E40003 X-Rspamd-Server: rspam06 X-Stat-Signature: 6ee66ytryfentpbhhshhh97yjz5hkg7n X-HE-Tag: 1753240167-218705 X-HE-Meta: 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 uQmkkG2S 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Ruan Shiyang writes: > From: Li Zhijian > > === > Changes since v2: > 1. According to Huang's suggestion, add a new stat to not count these > pages into PGPROMOTE_CANDIDATE, to avoid changing the rate limit > mechanism. > === This isn't the popular place for changelog, please refer to other patch email. > 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_NOLIMIT 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. > > Perhaps PGPROMOTE_CANDIDATE_NOLIMIT is not well named, please comment if > you have a better idea. Yes. Naming is hard. I guess that the name comes from the promotion that isn't rate limited. I have asked Deepseek that what is the good abbreviation for "not rate limited". Its answer is "NRL". I don't know whether it's good. However, "NOT_RATE_LIMITED" appears too long. > > The empty line is unnecessary. > Cc: Huang Ying Suggested-by: Huang Ying > Cc: Ingo Molnar > Cc: Peter Zijlstra > Cc: Juri Lelli > Cc: Vincent Guittot > Cc: Dietmar Eggemann > Cc: Steven Rostedt > Cc: Ben Segall > Cc: Mel Gorman > Cc: Valentin Schneider > Reported-by: Yasunori Gotou (Fujitsu) > Signed-off-by: Li Zhijian > Signed-off-by: Ruan Shiyang > --- > include/linux/mmzone.h | 2 ++ > kernel/sched/fair.c | 6 ++++-- > mm/vmstat.c | 1 + > 3 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 283913d42d7b..6216e2eecf3b 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -231,6 +231,8 @@ enum node_stat_item { > #ifdef CONFIG_NUMA_BALANCING > PGPROMOTE_SUCCESS, /* promote successfully */ > PGPROMOTE_CANDIDATE, /* candidate pages to promote */ > + PGPROMOTE_CANDIDATE_NOLIMIT, /* candidate pages without considering > + * hot threshold */ > #endif > /* PGDEMOTE_*: pages demoted */ > PGDEMOTE_KSWAPD, > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 7a14da5396fb..12dac3519c49 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1940,11 +1940,14 @@ 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_NOLIMIT, > + nr); > return true; > } > > @@ -1958,8 +1961,7 @@ 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..ca44a2dd5497 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_nolimit", > #endif > "pgdemote_kswapd", > "pgdemote_direct", --- Best Regards, Huang, Ying