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Tue, 27 Oct 2026 04:32:31 +0000 X-Mizu-Trace-ID: f40ffff1fc2cc39b X-Migadu-Flow: FLOW_OUT From: Ridong Chen To: Andrew Morton , David Hildenbrand Cc: Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Boris Burkov , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shivank Garg , Ridong Chen , Ridong Chen Subject: [PATCH mm-new] mm/migrate: move NR_KERNEL_FILE_PAGES on cross-node migration Date: Tue, 27 Oct 2026 12:32:14 +0800 Message-Id: <20261027043214.2248986-1-ridong.chen@linux.dev> X-Mailer: git-send-email 2.34.1 X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1B6B5A0005 X-Stat-Signature: 1wm3wyhksnr51mp17qfdc7zqjt3biids X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793075552-813763 X-HE-Meta: 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 hAt6vNi2 Ll6xBeHnnU4e9NfDkzdo8b7CWUZqjLWjX9sTvpf6wtT9/Rx1ieeY7Rtp6mS0sSfhjwWKyasJqxzp4jNn/sQAIXS2sVabAD7E03SMChOZnG6NaCa8XNBiv/QscVpziNMoL5rDojk1Gt+F9PGISxrmglV5VAiZfkp89RnJMyekWtVSDHnPaVuL6u1QOjgYMNqXRQ+Y40SozL4j7j0Mk6c0CST+fdoD3zoNADsi1zztCQhym3uNjv+H1z8iubpKOX1Os92KSVFCxjssj2uZlqzfTCNU8nxY35i25SEojmQMW/KBZzKCdC57pf6XULoihnB9S+3Eq60ND7pOKt/31O2gK2uvLOo2qecgIfk8WCfdsM6dvWVRm9LZPovnaTLY4kXZz//t8jUA2fdwI6Ro= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 From: Ridong Chen NR_KERNEL_FILE_PAGES counts page cache folios of mappings flagged AS_KERNEL_FILE (currently the btrfs btree inode). It is a per-node counter: filemap_add_folio() adds to folio_pgdat() of the new folio and filemap_unaccount_folio() subtracts from folio_pgdat() of the folio being removed. __folio_migrate_mapping() does not move it when such a folio is migrated to another node, so the source node keeps the count forever and the destination node underflows once the folio is freed. btree folios are migratable through btree_migrate_folio(), so demotion, DAMON-based migration (DAMOS_MIGRATE_{HOT,COLD}) or memory offlining all hit this. Reproducer, on a QEMU guest with two memory tiers (node0 is DRAM with all CPUs, node1 is a CPU-less slower node described via HMAT) and /sys/kernel/mm/numa/demotion_enabled set: 1. mount a btrfs and create 20000 empty files, so that btree folios are cached on node0; 2. echo 2G > /sys/devices/system/node/node0/reclaim, which demotes them to node1; 3. umount and drop caches. nr_kernel_file_pages in /sys/devices/system/node/nodeN/vmstat after each step: without this patch with this patch node0 node1 node0 node1 1. cached 1868 0 1868 0 2. demoted 1868 0 36 1832 3. dropped 1832 0 (*) 0 0 (*) the counter has underflowed to -1832; negative values read as 0. The global value in /proc/vmstat is 0 after step 3 in both cases. Move it together with the other node-keyed page cache counters. It is a node-only counter, so use the node accessor, matching how it is accounted elsewhere. Interrupts are disabled here, as for the zone counters below. This was pointed out by Shivank while reviewing the NR_FILE_THPS fix for the same function. Fixes: e3a9ac4e866e ("mm: add vmstat for kernel_file pages") Suggested-by: Shivank Garg Assisted-by: LLM Signed-off-by: Ridong Chen --- mm/migrate.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/migrate.c b/mm/migrate.c index 99e3026e3126..f829c5017c96 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -705,6 +705,12 @@ static int __folio_migrate_mapping(struct address_space *mapping, mod_lruvec_state(old_lruvec, NR_FILE_THPS, -nr); mod_lruvec_state(new_lruvec, NR_FILE_THPS, nr); } + if (test_bit(AS_KERNEL_FILE, &mapping->flags)) { + __mod_node_page_state(oldzone->zone_pgdat, + NR_KERNEL_FILE_PAGES, -nr); + __mod_node_page_state(newzone->zone_pgdat, + NR_KERNEL_FILE_PAGES, nr); + } #ifdef CONFIG_SWAP if (folio_test_swapcache(folio)) { mod_lruvec_state(old_lruvec, NR_SWAPCACHE, -nr); -- 2.34.1