From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 25513CC6B1D for ; Wed, 14 Oct 2026 09:32:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 12A9C6B0098; Wed, 14 Oct 2026 05:32:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0DBE56B0099; Wed, 14 Oct 2026 05:32:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EE64A6B009B; Wed, 14 Oct 2026 05:32:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id B880D6B0098 for ; Wed, 14 Oct 2026 05:32:01 -0400 (EDT) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 4BCD440481 for ; Wed, 14 Oct 2026 09:32:01 +0000 (UTC) X-FDA: 85320715242.01.D8F6161 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf19.hostedemail.com (Postfix) with ESMTP id 7405A1A0003 for ; Wed, 14 Oct 2026 09:31:59 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=lB5mxCOB; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf19.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1791970319; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=KOYPMVBEu35aikHlzxYIXaSJP48EsXpEC6OYR3pCYEg=; b=F9lAwJCqDcFCUh6/b1ZtRCnqJLjY7vyBYvOLBp/A9Skcev4fyXndSNUmyOf2eUNmaorxil cIo02J9eg0bvZqm5sVFIQdMgi631fdPPYLCw1bYhpCxBWU9+2v4t0krkv3lJV/FR1Zo91A 9IwE8ChinrTq2omCH3X6IUbJfkrrysE= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=lB5mxCOB; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf19.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1791970319; b=jniwwkv0rS2Ie/MTt2yzIWwVo9FwJnu3aD5WcN2ARyy/YsEnycMJegFrQPTGvVf3ADMJlC pb/afbxW36vvTWVlDe48ZWcapJ7Nij+b7SsXBt9JC8TPiIYD+/ViesDQVhCnR9OzwUCMQz jdd7BgVHKoaVBBiNzaePwy9+oc7jUu8= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id AAD9042E54; Wed, 14 Oct 2026 09:31:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C48271F000FF; Wed, 14 Oct 2026 09:31:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791970318; bh=KOYPMVBEu35aikHlzxYIXaSJP48EsXpEC6OYR3pCYEg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=lB5mxCOBEnl0TCJuwrjDEwAL8FhUaw1lLBg49iUFpiAIn+qPof9A8DFu3mkO9jynw Eo2F+N44KPhLO+mhy8+Xh1qUCe8tGv3fOK8bPnACBuCom0WvZVb9oS5bLKDwmjJAfG 4kfrWggA+Y4aAxQKHEEQvFGWb3v3vs7PAoNIhIUchSdRkT8Tgns4DA4enKWRv/r0MN tPslUKfVc9h8gLBmy8/R7DAbuoUhDaK68S+G1NHfsCIJgugyEFA9z+ewdMPjg00LmG fKw49V5n0a5XbIZFYFb6lFDvYD8Mw2qGzguC2MlwkEkfmCles4MOqGTBnUGdr6ejp1 CjLI+iwXCL1Tg== Message-ID: Date: Wed, 14 Oct 2026 11:31:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm: unqueue deferred split folios outside the lruvec lock To: Joanne Koong , Andrew Morton 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: <20261013221307.850803-1-joannelkoong@gmail.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: <20261013221307.850803-1-joannelkoong@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 7405A1A0003 X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: qf6sbfgesuqteks3971ueojp9k9rk4dg X-HE-Tag: 1791970319-72936 X-HE-Meta: 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 EkPG6Xv8 1KJcZcpWYbYKP4iNMUqjOix3KQsVZLrq6cppMPGK8kxFa7MwNqkMJ5K5LsMXIvy5rUck2TAodzj8p6iO1yuzw7Bgl02kOkb6/QpxAgauSJ3cYb30lD7bgt3hIlJR6XHd+rrQ6Au6oJbmHJjhiuKhvncVrHCo0fbvJs32kq9bF2HiBF8SWnhzKQ+SlMFJO41nLpDC26E/XtNEw7Yn6gAB0EIfcDF57VvOt6kd4Y0gY7lRR2m9y8EJkEA8WnLvxjl0yAx79Nck/AhNyizemnBj4OlK8UESlc5d+blQ5 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/14/26 00:13, 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. > > Signed-off-by: Joanne Koong > --- > mm/folio.c | 24 +++++++++++++++++++----- > mm/internal.h | 1 + > mm/vmscan.c | 3 ++- > 3 files changed, 22 insertions(+), 6 deletions(-) > > diff --git a/mm/folio.c b/mm/folio.c > index 35e242b48870..85144078e635 100644 > --- a/mm/folio.c > +++ b/mm/folio.c > @@ -109,6 +109,19 @@ EXPORT_SYMBOL(__folio_put); > > typedef void (*move_fn_t)(struct lruvec *lruvec, struct folio *folio); > > +/* > + * Unqueue a batch of folios from the deferred split queue. This must be > + * called after the folios' refcounts have dropped to zero and before they > + * are uncharged (see comment above __folio_unqueue_deferred_split() for why). > + */ > +void folio_batch_unqueue_deferred_split(struct folio_batch *fbatch) > +{ > + unsigned int i; > + > + for (i = 0; i < folio_batch_count(fbatch); i++) > + folio_unqueue_deferred_split(fbatch->folios[i]); > +} > + > static void lru_add(struct lruvec *lruvec, struct folio *folio) > { > int was_unevictable = folio_test_clear_unevictable(folio); > @@ -177,14 +190,10 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) > * > * We're bypassing normal cleanup. Clear flags that are not > * applicable to dead folios. > - * > - * Since the folio may be part of a huge page, unqueue from > - * deferred split list to avoid a dangling list entry. > */ > if (is_lru_add && folio_ref_freeze(folio, 1)) { > __folio_clear_active(folio); > __folio_clear_unevictable(folio); > - folio_unqueue_deferred_split(folio); > fbatch->folios[i] = NULL; > folio_batch_add(&free_fbatch, folio); > continue; > @@ -201,6 +210,11 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) > > /* Cleanup filtered dead folios. */ > if (is_lru_add) { > + /* > + * Since the folios may be part of a huge page, unqueue them > + * from the deferred split list to avoid a dangling list entry. > + */ In general, this lgtm, thanks. I am confused about this existing comment you are moving. folios being *part of* a huge page? Huh? A folio might represent a huge page, but what does the "part of" thing mean here. Is it simply "Dequeue any large folios" ? -- Cheers, David