From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.189 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793075693; b=WAjhNuGofzJf47sxbJQgdNEXrtgOb4HTFTG0aKOBUuBPzE8hS9WBM8Az/LhAXwKKvN6s bRES/9Jd4AlEMizTqnUxPf3E9qupa4AsLzJCOeX+I1tnHi+d29kz7ZYD7ONalyM8OfqdM k880mt+cmk+gV8ZOx1Ih08PhjpOZkAf4yyojgma14pM+YX7NMAxEa+OWP85o9VCL2m76M C6kLSbzjqsmWJP6b5UCegpEAo7pF665vaapVjjxZ9vBJUBvkGJB7spJ5Sbgihue0Yguia PcEvoCsW8xAv/oTmXxXiMUkXvzP3qJHtjZpBymrs9pFoyM1IcHMDWzbWpr3CgIATuBw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793075693; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding; bh=8bPDXwOSDS16plg0sE4B84SdEhQiLrfepkoN/xaCOWc=; b=UrJz9DOg3s6rUsfhJn4LIjExVvd+ug3tVoQwJbPYKHvkRgEXJtbZQ+f73+E/PbjbxuNB wfEj/viVNI9R9VMdZLfcCbyaVApwJzgPRRp1OPuW43lV1Yp46DutkgQKWR1ibwSlyDNcF UbDIJK/VQdJ5GcQ6y8fI/ESzV9efLzzYLvzZaSi9qtUNBRBBABbDMAJpOGcUZpN7PM754 tp4Lns76COlbeHX21kRwvTsDLv3mxJgzGmVm4EqWmt71/ABhWt8x5BhqRLVznrscIHU3+ xtTtvBxf9h8v5wqn1zI3xOpXbAxwd1lUQzPwhrRnPo9am17NRxWJGLf28n1EgjqPLnw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=ZXH+MRud; arc=none smtp.remote-ip=95.215.58.189 Received: from mta1.migadu.com (out-189.mta1.migadu.com [95.215.58.189]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C63D606A31A for ; Tue, 27 Oct 2026 04:34:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 6C63D606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=ZXH+MRud X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=nzg0KAy4r17iWdtc1/Guk/G16m3PL2GLFdlHcOEPTm8=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793075690; v=1; x=1793680490; b=ZXH+MRud0A9N6N3RBKQRDno4784HvX4suabk/vTqyGni5R0GEvknRJ3hwC8RY6qdYzpS8w8z ub8AU3OOyuVar2e0Mq0CWSPKhgysvo7ByyynhxlXatGUGxMQZ/FqnUgFmwNjvZ2w2SHmORsjzUp PiG4OK58ecf0OGzLDj+76xL4= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 7c7d843a2b7f921b; Tue, 27 Oct 2026 04:34:50 +0000 X-Mizu-Trace-ID: 7c7d843a2b7f921b X-Migadu-Flow: FLOW_OUT Message-ID: <1267a0a3-d3fa-49ee-a791-294e62c29bb6@linux.dev> Date: Tue, 27 Oct 2026 12:34:37 +0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate: move NR_FILE_THPS on cross-node migration To: "Garg, Shivank" , "david@kernel.org" , "akpm@linux-foundation.org" Cc: "chenridong@xiaomi.com" , "apopple@nvidia.com" , "ziy@nvidia.com" , "gourry@gourry.net" , "linux-mm@kvack.org" , "matthew.brost@intel.com" , "joshua.hahnjy@gmail.com" , "ying.huang@linux.alibaba.com" , "linux-kernel@vger.kernel.org" , "byungchul@sk.com" , "willy@infradead.org" References: <20261025110209.4105994-1-ridong.chen@linux.dev> <6372d92c7b0ec9c3fef4e803e39e54a36f3aa918.camel@amd.com> From: Ridong Chen In-Reply-To: <6372d92c7b0ec9c3fef4e803e39e54a36f3aa918.camel@amd.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/26/2026 8:51 PM, Garg, Shivank wrote: > On Mon, 2026-10-26 at 11:59 +0100, David Hildenbrand (Arm) wrote: >> On 10/25/26 12:02, Ridong Chen wrote: >>> From: Ridong Chen >>> >>> When a page cache folio is migrated to another node, >>> __folio_migrate_mapping() moves the per-node and per-memcg counters >>> that are keyed off the folio's node: NR_FILE_PAGES, NR_SHMEM, >>> NR_SHMEM_THPS, NR_SWAPCACHE and NR_FILE_DIRTY. NR_FILE_THPS is not >>> moved, although __filemap_add_folio() charges it to the source node and >>> filemap_unaccount_folio() takes it off whatever node the folio lives on >>> when it is