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 F1030C61DC4 for ; Thu, 27 Aug 2026 15:56:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EFC9F6B008A; Thu, 27 Aug 2026 11:56:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E871E6B008C; Thu, 27 Aug 2026 11:56:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D28006B0092; Thu, 27 Aug 2026 11:56:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 986C36B008A for ; Thu, 27 Aug 2026 11:56:23 -0400 (EDT) Received: from smtpin27.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 1AAD1804A5 for ; Thu, 27 Aug 2026 15:56:23 +0000 (UTC) X-FDA: 85147501446.27.FDD94F1 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf11.hostedemail.com (Postfix) with ESMTP id 6049940003 for ; Thu, 27 Aug 2026 15:56:21 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=RnBLMIbo; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf11.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 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=1787846181; 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=CFZM7kipCqrjfRTX1FI+8Lmju/ujloZNsIaYeTnQJuk=; b=el2bmTgepxVI8kykMHqNLflZGbY6D4Qg613Yc+0KB74sEA8V3JCA0gtXSMj/NcdZWErimm Os/HJYRZnCw8xFlMVnjV1S06+qdkBs4w10I/CuBsN+Njj3Abmvf01pbVu6BV6/7dePR7Sc /7yLDMhm7RMb+ShP6/tZlRe0GvSQH5E= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=RnBLMIbo; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf11.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1787846181; b=7rkoU8ONlLDJNXYO1RZl1qsMyHXxq4xqGUuEOk38VA4zZyRZ+E3J/nbmAvu8d6yENcgHw9 4nZMBQ7vRiWxbnMC7kDXEGXE/6TyY2+1UpCb7CLO0BjYt0TD17H7F95dziYo2mJfSc0NHa gGCyKkzKEABcQusn7aCXideJdEtkwEg= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id E951A600D2; Thu, 27 Aug 2026 15:56:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8C921F00A3A; Thu, 27 Aug 2026 15:56:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787846180; bh=CFZM7kipCqrjfRTX1FI+8Lmju/ujloZNsIaYeTnQJuk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=RnBLMIboNmK700droCbUYEK/N7su/5Jky1PqrEzotOBgEhcEDvs/aF6DyjsyZqUL8 GPmZCWEbSz+eL9ZubOaprfSPNPTu0UMBEIzCeizzPhq1NFgRP+FGe6lXVciYY0RdHJ dIweo1AO72T2rBqQEZhXFyw7MuhadOnzas4g4US/2Wl4Jmg94z1cup8pHAOrz3bmGr Py6ifCIyvB5+fc4Ea3FtX4+OA0RXwrJ3ytAV/L2q//D0NTfFK+qP0GojGxAM0Me3iS g2Xm2gRl75KQqAYhVgHB5KTjh25bOzS+J+imxOEVGjleGsHSp1T53nvcCwNc+VxkGo NBJAMZmPPAr2g== Message-ID: <81085d1e-90b1-429e-9521-a0c7176c6d0d@kernel.org> Date: Thu, 27 Aug 2026 17:56:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/5] mm/huge_memory: do not touch frozen folios in deferred_split_isolate() To: Zi Yan Cc: Kiryl Shutsemau , akpm@linux-foundation.org, ljs@kernel.org, hannes@cmpxchg.org, usama.arif@linux.dev, lance.yang@linux.dev, hughd@google.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, liam@infradead.org, nico.pache@linux.dev, dev.jain@arm.com, ryan.roberts@arm.com, balbirs@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kiryl Shutsemau (Meta)" References: <20260826162101.1314941-1-kirill@shutemov.name> <20260826162101.1314941-2-kirill@shutemov.name> <50FDE99F-3E71-47B8-BD88-05AD771C4BDF@nvidia.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: <50FDE99F-3E71-47B8-BD88-05AD771C4BDF@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: qt8aum8csh359gyzyw6hddoj8zrbo4un X-Rspamd-Queue-Id: 6049940003 X-HE-Tag: 1787846181-21416 X-HE-Meta: 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 h3siv2mp wHtXY0GcRwB5fxDNOZzl+hQhMZZuT78kEy7LI6HenJNEoi+CiWnsaXw+orlPnYsxlhSHVoynllyoXaxY7DCadGMZwMw/UV7d1cyNcgXED6ZYGh43ZuTDiKvqovT36Et3Li/nHLQe810xrzL1RL0mtyu627ebsIJkk2ekqvCoUIYFUC8PLxnfKVS1bHWE5TMNCyjflNzKuq6TinDzfT8T+4/55vjfTO0AR9Ndw3PVm4i0N6FH0R84imevQOrn6EQtYj2e82j3MIm7KveMFireT0/wt2zPdcCeW0bFzJg9PRagXFdFolxxUugMp5x1w5ZEMhHSHtXcCpWSAAEk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/27/26 