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 BE3F7CAC597 for ; Mon, 15 Sep 2025 14:42:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 22C218E0011; Mon, 15 Sep 2025 10:42:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1DCDB8E0002; Mon, 15 Sep 2025 10:42:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0CB838E0011; Mon, 15 Sep 2025 10:42:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id E98648E0002 for ; Mon, 15 Sep 2025 10:42:13 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 8C78FC06A9 for ; Mon, 15 Sep 2025 14:42:13 +0000 (UTC) X-FDA: 83891749746.17.4FBFD30 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) by imf12.hostedemail.com (Postfix) with ESMTP id 6E91A4000C for ; Mon, 15 Sep 2025 14:42:11 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=m8NJI9pn; spf=pass (imf12.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.187 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=1757947331; 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=otD0lF88c/W1mhXnZZlmqwcx36asc6J+ruH2BHy82vs=; b=Ny4FnwecABwyvPGZVLd23vbnzF/Pdu7WVH7XXJWtJbwn3UtNefx7kgkSbPn9Kz5jpDr0tt 5OmWLbqUW2vHs0LfHe74SJPqvg/IGgTiQEMmkqJMIgRQu0oBMVgiZZ7rhfA3x9WWEWZF3W HE7WWnESia7p+Jzvex6EO3kdi3ITarg= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1757947331; a=rsa-sha256; cv=none; b=kXMwPawAXyQxuBWppIWQWPVRoRhU0UKl6T48+QyjpIkdE21G7jvMR42EGPs1j774npNBX6 DtF2L6UpP2c1y2V2cQv6yW6vyjjBoZJUbjb1kg63YKJVTePOLqQmV/TOjsAGjPSvYyg64K 6uk9+Seahvx8tQpI2+QCgEVZk+duBzM= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=m8NJI9pn; spf=pass (imf12.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.187 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev Message-ID: <121a0947-88cd-4515-bf14-a2af9b69eb0b@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1757947329; 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=otD0lF88c/W1mhXnZZlmqwcx36asc6J+ruH2BHy82vs=; b=m8NJI9pn7LA1CV/E/15NfiRNHl0491YASPDwDn4YMfZP3tGltyzJLFHg+HiEf4XsPtEI1s h0OVkE2EOubpGiDYXx9Ycwl2n+i0QGGB2Bw2l++MvS+vszzPFGSj1ni4Q7I1hioL12BmpY X88TdsxVe7494tG2OsZwjvuzm/deTls= Date: Mon, 15 Sep 2025 22:42:00 +0800 MIME-Version: 1.0 Subject: Re: [PATCH mm-new 3/3] mm/khugepaged: abort collapse scan on guard PTEs Content-Language: en-US To: Lorenzo Stoakes Cc: akpm@linux-foundation.org, david@redhat.com, ziy@nvidia.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, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20250914143547.27687-1-lance.yang@linux.dev> <20250914143547.27687-4-lance.yang@linux.dev> <59519b0f-af14-4486-9aca-4e721842d45b@lucifer.local> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <59519b0f-af14-4486-9aca-4e721842d45b@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: uo9ew67mi4qzdrgf6r6xm8hwk1fc6usr X-Rspam-User: X-Rspamd-Queue-Id: 6E91A4000C X-Rspamd-Server: rspam10 X-HE-Tag: 1757947331-171876 X-HE-Meta: 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 JAbsEJih 1HGxAcARodVDa92gjpy33CsyYE0VdnzvADwzlPu3QRoeM94dkPsbZjuePR7knROIQbR2wZkMZSe/at2HoZd6hL9Rz6IXIA4NgLIh4jDYJeDWTf6eFNHviiiXC6wBIpHTmhAWDQM0Z8EX0DUz61psBbSI+etwW0Z17HkMp3NED8zwYiR/6uOULB9ymKQMfXH/Sw8Kgf07faSXvKlO09zh/VFvoehQ2mOFiAPe56GrVGW7gEmXCnsYLAkKfLg== 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 2025/9/15 22:08, Lorenzo Stoakes wrote: > On Sun, Sep 14, 2025 at 10:35:47PM +0800, 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 ;) > > No smileys in commit messages please... :) Got it. Apparently, I'm a bit too fond of them ... Will remove it in v2. > >> >> This patch adds a check directly inside the PTE scan loop. If a guard >> marker is found, the scan is aborted immediately with a new SCAN_PTE_GUARD >> status, avoiding wasted work. >> >> Signed-off-by: Lance Yang >> --- >> mm/khugepaged.c | 12 ++++++++++++ >> 1 file changed, 12 insertions(+) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index e54f99bb0b57..910a6f2ec8a9 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -59,6 +59,7 @@ enum scan_result { >> SCAN_STORE_FAILED, >> SCAN_COPY_MC, >> SCAN_PAGE_FILLED, >> + SCAN_PTE_GUARD, > > I wonder if we really need to have it literally called out though, can we just > use: > > SCAN_PTE_NON_PRESENT > > Instead? > > As it is, indeed, non-present :) Makes sense to me. A guard PTE is indeed a special non-present case. So, let's reuse SCAN_PTE_NON_PRESENT for that case ;) Cheers, Lance > >> }; >> >> #define CREATE_TRACE_POINTS >> @@ -1317,6 +1318,16 @@ 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)) { >> + result = SCAN_PTE_GUARD; >> + goto out_unmap; >> + } >> continue; >> } else { >> result = SCAN_EXCEED_SWAP_PTE; >> @@ -2860,6 +2871,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, >> case SCAN_PAGE_COMPOUND: >> case SCAN_PAGE_LRU: >> case SCAN_DEL_PAGE_LRU: >> + case SCAN_PTE_GUARD: >> last_fail = result; >> break; >> default: >> -- >> 2.49.0 >> > > Cheers, Lorenzo