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 6E86E3B2FFD; Wed, 29 Apr 2026 13:04:21 +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=1777467861; cv=none; b=Nn4HmxpxHh0oh2IRKMAM9OMB6e6OZOV/WlA/KTHnkexnmyUT8VcG4Lu1Nirv9CEnOOc5bMwkOWzaeFoChJ0xsJZHVmVQKG+3Kac1gG66/ENcULP1PiDyJbpIxeuPbO++10uWwpq3W5Kp3ZLS2BiXSJTfmIpnBlknWTcSzSUgR/A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777467861; c=relaxed/simple; bh=JKme6JBRrN0TnxQE5dLJVF61YEFWB4vBnH5tddF11mk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aMwrZG8avp7oswaRC6KIlD8+31vWiSInrOYPV0OFNRaugCUyhe/G9fUEsV+3BsXuMOEvw3BcOQDepgXfQ2KnRzFjIL7JLhDvLqmwaSaZSRfPWBg2dNKIHD0aC64vd7RgiU1TLJ5dwU+Zby5gIQTaXLA0j5LHn+WLxZEg4kZkrb8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lOxHuT/f; 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="lOxHuT/f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7C1D1C19425; Wed, 29 Apr 2026 13:04:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777467861; bh=JKme6JBRrN0TnxQE5dLJVF61YEFWB4vBnH5tddF11mk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=lOxHuT/fXVRXH3dDVYllN2Vjqim9hhG3/0+F4jv7LBRnW+GJhaKOOOYxTlsOOTMW6 8JX6BCEYmIS7I5ntuj9FiiQrTsqrYx3Kph1zHoEQPTxqqSbMzMuC7iRnqpiXPVnfE/ 9swRZYEz5Dg0e4wriPHLvhemuTkpGmK0NkGBJCdVk0bcaQ9FTl+4cyyw8IP178Jlys dFjckx9NOzlosfwSeP6EzbFlrv6220ndi9sdE1CM5EoszB+q0ODLkGDmthFko90bhi aMHpSN+uddAbMEfL8XiSB9AM/q4Gel3KvREH/GR3bjtkh7odbYicXzHErF977wji47 cFwVtITuuqoBA== Message-ID: <4ff3d230-d48d-4a9c-aac8-30a7b80c4775@kernel.org> Date: Wed, 29 Apr 2026 15:04:16 +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: [PATCH v6 0/3] mm: Free contiguous order-0 pages efficiently To: Ryan Roberts , Andrew Morton , Johannes Weiner Cc: Muhammad Usama Anjum , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Zi Yan , Uladzislau Rezki , Nick Terrell , David Sterba , Vishal Moola , linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, david.hildenbrand@arm.com References: <20260401101634.2868165-1-usama.anjum@arm.com> <20260429103326.GA1743@cmpxchg.org> <20260429050430.d86f01dbe731edc9fa932add@linux-foundation.org> <9834200a-492c-4705-a2b2-e76cc0ba5392@arm.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: <9834200a-492c-4705-a2b2-e76cc0ba5392@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/29/26 14:31, Ryan Roberts wrote: > On 29/04/2026 13:04, Andrew Morton wrote: >> On Wed, 29 Apr 2026 06:33:26 -0400 Johannes Weiner wrote: >> >>> >>> I think we should revert the original patch. >>> >>> The premise is that we can save some allocator calls by requesting >>> higher orders and splitting them up into singles. This is a frivolous >>> and short-sighted use of a very coveted and expensive resource. > > I'm not sure it's that simple. First off, vmalloc has preferred to allocate high > order pages for quite a while, it's just that the patch you're referring to > makes it try even harder. So reverting the patch doesn't completely revert the > behaviour, it just reduces it. > > Performance benefits because those high order pages are mapped appropriately in > the page table - i.e. 1G PUD, 2M PMD, (or 64K CONTPTE on arm64). So it's not > solely about the number of cycles spent in the allocator; the HW is used more > efficiently. vmalloc only splits to order-0 for the benefit of the caller, > because there are some places that assume they can access each returned struct page. > > And all the order-0 pages of the original high order page are freed at the same > time, so it's not like we are destroying the contiguous resource; it remains > intact for the next user (well, ignoring that some will be freed to the pcpu > list - this series solves that wrinkle). I've heard it argued that this approach > is actually _better_ for conserving contiguous blocks because it's keeping the > lifetime of all the constituent pages bound together and reducing fragmentation. > I've never seen any data though... Right, that's what Willy has said: allocating+freeing larger blocks, especially for unmovable data, reduces fragmentation as a whole. And that theory makes sense for me in the context here. I don't think we want to revert the original patch. -- Cheers, David