17:38, Zi Yan wrote: > On 27 Aug 2026, at 11:23, David Hildenbrand (Arm) wrote: > >> On 8/26/26 18:20, Kiryl Shutsemau wrote: >>> From: "Kiryl Shutsemau (Meta)" >>> >>> deferred_split_isolate() probes each queued folio with folio_try_get(). >>> folio_try_get() failure is treated as a lost race with folio_put(): clear >>> PG_partially_mapped, correct MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, take >>> the folio off the queue. >>> >>> The folio_put() race is the most common case for !folio_try_get(), but >>> it is not the only option. Another scenario is folio_ref_freeze(). >>> >>> A zero refcount in such cases does not mean the folio is going away. It >>> means "don't touch me" and current deferred_split_isolate() doesn't >>> respect it. It can lead to unqueueing folios from the deferred list for >>> no reason: >> >> Yes. >> >>> >>> CPU 0 CPU 1 >>> --------------------------- ------------------------------ >>> freeze a mapped folio deferred_split_scan() >>> folio_ref_freeze() folio_try_get() fails >>> folio_clear_partially_mapped() >>> NR_ANON_PARTIALLY_MAPPED-- >>> folio off the queue >>> give up, put it back >>> folio_ref_unfreeze() >>> >>> The folio is still partially mapped, but it is no longer a split candidate. >>> Nothing queues it again until part of it is unmapped once more. >>> >>> Skip the folio instead: whoever freezes the folio, owns it and owner is >>> responsible for its fate. It also covers the folio_put() case: >>> __folio_put() unqueues the folio via folio_unqueue_deferred_split(). >>> >>> Reported-by: Lance Yang >>> Link: https://lore.kernel.org/all/20260824131224.73344-1-lance.yang@linux.dev/ >> >> Fixes? >> >>> Assisted-by: Claude-Code:claude-opus-5 >>> Signed-off-by: Kiryl Shutsemau (Meta) >>> --- >>> mm/huge_memory.c | 19 ++++--------------- >>> 1 file changed, 4 insertions(+), 15 deletions(-) >>> >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index ced400f72d43..6281ed993243 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -4590,22 +4590,11 @@ static enum lru_status deferred_split_isolate(struct list_head *item, >>> struct folio *folio = container_of(item, struct folio, _deferred_list); >>> struct list_head *freeable = cb_arg; >>> >>> - if (folio_try_get(folio)) { >>> - list_lru_isolate_move(lru, item, freeable); >>> - return LRU_REMOVED; >>> - } >>> + /* Lost race to folio_put() or the folio is under folio_ref_freeze() */ >>> + if (!folio_try_get(folio)) >>> + return LRU_SKIP; >>> >>> - /* >>> - * We lost race with folio_put(). Read folio state before the >>> - * isolate: folio_unqueue_deferred_split() checks list_empty() >>> - * locklessly, so once removed the folio can be freed any time. >>> - */ >>> - if (folio_test_partially_mapped(folio)) { >>> - folio_clear_partially_mapped(folio); >>> - mod_mthp_stat(folio_order(folio), >>> - MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1); >>> - } >>> - list_lru_isolate(lru, item); >>> + list_lru_isolate_move(lru, item, freeable); >>> return LRU_REMOVED; >>> } >>> >> >> Who will clean up the stats that we used to clean up? That should be mentioned >> in the commit log, otherwise it looks like some piece of the puzzle is missing. > > It is kinda implied in the last paragraph in the commit log (copied below), > but I agree that stating it explicitly is better. > > |> Skip the folio instead: whoever freezes the folio, owns it and owner is > |> responsible for its fate. It also covers the folio_put() case: > |> __folio_put() unqueues the folio via folio_unqueue_deferred_split(). yes, I read that but was not convinced by it that all existing freezing code would handle it correctly. So spelling that out more clearly would be best. -- Cheers, David