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Tue, 06 Jan 2026 23:28:40 -0800 (PST) Date: Wed, 7 Jan 2026 07:28:14 +0000 In-Reply-To: <20260107072814.2324646-1-bingjiao@google.com> Mime-Version: 1.0 References: <20260107072814.2324646-1-bingjiao@google.com> X-Mailer: git-send-email 2.52.0.358.g0dd7633a29-goog Message-ID: <20260107072814.2324646-3-bingjiao@google.com> Subject: [PATCH v1 2/2] mm/vmscan: select the closest perferred node in demote_folio_list() From: Bing Jiao To: linux-mm@kvack.org Cc: Bing Jiao , Andrew Morton , Johannes Weiner , David Hildenbrand , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Axel Rasmussen , Yuanchu Xie , Wei Xu , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Queue-Id: 7CD1DC0004 X-Rspamd-Server: rspam04 X-Stat-Signature: 3aecymiu51miy3f71dcig19o99xs9y4h X-HE-Tag: 1767770922-642686 X-HE-Meta: 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 5BY1WShQ 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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: The preferred demotion node should be the one closest to the source node to minimize migration latency. However, if the preferred node is not set in mems_allowed, demote_folio_list() currently randomly select one from allowed nodes as the new preferred node. This can result in selecting a very distant node. Update demote_folio_list() to traverse the demotion targets hierarchically until the perferred node is set in mems_allowed, ensuring the perferred target is always the closest available node. Signed-off-by: Bing Jiao --- mm/vmscan.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index db2413c4bd26..d452974c946e 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1052,8 +1052,18 @@ static unsigned int demote_folio_list(struct list_head *demote_folios, if (nodes_empty(allowed_mask)) return false; - if (!node_isset(target_nid, allowed_mask)) - target_nid = node_random(&allowed_mask); + while (target_nid != NUMA_NO_NODE && + !node_isset(target_nid, allowed_mask)) { + /* Get the preferred demotion target from the next tier. */ + target_nid = next_demotion_node(target_nid); + } + + /* + * The perferred node query is subject to race conditions such as + * nodes in the next tier are hot-unplugged. + */ + if (target_nid == NUMA_NO_NODE) + return 0; mtc.nid = target_nid; /* Demotion ignores all cpuset and mempolicy settings */ -- 2.52.0.358.g0dd7633a29-goog