From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793974460; b=sN48/StYZO7h72x6B17yY42/k6P02cK4F35Y7Kw/E8pNMLAjHWTdP9SQi7Pek3RFIFQP mXCzbQjHR8SRcXJZiU2ehqG2Z7uJg0Eep18rMvnkJcPeBehia/FmVvyg0uRwUhexxKbp/ JyV20sXXZru8C5V823uhMQMvs20BK2jedfY/n+D7M5DmR1nNGuaX6FkKkWjL6wLRyypm7 MB5fT2p2rXeEPPCcml9Al+MdSEGce0EpPH71IDSQ3oG/UFP2590TYZSzbADDRpPevJeWU fJwb7imQqgyKB4I6UCHgNqsmWXCVLxBrJTkSLKO61ewsoc478+SXqNi3efQy0TLE9fQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793974460; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=9avFlgR2Q13CUtm3xqFDLDSVodrfgmDEXnm1JNjvm6g=; b=bdQf4x1TLgHZ0fMnLIN2OcdMQY38KNczkMeCWweRmEKQAF7B6w51iYHY8H8T1aCXHyim T2g3zCD3aGHjUVi6Q/mn+i72PLoHI2mI347lu1uRi4nQX569u83LVsDYSAoP6jcspQ5M/ aLMJPHhJDqU6sZW65aFeadFDukvhT4bQjlCMHnLbucdy93AJjRaT72rx+gatNEXmQCOOs 9T/KUTbuJcMbvvW3qwTZeH48ev7z4kaSZkm1V6AKKUXwCeJ35VUsz10/MnGvZmPVbTVSN uruV4S2korKQJuxgT9zQflu+Wd5Qaukd+88evXIikU5jXdoTL3y0Uz7QQTeHEhHZPuQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cwTpowhI; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E2DA3606A32D for ; Fri, 6 Nov 2026 14:14:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cwTpowhI Received: by smtp.kernel.org (Postfix) with ESMTPSA id 626BE1F0089F; Fri, 6 Nov 2026 14:14:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793974459; bh=9avFlgR2Q13CUtm3xqFDLDSVodrfgmDEXnm1JNjvm6g=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cwTpowhIo1+jTgCjX5+6IzfjZiGxF7z75LL0/xnttW+7iQLGTgmAPTc48kfKvjqCQ sJToVtfaMXbNtk4b+ZUCr4N8b/bVXHVRBh7Dni7UnQUmDUSjS2O8JKiAtLfx8N4I/0 133tX38UQVvuUMA0WZsk20mXOjubFpm/ihzs6eXLsa165xTXePF1+1Ob+0r7+iz4xv 2+T68PI+L6TTQJxKnXbZDk/SUqCuo0AccG7YniXLvEFZjc7T9w5MVqz6so+y2buEFr ld/14Wj4byupKgsVW65oRpc/Wi/vHfsYFfUw/WlWdXZX27ZTTO0GkdrXwy/7gIexPC x8Qq4EqKO650Q== Message-ID: <2655c45a-8b3e-4684-9c81-11d7b32bf696@kernel.org> Date: Fri, 6 Nov 2026 15:14:11 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm: unqueue deferred split folios outside the lruvec lock To: Andrew Morton , Joanne Koong Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , Qi Zheng , Shakeel Butt , Roman Gushchin , Muchun Song , Zi Yan , Baolin Wang , Ryan Roberts , Barry Song , Usama Arif , Lance Yang , Hugh Dickins References: <20261019230646.3510790-1-joannelkoong@gmail.com> <20261020153648.52636815691868735e9699be@linux-foundation.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: <20261020153648.52636815691868735e9699be@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/21/26 00:36, Andrew Morton wrote: > On Mon, 19 Oct 2026 16:06:46 -0700 Joanne Koong wrote: > >> move_folios_to_lru(), folio_batch_move_lru() and folios_put_refs() call >> folio_unqueue_deferred_split() on folios where the refcount has dropped >> to zero. In these paths, folio_unqueue_deferred_split() is called with >> the lruvec lock often held (move_folios_to_lru() always holds it and >> folio_batch_move_lru()/folios_put_refs() usually hold it for every folio >> in the batch except the first). However, it's not needed to hold the >> lruvec lock. >> >> The lruvec lock protects folio->lru and the reclaim LRU lists whereas >> the deferred split queue lives on folio->_deferred_list in >> deferred_split_lru. The deferred_split_lru is a list_lru with its own >> per-memcg per-node lock. >> >> There are already other existing callers that call >> folio_unqueue_deferred_split() without holding the lruvec lock (eg >> __folio_put(), shrink_folio_list(), __folio_migrate_mapping(), ...). >> >> Add folio_batch_unqueue_deferred_split() and use it in >> move_folios_to_lru(), folio_batch_move_lru(), and folios_put_refs() to >> unqueue each batch of zero-refcount folios from the deferred split list >> after the lruvec lock is released and before >> mem_cgroup_uncharge_folios(). This helps shorten the lruvec lock's >> critical sections, which run with IRQs disabled and are highly >> contended. > > Thanks. > > This is a speedup and not a correctness thing, yes? Let's make it a > 7.4-rcX thing, for the 7.5 merge window. > > I'll park it in the mm-new branch for now. > > If people think the speedup is sufficiently worthwhile then I can add a > cc:stable to it, if clear justification is included in the changelog. I'll pick this up for the next merge window. -- Cheers, David