From nobody Tue Feb 10 04:12:20 2026 Received: from mail-dl1-f74.google.com (mail-dl1-f74.google.com [74.125.82.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2948E357A33 for ; Wed, 14 Jan 2026 20:53:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768424000; cv=none; b=ldpLLJ9YyaaC6h6fIzR8uXo/tcoWDCdgOGleJNzCEif4JszSmK2lmnmaFGbLCmrMAEQIvnFAitFX7CSg5PQgngE3VB3bYbI8nDK98fV/1KWIJRUMSF2erTYT00KJPONTCp0xv9FHOGeyUBLd8lAyoXZWAXuAjIIZ6tDBMaVfctY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768424000; c=relaxed/simple; bh=9B0HAws0jD6ktvEqCEUvq5OCM9p89Vzub9JqPk8brWM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=cNvFDAhbbHUiFM0tzMRaP0Tk1s2yF9v6bfZU2r2sRmc6B2PrETgwxJvgnL0lxX1mRL6Tni3KtEK81K9wRV9/cfYS3tqdwJKtBb0vVaUDC9bjpG+I7FEJnErnCJaDvMRw6OtSE969Uc5RPJr4slBVwqzA24RcX9q1QyPfYoZNTlw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--bingjiao.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=MV+dwNDx; arc=none smtp.client-ip=74.125.82.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--bingjiao.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="MV+dwNDx" Received: by mail-dl1-f74.google.com with SMTP id a92af1059eb24-1233b91de6bso349207c88.1 for ; Wed, 14 Jan 2026 12:53:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1768423989; x=1769028789; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=CCsRJ41+Ggq8G+xRjLn+/BFhG0UFmGF8M8WZhyAL+Ls=; b=MV+dwNDx3WDh5Q2Hcv0ZS66h9V3205AxXvfXKMhmwuPFRI4TOcJf6jy6Ljo1qNNeFV TlDQ+XYPPwL1vBVDn8vM6l6fO8SJ8PI6OhzFxU93JqVDmtwULkL5VtfR9LLb2GmzCa1A R3JyUsmCENAPCgwgOSeI3GXAelLgshVQvEdcRc8FViP1RkKkqGN1hLzFCKU22s6K34F5 1JGiWcJeMxvpwgtWIRLjAPK+qBj2DXGpTVVal+9V5BVABVghTk7O4q32gokZxw+Qvo/U ZrWcrCSqQ0JpJWLSgZyD1fFZbXFbZ4qLH91achfhBEcFTPJYx0GkCViIucRZ2tWU//jN vYiA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1768423989; x=1769028789; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=CCsRJ41+Ggq8G+xRjLn+/BFhG0UFmGF8M8WZhyAL+Ls=; b=hWJl14dHFn69HmXLKp817GRmNaXvYPXEbRkPSBg+xt25u1kDXGTJ/roL5TBo2rhzTc aT3y5KsN4EnPWbhyxkD9WfXSi5Hxxk1jkktl/cBSTZY2zP4znKViJaNpoQbq7upBN7Lv hSdUET9CLFQXvRs8ld/8/OaoQRlG3G7YApVtIAcYVsnG+MvH+W6b8weJmMjoItSk4e/V ftH38dS/hPbpx+5qRW8JnPEQvkB+bVYERmPqL269V8YRF54O1ZwC5QdS9guUoJnjk8ni W+T/Oolbyj2OwBELOqqoLoMwQpRUWoXvspPSjQ90n4J4aRdBliOQmn3O62GmDhpj2YjF bSgQ== X-Forwarded-Encrypted: i=1; AJvYcCVVT2g+7ovS2iM80UpmREXeZakqYfS88IYn4JI1UEVuAOj9gehU9u1AGCoCL03WwwDpVlbbqwGmN3hgluk=@vger.kernel.org X-Gm-Message-State: AOJu0YyZllHNeo4syVHLqX3bVCKHYDvq16BY3jX2wVTeM2trrb55cL1G URwrmyR9xp4oaLYAWdmDCil4g3/e0KrwXHYwzzfwoe1egb0Q9ScoW+PqBTBYSYBjVn2ZpRqWbMu t/DxvJOiYlWftJQ== X-Received: from dybic39.prod.google.com ([2002:a05:7300:c727:b0:2a4:612e:b41f]) (user=bingjiao job=prod-delivery.src-stubby-dispatcher) by 2002:a05:701a:ca03:b0:11b:923d:7753 with SMTP id a92af1059eb24-12336a12704mr4017500c88.3.1768423989308; Wed, 14 Jan 2026 12:53:09 -0800 (PST) Date: Wed, 14 Jan 2026 20:53:03 +0000 In-Reply-To: <20260114205305.2869796-1-bingjiao@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260114070053.2446770-1-bingjiao@google.com> <20260114205305.2869796-1-bingjiao@google.com> X-Mailer: git-send-email 2.52.0.457.g6b5491de43-goog Message-ID: <20260114205305.2869796-3-bingjiao@google.com> Subject: [PATCH v9 2/2] mm/vmscan: select the closest perferred node in demote_folio_list() From: Bing Jiao To: bingjiao@google.com Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Axel Rasmussen , Yuanchu Xie , Wei Xu , Johannes Weiner , Qi Zheng , Shakeel Butt , Gregory Price , Joshua Hahn , muchun.song@linux.dev, roman.gushchin@linux.dev, tj@kernel.org, longman@redhat.com, chenridong@huaweicloud.