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b=N2nZhoK/Q21LIbrSnildvG4xpGY+k68+D5kfaDcIxkTjgeF3IUDsP7xsKzTzMKStp GHMPTe3JVyTaKevz1ZPsATz3LZevBNmkcINf5YYDPMuSccRpOz243d4StJy5RGtIeb xP0OlHp/akySD5KbATJbrZ5IaVKH9SRieMRW8uBg= Date: Mon, 1 Sep 2025 12:59:17 -0700 From: Andrew Morton To: Ruan Shiyang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, lkp@intel.com, ying.huang@linux.alibaba.com, 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 Message-Id: <20250901125917.e9792e5d0df12ba1c552c537@linux-foundation.org> In-Reply-To: <20250901090122.124262-1-ruansy.fnst@fujitsu.com> References: <20250729035101.1601407-1-ruansy.fnst@fujitsu.com> <20250901090122.124262-1-ruansy.fnst@fujitsu.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 19CB820005 X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: 8fbr1zm9erfgqexezeg6hh7q46qnuarx X-HE-Tag: 1756756759-680994 X-HE-Meta: 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 qMMbV3Ax 41z5tK8bVpidlMXxLoeBp9eKukhcquS3RFYD/h5lBQzmf8nCyhcFw+3N+FhjY+qt7rpf1WbY+3y9E12Fwk4EsdT2Zr3+J5XnwOi/p/RGRaUo/EcESc+zC1ms2H0I7vMgNWlCE2feSXodNwjEq5pRbXzY81XPBgJyFQ9yQwemo8agtDzILSdqHXqihvXYykmEa2qxLOsAJE09Fy5MGlmTfK0HhYfx05Z/AmTidml5CwgJaVDF2dHmH9LAtAjW2yNld574mlvp3lbsb8hCmyD/GhU+FzgpXyig0JvyN85qpk8vw1FC72DK97hOxLwaSDoEATC1C 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: On Mon, 1 Sep 2025 17:01:22 +0800 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. > > ... > 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?