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 D95ED301004 for ; Tue, 2 Jun 2026 12:50:19 +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=1780404620; cv=none; b=ETNr3NfeRazmxyTCtgt4TdFNtk5dTizqeh43AzCp4CsewGatiAr82Ss+EwMdaMM4W/ht7SD+91sXFwVQqG5tC+M8PGKMe33eLttQJYUXlaf6hPcJUNo1sN3CT1vHtF40Rw2v0XKCK+0UVHLnycon6XvrkBedXC0sVTgsdRQ6w2E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780404620; c=relaxed/simple; bh=RDuOWPicSOOyLsALB5bjfGPCSPhYOEcHWu/8j6frATo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=W7J+7ZhEQp83jwHh6miMJ5j1YRd6y7ZW/8w6vhdK6648JXnL1AZFpqpiOvOrosl+08Pz3H5Qh5p3qUE+2vSl1L7qutJmdwgByT4i+JyCTntsZojNLb8Di/srqWhgwX2oBzEw45xDTc6wmNKshuA0EJmGnNsmAq19RYJ1rgfd2Gg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MvTyKwVT; 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="MvTyKwVT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B9C701F00893; Tue, 2 Jun 2026 12:49:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780404619; bh=ZnN2cB0eHRn81UTnQ4Np+H7blIwIT0kEeAcnod2F1qg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=MvTyKwVTzmqplXWDe/K0s7Vq5jYIxP4nqvUrRwm5er2dCYM8ZOu/yPvOpBJq07o1P M7Rh8MRFnfByBNTihb6pz/nvkZNn4sCx1u1K2h9UzonoM/hD5QBkFxBo0fqkz/7iWp 0iwGP8+aIot1KLk90d2xJLq4GXo7aDjVKjFSS4zpDpT5rMgTmoPROZP/TAh8uDXw3m rXMGy0hGpePkHzcqpCOHVAKvKx3S37oIW3YRJR+yLpDenWTONmK8eLjmBjfEBnTOs2 dOTq9DdioBXuxGcCHuielsLKEHqSvjJsQS07QhbaQeZba0KI4gCZnVE3N9r0h6aOpy 9POkdHcV/6rgQ== Message-ID: <47fd307f-267d-49b1-9b62-24a577e48143@kernel.org> Date: Tue, 2 Jun 2026 14:49:46 +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: <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 6/2/26 14:40, Lorenzo Stoakes wrote: > On Tue, Jun 02, 2026 at 01:20:07PM +0200, David Hildenbrand (Arm) wrote: >> On 6/1/26 18:16, Lorenzo Stoakes wrote: >>> >>> 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'm not sure how keeping things in the same tree fixes anything though? I think there is a misunderstanding. I am more thinking in terms of what the TIP tree does, where you can send patches against the integration branch, or against sub-branches that are maintained by sub-maintainers. Terminology starts getting tricky. > > You are just changing the _timing_ of when the conflicts happen at the cost > of making things way more difficult to manage IMO. > > I mean the reductio ad absurdum argument is why isn't all of linux in a > single git tree? :) > > If what you're saying is true it should be without issue? But I think there > would be pretty huge issues... > > And the disadvantage is now we have a bunch of sub-maintainers with write > access to the key mm tree who could make mistakes and break things, > hundreds of topic branches all bundled together, no separation between > anything, and no sense of where anything's at. > > If you're saying submaintainers manage topic branches (this cycle the ONE > tree would have ~400 topic branches right? More if we included versions?) > and then independently merge those into the mm-stable tree I think that's > going to be a disaster in terms of timing/conflicts/etc. > > And you're asking for conflict between submaintainers I think - what if one > person merges his thing that then causes conflict for another etc. etc. > > With separate trees then decisions can be made by the mm core people as to > how to integrate, rather than people unilaterally doing whatever. > > And if you're saying submaintainers won't do that, then essentially you're > saying no submaintainer tree management at all :) which I think is a a bad > idea for a subsystem as busy as mm. > > I think mm is too large now to have everything under one person or a few > people. > > Separate trees implies division of labour, and then the integration tree > can be more of a pure integration tree. Just to clarify: I don't think everybody should have access to everything. I'm currently trying to figure out which options we have. TIP has everything in one tree (with sched/ x86/ ... name space sub-branches). > >> >> 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? > > But what does 'picked up' mean? See above re: concerns. > >> >> This is likely something we'll have to play with to understand what is workable >> and what not. > > Actually, I think we have to decide early - because if you want > submaintainers to test out this sub-tree or sub-branch? Or whatever thing > it's very different asking them to: > > - Create a new tree and do X, Y and Z to sync up with mm-next > > Vs.: > > - Have full write access to mm-next and create branches X, Y and Z and > merge things > Right, let me figure what's actually possible so we can discuss if the sub-branch model even makes sense. >> >>> >>> 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. :) > > :) I mean learning from how others do it is definitely key here. > > Maybe we need to grill Brauner? Yes, already reached out :) -- Cheers, David