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The preferred demotion node (migration_target_control.nid) should be the one closest to the source node to minimize migration latency. Currently, a discrepancy exists where demote_folio_list() randomly selects an allowed node if the preferred node from next_demotion_node() is not set in mems_effective. To address it, update next_demotion_node() to select a preferred target against allowed nodes; and to return the closest demotion target if all preferred nodes are not in mems_effective via next_demotion_node(). It ensures that the preferred demotion target is consistently the closest available node to the source node. Signed-off-by: Bing Jiao Acked-by: Shakeel Butt --- v7 -> v8: Fix bugs in v7. Remove the while loop of getting the preferred node via next_demotion_node(). Use find_next_best_node() to find the closest demotion target. v8 -> v9: Move allowed node checks and identification of the closest demotion target into next_demotion_node() for better function splitting. include/linux/memory-tiers.h | 6 +++--- mm/memory-tiers.c | 21 ++++++++++++++++----- mm/vmscan.c | 5 ++--- 3 files changed, 21 insertions(+), 11 deletions(-) diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h index 7a805796fcfd..96987d9d95a8 100644 --- a/include/linux/memory-tiers.h +++ b/include/linux/memory-tiers.h @@ -53,11 +53,11 @@ struct memory_dev_type *mt_find_alloc_memory_type(int a= dist, struct list_head *memory_types); void mt_put_memory_types(struct list_head *memory_types); #ifdef CONFIG_MIGRATION -int next_demotion_node(int node); +int next_demotion_node(int node, const nodemask_t *allowed_mask); void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets); bool node_is_toptier(int node); #else -static inline int next_demotion_node(int node) +static inline int next_demotion_node(int node, const nodemask_t *allowed_m= ask) { return NUMA_NO_NODE; } @@ -101,7 +101,7 @@ static inline void clear_node_memory_type(int node, str= uct memory_dev_type *memt } -static inline int next_demotion_node(int node) +static inline int next_demotion_node(int node, const nodemask_t *allowed_m= ask) { return NUMA_NO_NODE; } diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c index 864811fff409..2d6c3754e6a8 100644 --- a/mm/memory-tiers.c +++ b/mm/memory-tiers.c @@ -320,16 +320,17 @@ void node_get_allowed_targets(pg_data_t *pgdat, nodem= ask_t *targets) /** * next_demotion_node() - Get the next node in the demotion path * @node: The starting node to lookup the next node + * @allowed_mask: The pointer to allowed node mask * * Return: node id for next memory node in the demotion path hierarchy * from @node; NUMA_NO_NODE if @node is terminal. This does not keep * @node online or guarantee that it *continues* to be the next demotion * target. */ -int next_demotion_node(int node) +int next_demotion_node(int node, const nodemask_t *allowed_mask) { struct demotion_nodes *nd; - int target; + nodemask_t mask; if (!node_demotion) return NUMA_NO_NODE; @@ -344,6 +345,10 @@ int next_demotion_node(int node) * node_demotion[] reads need to be consistent. */ rcu_read_lock(); + /* Filter out nodes that are not in allowed_mask. */ + nodes_and(mask, nd->preferred, *allowed_mask); + rcu_read_unlock(); + /* * If there are multiple target nodes, just select one * target node randomly. @@ -356,10 +361,16 @@ int next_demotion_node(int node) * caching issue, which seems more complicated. So selecting * target node randomly seems better until now. */ - target =3D node_random(&nd->preferred); - rcu_read_unlock(); + if (!nodes_empty(mask)) + return node_random(&mask); - return target; + /* + * Preferred nodes are not in allowed_mask. Filp bits in + * allowed_mask as used node mask. Then, use it to get the + * closest demotion target. + */ + nodes_complement(mask, *allowed_mask); + return find_next_best_node(node, &mask); } static void disable_all_demotion_targets(void) diff --git a/mm/vmscan.c b/mm/vmscan.c index 5ea1dd2b8cce..7a631de46064 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1048,12 +1048,11 @@ static unsigned int demote_folio_list(struct list_h= ead *demote_folios, if (nodes_empty(allowed_mask)) return 0; - target_nid =3D next_demotion_node(pgdat->node_id); + target_nid =3D next_demotion_node(pgdat->node_id, &allowed_mask); if (target_nid =3D=3D NUMA_NO_NODE) /* No lower-tier nodes or nodes were hot-unplugged. */ return 0; - if (!node_isset(target_nid, allowed_mask)) - target_nid =3D node_random(&allowed_mask); + mtc.nid =3D target_nid; /* Demotion ignores all cpuset and mempolicy settings */ -- 2.52.0.457.g6b5491de43-goog