From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8A6D7606A32D for ; Mon, 2 Nov 2026 08:43:36 +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=XT9e/Ixt Received: by kanga.kvack.org (Postfix) id 7A73E6B00EF; Mon, 2 Nov 2026 03:43:35 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7584E6B05B1; Mon, 2 Nov 2026 03:43:35 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 647876B05B4; Mon, 2 Nov 2026 03:43:35 -0500 (EST) 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 2EBD76B00EF for ; Mon, 2 Nov 2026 03:43:35 -0500 (EST) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 8FB37140333 for ; Mon, 2 Nov 2026 08:43:34 +0000 (UTC) X-FDA: 85389540348.01.1A27167 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf14.hostedemail.com (Postfix) with ESMTP id CA909100008 for ; Mon, 2 Nov 2026 08:43:32 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="XT9e/Ixt"; spf=pass (imf14.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793609012; b=Nj7siju8OQZbJ9WXC4KGt/3bmoaOQEOC+vxrv/XE4ebiul3LsBowm7+9vM2KiJ+oJmqFmG LV4cNaf/sfKyyv5zs6/zXWO7tWk9VW9Bf+KR7YM8/DqOhwSRjnFiaZALt2nfp0IqOBH9t0 idLqMWZoJyn8BEUaY3IUJKuAISr50cc= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="XT9e/Ixt"; spf=pass (imf14.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793609012; 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=H8IZTJpEEUQHCCQekZ6Kkx0jDr5Kasg15y/uILRyENE=; b=2dCX2lK5ktI4cX9xZmrs675UPXZKLRnhbiDkkb9TVXnmIyExbTLo7J4E8yxJv8iLM/4mxF uMW4mCpt086j/eIgFtcCNDkxedIZGMeesOcApa99V2VfLR660l2duSXnY97Ht8oP1PFkUx kTLkDoBdJLx4CsuMS4BU/zvWUlIhyN4= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id E8C6D439AD; Mon, 2 Nov 2026 08:43:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6828E1F000C1; Mon, 2 Nov 2026 08:43:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793609011; bh=H8IZTJpEEUQHCCQekZ6Kkx0jDr5Kasg15y/uILRyENE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=XT9e/Ixt2VRKUBN23d6OsOv+YMnoKfPXyhSCtL4boUac9vLUICBrJ0K9uMfnzwn8o 8w6CaciZpkg7HYzLmGTDy0GmvXtDftudG9AZsZ8fpFkWcM+2wEdatcb84CTCGUfnpZ cs+D/UPYJNOIXMDIP+HKhmaFQg4BmBYB3IwVszRH6lTKMRGoAlAougpHDlVDG4aJgj oI/bJZ7obLwyLwTT4H5TkQ0hyaQyAYbKcqCk+bfUpq4OlUR1Ku2FM5csVvyStFzPrG T3vuoQwcx6zUl7zjks4G2gn+tvaoLeTq7lqf92onTtvFLzQraAtlRksghdQAkDXXyY PPcnf7RdagpLQ== Message-ID: Date: Mon, 2 Nov 2026 09:43:17 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 18/47] mm/khugepaged: check if PTE table is empty in try_collapse_pte_mapped_thp() To: Baolin Wang , Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Muhammad Usama Anjum References: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> <20261031-fixes_core-v3-18-d6437171ecc3@kernel.org> <62268831-f6f3-4666-a32f-a77546b95432@linux.alibaba.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: CA909100008 X-Stat-Signature: 1kghr6y64dxmqn9jikowk7jzgrh5u4yq X-Rspamd-Server: rspam01 X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=4.0.1 X-HE-Tag: 1793609012-983851 X-HE-Meta: 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 3oijCpIB 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/2/26 09:20, Baolin Wang wrote: > > > On 10/31/26 5:39 PM, David Hildenbrand (Arm) wrote: >> The existing code is rather horrible and already resulted in bugs in the >> past: we special-case UFFD inserting anonymous folios by grabbing the PMD >> lock early, but ignore any other markers (guard, poison through uffd) that >> could have been inserted into the page table in the meantime, effectively >> dropping them. >> >> Let's just unify and simplify the locking: try to grab the PMD table >> lock and if that fails, flush the TLB, drop the PTE lock, take PT locks in >> the right order and check if the page table is still empty. >> >> We still perform the heavy lifting (zapping the folio ptes) under PTE table >> lock only. >> >> Include for now, as x86's flush_tlb_range() macro >> depends on hugetlb helpers. This dependency needs a separate cleanup. >> >> Both issues this fixes are rather corner cases. Let's not CC stable for >> now. >> >> Fixes: f807123d578d ("mm: allow guard regions in file-backed and read-only >> mappings") >> Fixes: 1043173eb5eb ("mm/khugepaged: collapse_pte_mapped_thp() with >> mmap_read_lock()") >> Tested-by: Gregory Price (Meta) >> Reviewed-by: Gregory Price (Meta) >> Tested-by: Muhammad Usama Anjum >> Signed-off-by: David Hildenbrand (Arm) >> --- >>   mm/khugepaged.c | 64 ++++++++++++++++++++++++++++----------------------------- >>   1 file changed, 31 insertions(+), 33 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index ce794d9760a87..ad07c8caa3bd9 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -10,6 +10,7 @@ >>   #include >>   #include >>   #include >> +#include >>   #include >>   #include >>   #include >> @@ -1832,6 +1833,17 @@ static enum scan_result set_huge_pmd(struct >> vm_area_struct *vma, unsigned long a >>       return SCAN_SUCCEED; >>   } >>   +static bool pte_table_empty(pte_t *pte) >> +{ >> +    int i; >> + >> +    for (i = 0; i < HPAGE_PMD_NR; i++, pte++) { > > Using PTRS_PER_PTE to iterate PTEs seems more straightforward? Otherwise LGTM. The difference currently shouldn't matter. I'll probably leave it as is for no such that I can move forward with upstreaming them soonish (having the code as is in -next for a couple of days). But this might be reasonable to clean up alter, thanks! -- Cheers, David