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 BC387CAC597 for ; Fri, 19 Sep 2025 02:45:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EB55B28000F; Thu, 18 Sep 2025 22:45:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E8D658E0008; Thu, 18 Sep 2025 22:45:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DC9B528000F; Thu, 18 Sep 2025 22:45:26 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id C9FFF8E0008 for ; Thu, 18 Sep 2025 22:45:26 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 92EA51401C0 for ; Fri, 19 Sep 2025 02:45:26 +0000 (UTC) X-FDA: 83904458652.01.421DEAA Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) by imf06.hostedemail.com (Postfix) with ESMTP id D0822180007 for ; Fri, 19 Sep 2025 02:45:24 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=kkZnUCqS; spf=pass (imf06.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.177 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=1758249925; 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=pEd4CRxp0Qy3iytKkYSUgyoNAPH5uPPdhfTDAiqFt+Q=; b=4bxqlw/uVSWoNWP1z6+OTFPqGnvJfICaaPJEHw0NJAdR4RxdcSY7ocGE0me7GmLD1iEPR7 pss//+Q/GmpS2NRxFzg3n427ZzH8Hw6T97kBXdZ+I9lUubW6+3Vs9AbXp3GY7XDegUNrZi BlcseL46R4aso4nTJyWOlJpIXl6FWJo= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1758249925; a=rsa-sha256; cv=none; b=7kujdij60DcK+IryFDiI77FYUMXBuE/6yEM1yb2/ndSIyOUCssAaP8WzlWrJeDxNC1ljDy QqHNUsQIIZvSyp04FWM2m7XaDNJbS6X5rQCvdoS2azOrozu4cw/GOUmcerVaiyu5tIkTZD gJ/0E6y6toCnh7TjWz5alcBMkVSL95c= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=kkZnUCqS; spf=pass (imf06.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.177 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev Message-ID: <20e0fb73-3476-4b1c-959e-c1af38f8e1a0@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758249922; h=from:from: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; bh=pEd4CRxp0Qy3iytKkYSUgyoNAPH5uPPdhfTDAiqFt+Q=; b=kkZnUCqSVKS2D7eOJzEGuV3v+zGK9iIe7bTiuC/CxNG5peUXCkMg8QwHhrIUCzAA3fPGtj H5dS3iVmdASVXo6qgjNsHY2nKaNPMk5MXf8dk4yu9aiRvB+36+Nq6NC4YvSuED6HU0WwFj /DE5F2zJxguD24b6ukaUVsKcEQQp55k= Date: Fri, 19 Sep 2025 10:44:26 +0800 MIME-Version: 1.0 Subject: Re: [PATCH mm-new v2 2/2] mm/khugepaged: abort collapse scan on guard PTEs Content-Language: en-US To: Zi Yan Cc: akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, ioworker0@gmail.com, kirill@shutemov.name, hughd@google.com, mpenttil@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20250918050431.36855-1-lance.yang@linux.dev> <20250918050431.36855-3-lance.yang@linux.dev> <6BAE5498-D0AB-40F5-85F8-B92A05CA72AD@nvidia.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <6BAE5498-D0AB-40F5-85F8-B92A05CA72AD@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: D0822180007 X-Stat-Signature: sze8smrthnzy1hk8474bksbho83ioyu5 X-Rspam-User: X-HE-Tag: 1758249924-147518 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025/9/19 03:12, Zi Yan wrote: > On 18 Sep 2025, at 1:04, Lance Yang wrote: > >> From: Lance Yang >> >> Guard PTE markers are installed via MADV_GUARD_INSTALL to create >> lightweight guard regions. >> >> Currently, any collapse path (khugepaged or MADV_COLLAPSE) will fail when >> encountering such a range. >> >> MADV_COLLAPSE fails deep inside the collapse logic when trying to swap-in >> the special marker in __collapse_huge_page_swapin(). >> >> hpage_collapse_scan_pmd() >> `- collapse_huge_page() >> `- __collapse_huge_page_swapin() -> fails! >> >> khugepaged's behavior is slightly different due to its max_ptes_swap limit >> (default 64). It won't fail as deep, but it will still needlessly scan up >> to 64 swap entries before bailing out. >> >> IMHO, we can and should detect this much earlier. >> >> This patch adds a check directly inside the PTE scan loop. If a guard >> marker is found, the scan is aborted immediately with SCAN_PTE_NON_PRESENT, >> avoiding wasted work. >> >> Suggested-by: Lorenzo Stoakes >> Signed-off-by: Lance Yang >> --- >> mm/khugepaged.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 9ed1af2b5c38..70ebfc7c1f3e 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -1306,6 +1306,16 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, >> result = SCAN_PTE_UFFD_WP; >> goto out_unmap; >> } >> + /* >> + * Guard PTE markers are installed by >> + * MADV_GUARD_INSTALL. Any collapse path must >> + * not touch them, so abort the scan immediately >> + * if one is found. >> + */ >> + if (is_guard_pte_marker(pteval)) { > > pteval is already is_swap_pte(), would is_guard_swp_entry() be a better > choice here? Save one is_swap_pte() call. Yeah. Good spot! Will do ;) Thanks, Lance > >> + result = SCAN_PTE_NON_PRESENT; >> + goto out_unmap; >> + } >> continue; >> } else { >> result = SCAN_EXCEED_SWAP_PTE; >> -- >> 2.49.0 > > > Best Regards, > Yan, Zi