From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F265D48034D for ; Thu, 2 Jul 2026 13:00:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782997215; cv=none; b=SaInUxC4n+5m0mZIUh/Uwzqe9A1XiMZpOH/nfB3De70AnMkQGLWjdbWh1JhVdzQWk78vjg8YfHmS593IUeOPXkifiBr+pNiaRFg5VNivBOzeUcv1Udo2MUrur764/kvXoX1Ar8ZiNOJ1p5ZY3q8OnALCCoJMj/d1GdjUFGa6d0Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782997215; c=relaxed/simple; bh=njafAkzPQlglm5QrSeq6P9qi5wDwd9AZfm08Xx5bElo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OgwdIm8+K1mRctFS7uYCrvpGhwpHoU5TYgQdqXKErho70GUu1QJZuOcflAM2YkU17j7FyKij0wUB1kifvhSep3aC7WaFVy9HPmJ4DJ24Ww7IbOaIrzyZhWo1lI7eYucpvQI9+ge9RlS11WzJoMeTI2SehH/FWDFhKAS96E9N1e0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a/HCRW/f; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="a/HCRW/f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D452E1F000E9; Thu, 2 Jul 2026 13:00:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782997213; bh=pQ814jvzg7n+lJelOqWgsVPCnWqUGa/F5vmYshJwnpg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=a/HCRW/f7deDyKrFTRnaWSMR8PZ1g+mBK9qjkzm/3cNPVfKwcSC1o9EbreS9GRtKy LFkAmMnL40SlppydW8n4mH3xRGGGSnQiaBO8J9S3F6AAqu6LAXQf8otIhsNqF0Xjzh AMooPVsMHxMR3xiRxsysOZaJdfdV2JN7DzYJOdc96mNch0ueuUbsoWUHTps/vcTsNS 47AGSsJRvh6yHTCNMWyOUvrOlnK/E3uH/lxzc9MJEa/8hrJ5RDL+CgLi95ccl+nYZb ujMgnj4DrHjeeO9spmBWcgoipWqWqYGFDnBFgT3+hdzJFzBMim8piY6xFG67rsAev1 kwrq6NYmqEGAw== Message-ID: <6a81273c-6d5c-4811-a6a6-e1e8a3a47b97@kernel.org> Date: Thu, 2 Jul 2026 15:00:08 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: allow smaller large folios to use lru_cache To: "Barry Song (Xiaomi)" , akpm@linux-foundation.org, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang References: <20260702122342.26721-1-baohua@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260702122342.26721-1-baohua@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/2/26 14:23, Barry Song (Xiaomi) wrote: > For a system which primarily uses smaller orders for large folios, > it could be beneficial to enable lru_cache to avoid lock contention. > > For large folios with higher orders, the number of folios involved > would be small, so the contention is less significant. > > The following small program runs on a system with 16 KiB > mTHP enabled. > > #include > #include > #include > > #define NUM_THREADS 20 > #define MEM_SIZE (16 * 1024 * 1024) > #define LOOP_COUNT 1000 > > void* thread_worker(void* arg) { > void *addr = mmap(NULL, MEM_SIZE, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > for (int i = 0; i < LOOP_COUNT; i++) { > memset(addr, 0x55, MEM_SIZE); > madvise(addr, MEM_SIZE, MADV_DONTNEED); > } > > munmap(addr, MEM_SIZE); > pthread_exit(NULL); > } > > int main() { > pthread_t threads[NUM_THREADS]; > > for (long t = 0; t < NUM_THREADS; t++) { > pthread_create(&threads[t], NULL, thread_worker, (void*)t); > } > > for (int t = 0; t < NUM_THREADS; t++) { > pthread_join(threads[t], NULL); > } > > return 0; > } > > Before patch: > root@barry-desktop:/home/barry# time ./a.out > > real 0m20.233s > user 0m21.739s > sys 6m21.143s > > Perf lock report: > Name acquired contended avg wait total wait max wait min wait > > 21158662 21158662 29.20 us 10.30 m 67.83 us 884 ns > 13547 13547 14.68 us 198.93 ms 135.39 us 982 ns > rcu_state 41 41 1.83 us 75.21 us 3.46 us 1.27 us > rcu_state 34 34 1.83 us 62.09 us 2.60 us 1.16 us > 5 5 21.31 us 106.57 us 25.77 us 18.17 us > 5 5 3.01 us 15.07 us 5.19 us 1.53 us > 3 3 6.42 us 19.26 us 9.63 us 4.22 us > 3 3 4.20 us 12.61 us 7.45 us 2.10 us > 2 2 5.03 us 10.06 us 7.88 us 2.18 us > 2 2 2.79 us 5.59 us 3.34 us 2.25 us > 1 1 4.70 us 4.70 us 4.70 us 4.70 us > 1 1 9.77 us 9.77 us 9.77 us 9.77 us > > After patch: > root@barry-desktop:/home/barry# time ./a.out > > real 0m17.796s > user 0m24.962s > sys 5m28.774s > > Perf lock report: > Name acquired contended avg wait total wait max wait min wait > > 1407013 1407013 25.44 us 35.80 s 127.83 us 972 ns > 845113 845113 47.96 us 40.54 s 152.86 us 1.21 us > rcu_state 1920 1920 5.87 us 11.27 ms 25.02 us 1.76 us > rcu_state 1889 1889 5.80 us 10.96 ms 30.35 us 1.61 us > 140 140 3.97 us 555.52 us 12.51 us 1.20 us > 10 10 61.34 us 613.42 us 96.90 us 44.48 us > 8 8 24.03 us 192.26 us 37.64 us 6.95 us > 8 8 12.32 us 98.56 us 25.55 us 4.16 us > > Both system time and lock contention are noticeably reduced. > > Cc: David Hildenbrand > Cc: Lorenzo Stoakes > Cc: Zi Yan > Cc: Baolin Wang > Cc: Liam R. Howlett > Cc: Nico Pache > Cc: Ryan Roberts > Cc: Dev Jain > Cc: Lance Yang > Signed-off-by: Barry Song (Xiaomi) > --- > include/linux/swap.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 8f0f68e245ba..fce1d84aa2c8 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -322,9 +322,9 @@ static inline bool folio_may_be_lru_cached(struct folio *folio) > /* > * Holding PMD-sized folios in per-CPU LRU cache unbalances accounting. > * Holding small numbers of low-order mTHP folios in per-CPU LRU cache > - * will be sensible, but nobody has implemented and tested that yet. > + * will be sensible. > */ > - return !folio_test_large(folio); > + return folio_order(folio) < PAGE_ALLOC_COSTLY_ORDER; > } > > extern atomic_t lru_disable_count; Not that __wp_can_reuse_large_anon_folio() currently assumes that large folios are not in the LRU cache. -- Cheers, David