removed. >>> >>> Commit 0b52c420350e ("mm: fix shmem THP counters on migration") added >>> the NR_SHMEM_THPS case but not its file-backed counterpart. Now that >>> ext4, xfs, btrfs and erofs can all have PMD-sized page cache folios, >>> migrating them via NUMA balancing, mbind(), migratepages, demotion or >>> memory offlining leaks FileHugePages on the source node and underflows >>> it on the destination, in both /sys/devices/system/node/nodeN/meminfo >>> and memory.numa_stat. The global value is unaffected, which is why this >>> went unnoticed. >>> >>> Reproducer, on a 2-node QEMU guest with THP set to "always": >>> >>> 1. read a 256M ext4 file through a MADV_HUGEPAGE mapping while bound >>> to node 0, so its page cache is 128 PMD-sized folios on node 0; >>> 2. move the mapping to node 1 with mbind(MPOL_MF_MOVE); >>> 3. unmap the file and drop its page cache. >>> >>> nr_file_hugepages in /sys/devices/system/node/nodeN/vmstat after each >>> step (in units of PMD-sized folios): >>> >>> without this patch with this patch >>> node0 node1 node0 node1 >>> 1. cached 128 0 128 0 >>> 2. migrated 128 0 0 128 >>> 3. dropped 128 0 (*) 0 0 >>> >>> (*) the counter has underflowed to -128; negative values read as 0. >>> >>> Without the patch the 128 folios stay accounted to node 0 forever, and >>> every further round adds another 128. The same happens to the per-memcg >>> per-node counter: after step 3, memory.stat of the cgroup shows >>> "file_thp 0", while memory.numa_stat still shows >>> "file_thp N0=268435456 N1=0". With the patch both are 0. >>> >>> Move NR_FILE_THPS together with NR_FILE_PAGES, using the same condition >>> filemap_unaccount_folio() uses to take it off, so that THPs in the swap >>> cache are left alone. >>> >>> Fixes: d68eccad3706 ("mm/filemap: Allow large folios to be added to the page cache") >>> Signed-off-by: Ridong Chen >>> --- >>> Note: prepared with help from an LLM-based assistant (Kiro, claude-opus-5.5). >>> >>> mm/migrate.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/mm/migrate.c b/mm/migrate.c >>> index 7bdcdb57652f..d55f576a2579 100644 >>> --- a/mm/migrate.c >>> +++ b/mm/migrate.c >>> @@ -700,6 +700,10 @@ static int __folio_migrate_mapping(struct address_space *mapping, >>> mod_lruvec_state(old_lruvec, NR_SHMEM_THPS, -nr); >>> mod_lruvec_state(new_lruvec, NR_SHMEM_THPS, nr); >>> } >>> + } else if (!folio_test_swapbacked(folio) && >>> + folio_test_pmd_mappable(folio)) { >>> + mod_lruvec_state(old_lruvec, NR_FILE_THPS, -nr); >>> + mod_lruvec_state(new_lruvec, NR_FILE_THPS, nr); >>> } >> >> Looking at filemap_unaccount_folio(), I was (once again) surprise about the >> different handling. >> >> Key is that we might be migration aonymous folios in the swapcache. >> >> Acked-by: David Hildenbrand (Arm) >> > > filemap_unaccount_folio() also checks for AS_KERNEL_FILE, but > __folio_migrate_mapping() does not. > > Should add this as well? > Good catch, thanks. NR_KERNEL_FILE_PAGES has the same problem, and I could reproduce it by demoting btrfs btree folios to a CPU-less memory tier. Since it was introduced separately by e3a9ac4e866e ("mm: add vmstat for kernel_file pages") and is a node-only counter, I sent it as a separate patch on top of this one: https://lore.kernel.org/20261027043214.2248986-1-ridong.chen@linux.dev -- Best regards Ridong