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Mon, 01 Sep 2025 19:10:12 +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 , Vlastimil Babka , Ben Segall , stable@vger.kernel.org Subject: Re: [PATCH v3] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting In-Reply-To: <20250901090122.124262-1-ruansy.fnst@fujitsu.com> (Ruan Shiyang's message of "Mon, 1 Sep 2025 17:01:22 +0800") References: <20250729035101.1601407-1-ruansy.fnst@fujitsu.com> <20250901090122.124262-1-ruansy.fnst@fujitsu.com> Date: Mon, 01 Sep 2025 19:09:55 +0800 Message-ID: <878qiya0os.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B9E82120010 X-Stat-Signature: ano1cchrckwt4oqsqqkpaahc7yshnqtp X-Rspam-User: X-HE-Tag: 1756725017-842687 X-HE-Meta: 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 2Q4w6evO 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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: > 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 > Signed-off-by: Li Zhijian > Signed-off-by: Ruan Shiyang > Reported-by: Yasunori Gotou (Fujitsu) > Suggested-by: Huang Ying > Acked-by: Vlastimil Babka > 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 > Cc: > Signed-off-by: Andrew Morton LGTM, feel free to add my Reviewed-by: Huang Ying in the future versions. [snip] --- Best Regards, Huang, Ying