From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4D0D6394788 for ; Tue, 12 May 2026 09:31:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778578288; cv=none; b=VP5ZOZgKIfT3lTx4r/y1z8xRaSBoEGR52Dy5FW/WjCMPuBnt76XXdCoGQUtBQOKGH6rKC2yAtwvA2YcbhY9Jup/TLzRjHh9WYqpw8BOFb/Hi48UIq9A48pgH28VpThlLCPkHl7GWWIUKqVcv+r2olSVfjqmT09jhawkCsHUpNQk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778578288; c=relaxed/simple; bh=+GzPz+gI2GYfbiRoN2dqRZqYupazekpJJqvduzi/Bys=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ezknLvbGiiXYIAYCN7kyHoWKo+ZXWtTA2611ZPHnP6UqnEtrK9OfSEaaP4QWTB3D3TTsR4YaBmiqzFDdDxe0aIydbmb8FpgVkFWZyUaML7cOD9Byru+O+YZszu2064E8ppf27w0nVECdnGgE0Ea790QOP6euN2j8rmZHYqQFZZw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lOQB4kHd; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lOQB4kHd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 53301C2BCB0; Tue, 12 May 2026 09:31:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778578287; bh=+GzPz+gI2GYfbiRoN2dqRZqYupazekpJJqvduzi/Bys=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=lOQB4kHdnMEnvNtfahCQ7KZxAsDqwU4jjBbR7Ko5onUAIT09DxFksacSN4l5ed1Ba 23Ama/5TI8gw7dEt3f4rEFniUPO/wEn+9yf/J4rDJ+Edu/eZPYYhF3VOwiYDth8zaA R+W8Rg67C2Iul7zIbFWHemSpfmKe6QkTLsfSW0f5eWGbuBNnuwOSqSilsaoLVibA+M gCwmLCX0RFbW2PQUKx0HrPZcwSxv8G8vPuoJMuZL0D5q6rPoz2f/Q5JkhA81hMWoRd AtoPy2nVKKP+UUvy6WYvw6bEwQ90EIRmtpf1SGBcWUqQ3TtDVHv0QKxBqWtb9lbqkQ 6p+FfTuHUf+ww== Message-ID: <073e5e2c-7102-4141-b0d7-fa5635f811f5@kernel.org> Date: Tue, 12 May 2026 11:31:22 +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 1/1] mm: batch page copies in folio_copy() and folio_mc_copy() To: Shivank Garg , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org Cc: Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Ankur Arora , Bharata B Rao , Hrushikesh Salunke , David Rientjes References: <20260427142036.111940-2-shivankg@amd.com> <20260427142036.111940-4-shivankg@amd.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: <20260427142036.111940-4-shivankg@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 4/27/26 16:20, Shivank Garg wrote: > Rewrite folio_copy() and folio_mc_copy() as thin wrappers around new > batched helpers copy_highpages() and copy_mc_highpages(). > > The current implementations iterate copy_highpage() (or its #MC-aware > variant) per 4 KB page. For a single 2 MB folio that loop runs 512 > times and pays, per page: > > - kmap_local_page() / kunmap_local() > - cond_resched() > - one invocation of the architecture copy_page()/memcpy() primitive > > The new helpers issue a single copy_mc_to_kernel()/memcpy() over > the whole contiguous range when CONFIG_HIGHMEM is off and no > architecture overrides (__HAVE_ARCH_COPY_HIGHPAGE) copy_highpage(). > HIGHMEM and arch overrides keep the existing per-page path. > > Tested on dual-socket AMD EPYC 9655 (Zen 5) with a CXL.mem node. > In-kernel folio_mc_copy() microbenchmark on 2 MB folios, source > evicted from cache before each iteration and measured throughput: > > direction baseline GB/s optimized GB/s speedup > DRAM0 -> DRAM1 18.65 ± 1.37 38.03 ± 3.21 2.04x > DRAM0 -> CXL 25.46 ± 2.89 39.29 ± 1.17 1.54x > CXL -> DRAM0 20.61 ± 3.95 35.07 ± 0.62 1.70x > > End-to-end move_pages(2) throughput on anonymous 2 MB mTHP folios, > 1 GB migrated per run: > > direction baseline GB/s optimized GB/s speedup > DRAM0 -> DRAM1 7.20 ± 0.03 8.01 ± 0.02 1.11x > DRAM0 -> CXL 11.12 ± 0.15 13.07 ± 0.03 1.18x > DRAM1 -> DRAM0 7.21 ± 0.02 7.95 ± 0.02 1.10x > CXL -> DRAM0 9.10 ± 0.05 9.49 ± 0.01 1.04x > > On AMD EPYC 7713 (Zen 3 / Milan, REP_GOOD without FSRM/ERMS) the > folio_copy() bulk path regresses because memcpy() falls through to > memcpy_orig (an unrolled movq loop), which is slower than the > per-page copy_page() (microcoded rep movsq) it replaces. Do you know what the reason for that fallback is? Could it be fixed (e.g., when we detect page alignment or sth like that?) -- Cheers, David