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 828FAC61DD3 for ; Mon, 31 Aug 2026 11:16:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7D62F6B0092; Mon, 31 Aug 2026 07:16:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7AEBC6B0095; Mon, 31 Aug 2026 07:16:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6EC126B0096; Mon, 31 Aug 2026 07:16:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 4D8F76B0092 for ; Mon, 31 Aug 2026 07:16:52 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id D1EE21C201E for ; Mon, 31 Aug 2026 11:16:51 +0000 (UTC) X-FDA: 85161312222.21.A779A72 Received: from mta0.migadu.com (out-143.mta0.migadu.com [91.218.175.143]) by imf17.hostedemail.com (Postfix) with ESMTP id 6492C40006 for ; Mon, 31 Aug 2026 11:16:49 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=Bd1eZyep; spf=pass (imf17.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.143 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788175010; b=Qo2gzm4z25Pj9EpFLv5akYexWLPR0doEEoi7r83o1SczbAkChx2D63fDigWIqQx7NjWcfX jq60U1IBQmyYEwI46LPjvDFM5h6do6PcJYQ7WuBztFM1ixDEGis8UgTm4bfSBmhSkJmmBX haExRfkuGYEKUnbNxO+jYy/R5fAIZhg= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=Bd1eZyep; spf=pass (imf17.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.143 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788175010; 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=VwdftaVIZmlh3CDWUjMMFKtdPpiSiH6htcM146k0hFw=; b=v2DGdS8lwpWxy3t8cZgBpBIkAvb1JhOD+dlkqbdybSzf+EPSfXvfdekCRE36/wy9JXHjzQ qbYc1qLbA6ObnlRvjLIwVupyuG1PcOujqTke57p5oJOPyIMP4mLjyI4dHvDcHicaJN0ONG jcq4L8+D+9liJXsZL7SQU5kW2CFz5yM= X-Envelope-To: linux-mm@kvack.org DKIM-Signature: a=rsa-sha256; bh=YWlxGEd+q0psBfApITqKzWdA2Uw4k5OebAGh84O7dtE=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788175008; v=1; x=1788779808; b=Bd1eZyepJx6PRVcMTMWIlRP0f7pJy/cLLz2ciTdASJ1IBA23DNGpHDlL67xdx1J8o32VGXwt c7yOurJw6GgP/WLL7pQoUT+IVX3mddS9HpZUaXfRb85/5pIHEjeMqSff0bYZGZHMbvYAgNbR1LM a51mhcOaFR68btTKtJUR+iD4= X-Envelope-To: linux-mm@kvack.org Received: by smtp.migadu.com with ESMTPS id 5bea7a6055a809e8; Mon, 31 Aug 2026 11:16:47 +0000 X-Mizu-Trace-ID: 5bea7a6055a809e8 X-Migadu-Flow: FLOW_OUT Message-ID: <249e0c30-bdd2-4dec-8c21-57cc4c2dd617@linux.dev> Date: Mon, 31 Aug 2026 19:16:39 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm/huge_memory: do not touch frozen folios in deferred_split_isolate() Content-Language: en-US To: Kiryl Shutsemau Cc: ziy@nvidia.com, kasong@tencent.com, hannes@cmpxchg.org, david@kernel.org, hughd@google.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, liam@infradead.org, usama.arif@linux.dev, nico.pache@linux.dev, dev.jain@arm.com, ryan.roberts@arm.com, balbirs@nvidia.com, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, ljs@kernel.org References: <20260831091514.1879786-1-kirill@shutemov.name> <20260831091514.1879786-2-kirill@shutemov.name> From: Lance Yang In-Reply-To: <20260831091514.1879786-2-kirill@shutemov.name> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6492C40006 X-Stat-Signature: m73e7r1zqrs51kmf67rjbb1ppedxa3ds X-Rspam-User: X-HE-Tag: 1788175009-782502 X-HE-Meta: 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 dmM8DpuV T1WVZdpGkOh6uAQTC1K717ns6pzzsiiVMC/yUUupRLjL/LYYIPq23/lyGuFl84cyUBLJvUrkj/PzkG/uii/XGP4oCELzlFd2m3LYGAlNEkZar1uP25twBcFAQ7SN2CPcNWgDRZGxZ4CWKDUuPmmbRYwh5WmkcgALeoT63In3U6SabMf4guzIKkIlC9pvDdPwTujvySFTUEbUUZn2ITfLTCZoFWZoCCnMguPQn5z1piEzB8PR/eDYG6oq6Cp/LndRruOHs77dVTojOz4n0dmbevM+BP1yqqKevM8wgVpLvtEK10xsV12ujRd12R1xLNZSCmuc3B6FH3G5BGJOVCdJTcHy9Px5nXeTZ6PTghKd2VS2rUxOP0wAsHPSNXSIIgKuK9iVXxpC7rQebTSXDp3g/ookaRD9njJOzB0AOIOadqqOhnKI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/8/31 17:15, 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: > > 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(). > > Nothing is lost by skipping. Everything that frees a queued folio > unqueues it first, and folio_unqueue_deferred_split() clears > PG_partially_mapped and brings MTHP_STAT_NR_ANON_PARTIALLY_MAPPED down > on the way: > > __folio_put(), folios_put_refs() mm/folio.c > __folio_migrate_mapping() mm/migrate.c > shrink_folio_list() mm/vmscan.c > > __folio_freeze_and_split_unmapped() does the same by hand, under the > list_lru lock it holds across the freeze. A freeze that ends in > folio_ref_unfreeze() leaves a folio that is still partially mapped and > still belongs on the queue. > > Fixes: 8422acdc97ed ("mm: introduce a pageflag for partially mapped folios") > Reported-by: Lance Yang > Closes: https://lore.kernel.org/all/20260824131224.73344-1-lance.yang@linux.dev/ > Assisted-by: Claude-Code:claude-opus-5 > Signed-off-by: Kiryl Shutsemau (Meta) > Reviewed-by: Zi Yan > Reviewed-by: Johannes Weiner > --- LGTM. Reviewed-by: Lance Yang