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bh=3iZQBCEvkqNhfR7+tg1Golqh8qIukiggVHmycsiCiLQ=; b=r5OyUEQO8cMHcZTUPvyIEbMd39poRY5Wl5CME0DlPq+2w9w0qsAIjR368aIhLYvdkfZ4yz bDqE5CHggak/mEBA== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id B4E4B1378C; Mon, 1 Sep 2025 08:04:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id /QHzKpxTtWgXUwAAD6G6ig (envelope-from ); Mon, 01 Sep 2025 08:04:44 +0000 Message-ID: Date: Mon, 1 Sep 2025 10:04:44 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: memory-tiering: fix PGPROMOTE_CANDIDATE counting To: Ruan Shiyang , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, lkp@intel.com, ying.huang@linux.alibaba.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 , stable@vger.kernel.org References: <20250729035101.1601407-1-ruansy.fnst@fujitsu.com> <20250901020538.3960468-1-ruansy.fnst@fujitsu.com> Content-Language: en-US From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+] X-Spam-Score: -4.51 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 > 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 > --- > 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.