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 F16B9405C23 for ; Mon, 15 Jun 2026 15:32:25 +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=1781537547; cv=none; b=ECkQ6B3z7U4MWYhJ1mev64AQENn6vfIHvMDtgBIWxBZO8Jfl56g5ZymgpQ6MsV0CA/u2QgIVufiFClbDcrQ66iCZ68Vshbz/7HM2CHP62wpiEgDOBaoxbIRn2ZiABKVxh3gvJ0hzxlLaq87tI2KAHhZMk5NtKBFwz7xMEGc15Z4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781537547; c=relaxed/simple; bh=sqL+H21/KV4vs4NMxHSLF0Ok3y2R70ulBAu2NsY2P9o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ezVwiiFVNT5lvrkMVC5evbPQFTApr4asCwGdnk2+g0fvow0cfVYPTDEl/hXs1MpIaNeW6cjVGqL52o6tOVSBtoKw/lWwFr35uzRQ6YXZFpypDv7w1B33LmQpVJddHDKHRVXopOO8q0zGlwJwDfOJ9jhfqp1dD3IyNEFoK9yHLtk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hP1Ne2qN; 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="hP1Ne2qN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9BDD91F000E9; Mon, 15 Jun 2026 15:32:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781537545; bh=eYcJ6fLaq5tKdXm+fVnBYXVTSD6DAPvjOt+eyv2DNuA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=hP1Ne2qN+hrYjUHpA7Htuuox2O0MJtRp4Ylsq9g2xYTR7QFUIFjWQ+3300p+SLghM Kq65moRCtt0LMSyAembSuLfyqj1GtYgtkwAoD80pNfXTpeAnbuYCkCWlNfaXpGETnr hIIlyA7AmVS5z5TaUogu7Ila9aOnG042qJY1njoLcnW6mtD/aFUw2cEtgJX799zZxU gDYyokzQgJeypDqtnYBFv7ofo+dyQZOA8YEnWFS6KdFvDfaO42g8urTTap0sU7KP8b +Jda2N/9yVykOc9x0gCUZuCFPRWwZRgw6r5uATS5twIchbdRPqyM2OqD8fK/zytZay k2y+G3NjXULWQ== Message-ID: <87b8a714-e2bd-449d-9560-c181e927497a@kernel.org> Date: Mon, 15 Jun 2026 17:32:19 +0200 Precedence: bulk X-Mailing-List: oe-lkp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [linux-next:master] [vmalloc] 60ced5818f: stress-ng.shm.ops_per_sec 7.2% regression To: Yeoreum Yun , kernel test robot Cc: Ryan Roberts , oe-lkp@lists.linux.dev, lkp@intel.com, Andrew Morton , Muhammad Usama Anjum , Vlastimil Babka , Zi Yan , Uladzislau Rezki , Brendan Jackman , David Sterba , Johannes Weiner , Liam Howlett , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Nick Terrell , Suren Baghdasaryan , Vishal Moola , linux-mm@kvack.org References: <202606022131.112319f2-lkp@intel.com> 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit >>> -- >>> 0-DAY CI Kernel Test Service >>> https://github.com/intel/lkp-tests/wiki >> >> Thanks. I'll check it. Thanks for digging into the details! > > Looking at the patch [1], the regression reported by lkp [2] appears to > be caused by a lack of order-0 pages in the PCP lists, > which increases zone-locked allocations (mm_page_alloc_zone_locked). > > On my reproduced setup (an x86_64 workstation), most pages freed through > free_pages_bulk() were order-2 pages (nr_pages == 4), including > vmalloc-backed stacks. With patch [1], these order-2 pages are returned to > the order-2 PCP lists, unlike commit 4aa4abf1f1 (“mm/page_alloc: optimize free_contig_range()”), > which effectively populated the order-0 PCP lists. > > Since the shmem workload appears to fault memory at PAGE_SIZE granularity, > the reduced availability of order-0 pages in PCP lists seems to increase > zone-locked order-0 allocations, which may explain the regression observed by lkp. > > Performance comparison (5 runs): > - perf stat -e 'kmem:mm_page_alloc_extfrag' --filter 'alloc_order == 0' \ > -e 'kmem:mm_page_alloc_zone_locked' --filter 'order == 0' \ > -e 'kmem:mm_page_alloc' --filter 'order == 0' -- ./repro-script > > Metric 4aa4abf1f1 60ced5818f Difference > > ------------------------------------------------------------------------------------------ > > Zone-locked Allocation Ratio (%) 46.39 ± 0.17% 48.31 ± 0.37% +1.92 pp > > - Ratio = (mm_page_alloc_extfrag + mm_page_alloc_zone_locked) / mm_page_alloc × 100 > - Values are reported as median ± relative half-range across three runs. > > The shmem test appears to handle page faults at PAGE_SIZE granularity, which seems to amplify the impact of the reduced availability of order-0 pages. Okay, so less fragmentation in the PCP results in fallback to the buddy for order-0. Given that we don't split in the PCP and fallback to the buddy, that makes sense. > > > As an experiment, I modified free_pages_bulk() to free pages individually > as order-0 pages when nr_contig <= (1 << PAGE_ALLOC_COSTLY_ORDER). > This restores behavior closer to 4aa4abf1f1 and results in almost > no difference compared to that commit. > > Performance comparison (5 runs) > - ./repro-script > > Metric 4aa4abf1f1 change Difference > ---------------------------------------------------------------------------------- > bogo_ops 656,513 ± 0.34% 656,488 ± 0.23% -25 > > bogo_ops/s (realtime) 10,935.95 ± 0.34% 10,935.86 ± 0.23% -0.09 > > bogo_ops/s (usr+sys time) 220.31 ± 0.40% 219.30 ± 0.21% -1.01 > > The differences are negligible and essentially restore the performance > observed with 4aa4abf1f1. Makes sense. Looking at the original results, I spotted 354997 ± 14% +111.6% 751255 ± 4% meminfo.PageTables So we consumed twice the (process) page tables. Did you also manage to reproduce that or do you have an explanation for that? > > Given that the regression appears to be driven by a synthetic workload that > combines frequent shmem page faults with repeated stack allocation/free operations, > I do not think this is a significant concern for typical real-world workloads. Yeah, if it's "we have less fragmentation", I agree. Using order-2 folios for shmem would likely similarly mitigate the problem I assume. -- Cheers, David