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 0734462809 for ; Tue, 2 Jun 2026 11:20:11 +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=1780399213; cv=none; b=E0YBRC6jdIFBk9uT+yX0c1iuu8+nbF1Vrv64FyPKq2iiB0tUVdzGltP7rurfmWBl35s50Tw8ApWbVGGGKIHQ07IeRV2HRF/AIF7KbDQXTuor7WnBPp8DYlkrozOnBfGk8ASnBeg7U1FEIXFZy+AMQHSdR1jv7YHFJemejOnJc8o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780399213; c=relaxed/simple; bh=C1t6lC0i3j/uXxC/sheNUi6jbxwTXmUOEfHU0Wgs10M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZVSwLFZu60oTf/O/JL1vU2G3sXGB1Ak752dBslEa6YHzkolOLMQtZwDD0S7jfrwwn0/vVXkkF77nKun6kOfpwG4IS1W1F75HUfZ47B8U4JMAjAncfyTDShg2npJQUe3NmeQhJfNQEg0TZIBYUi6GZpbVeqVlIIR4f/gS4PQh8Ug= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TZ551xHk; 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="TZ551xHk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 842FC1F00893; Tue, 2 Jun 2026 11:20:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780399211; bh=b0VwkGHBVNeptN+NHtHQcvkdC8qIMdgbt33Tho/gOjU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=TZ551xHkqAQZcxfzW9Q1CknHrlXPAjoTU7OqSOjfBytJMEQA2UEqBd0FhbcrhQOtC cakZ1u4hLn4EIjFCqJQE3wGq65k8coNmN/nXLZz3r/2IcTnqZ0sOHcqJtK0LGSv+1Y lyUg9ssinbndp/wCvOicgtCT2XCuvgrFdDJa4lfT9cxSyoIua9a4Cza/lBcuVrJ4zE /yuRC4PKz2j+KEjc5u4KRUpKbdWfTihZrQ/qv7ISg/qpp/e/XFBCLSekUtyhqI1nCI z/jNE8AYXjRQXQEdU+P87xTPEEfyr01zqOF2RSK4W5ZHe0M+0SY9FPv+XYVQkBLoAl d0Y3NRH7/D6Pw== Message-ID: Date: Tue, 2 Jun 2026 13:20:07 +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: Process (was Re: [PATCH mm-hotfixes-unstable v18 00/14] khugepaged: add mTHP) collapse support To: Lorenzo Stoakes Cc: "Vlastimil Babka (SUSE)" , Nico Pache , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, liam@infradead.org, mhocko@suse.com, rppt@kernel.org, vbabka@suse.cz, willy@infradead.org References: <20260522150009.121603-1-npache@redhat.com> <506fed6b-8954-40fa-8b5e-c8bd8c0d004b@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/1/26 18:16, Lorenzo Stoakes wrote: > On Mon, Jun 01, 2026 at 05:45:30PM +0200, David Hildenbrand (Arm) wrote: >> On 6/1/26 17:41, Lorenzo Stoakes wrote: >>> >>> I think life will be easier with submaintainer separate trees for this honestly >>> :) or it could become a horrible mess in one tree I think. >> >> Requiring contributors to submit stuff targeted at some random trees is madness :) > > Err what? The 'random' tree is the MAINTAINERS entry you are targeting, it's > based on the mm-next stable branch and only diverges in the work that's been > done specific to the subtree, what's crazy exactly? We'll still have plenty of patch sets that touch files cross trees. I don't see the problem of sending stuff against the integration tree from where it can just be cleanly picked up by sub-maintainers (after all, that's where all the subtrees were integrated against)? Or what exactly is the problem with that? This is likely something we'll have to play with to understand what is workable and what not. > > I mean, is there any meaning to separate 'trees' at all if we just have one tree > with topic branches in? > > Or are we going to have several parallel stable branches in one tree, and a > bunch of maintainers with write access stepping on each other's toes? All valid question to which we don't have an answer yet. :) > > That sounds a lot more crazy to me, and I just don't think it's workable. >> >>> >>> I think the simplest is what I suggested in reply to Vlasta, where each >>> submaintainer tree has their own set of changes against mm-next/mm-stable and >>> then we merge each week. >> >> Throw in hotfixes and it already starts being crazy. > > Again I really don't understand this? > > Hotfixes are a completely separate topic for one, I'm talking about ordinary > development, but surely they're simpler aren't they? I mean the interaction: new material that depend on hotfixes. Talking to Michal and Vlastimil last week, there are some ways to make this work based on topic branches (hotfixes being a topic branch IIUC), but I don't understand yet how that works in detail, or how that would scale to subtrees. > > Everything's based on Linus's tree (so no confusion as to which tree), there > shouldn't (hopefully) be a huge amount of them, and submaintainers can just > potentially find a way to send them direct to mm-next anyway? > >> >>> >>> But am open to learning about what other subsystems in the kernel do... >> >> The TIP tree has a pretty elaborate model of dealing with topic branches, and >> don't require things to be sent against specific topic branches. >> >> I'll try to understand that model. > > OK well, interested to hear about that. > > But also we should adapt what others do (which I think is very important to > learn from obviously) against how mm works in practice. > > High review load with many overlapping changes might favour a different approach > to a subsystem that looks different from that. Yeah, but as we said, we discussed, it's all rather complicated and we should move incrementally. -- Cheers, David