From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta1.migadu.com (out-180.mta1.migadu.com [95.215.58.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E75672DFA3B for ; Wed, 24 Sep 2025 11:47:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758714460; cv=none; b=jX70x3WMBCOV08oPrGAhNC7RnaBK4vNZwtLwSmdqeaB4uqxNKXC7awxhN420nMlfWEGZqlCtvfuwgTohzMUedSiZ/r69rFaFUao4CqzwQAq8uaz1j18P/h0u4gjdtXLWQG6PianddqJ4TBshcY9Q2ku3T61g/vioKkEjIdYhhPM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758714460; c=relaxed/simple; bh=Umn7lAXySQdSfHE/td8ThDBVs4E2qFo6My0ycKda0Bc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=O3EGfcBphBNCWjw6RWELRtqz4L2uIk3CwOeNShTJXe8l6IFMmpvBkaNUSCDZXysPvoGc30NDA+h1GoBQbYCO4OXTAbufaS2UpJ2xD+Qp/q76OdIvhmvAPgECSD8F4FAENL4zQ6VXYlsBO+JtxuEa+VmQFifM2BmLvBEyILi0IXk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=qY66QdpD; arc=none smtp.client-ip=95.215.58.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="qY66QdpD" Message-ID: <69621b58-5142-48ea-9dd8-6baed69e50f8@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758714449; 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=PdcuQ8Buyt2j7x4RPegt18kSFyuHpvpqm9DsW5GElrw=; b=qY66QdpDELzY/5yp8cWJGqLqn036vXC519/RCLb15ck8tZjNsuwyKNx9nflHkSV7+DPYdH e9f6ElixZrGIqXGYlkQLkmxtwRjfgnDllGf8+d+tIU2rcJFw9xLfT3SVBuWyphoDIqHiVu fNqjgNIPtDeQSenrm1+ei04ezkjb8No= Date: Wed, 24 Sep 2025 19:47:11 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH mm-new 1/1] mm/khugepaged: abort collapse scan on non-swap entries Content-Language: en-US To: David Hildenbrand Cc: lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, hughd@google.com, ioworker0@gmail.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mpenttil@redhat.com, npache@redhat.com, ryan.roberts@arm.com, ziy@nvidia.com, richard.weiyang@gmail.com, akpm@linux-foundation.org References: <20250924100207.28332-1-lance.yang@linux.dev> <1282de5a-3dce-443d-91d1-111103140973@redhat.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <1282de5a-3dce-443d-91d1-111103140973@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2025/9/24 18:10, David Hildenbrand wrote: > On 24.09.25 12:02, Lance Yang wrote: >> From: Lance Yang >> >> The existing check in hpage_collapse_scan_pmd() is specific to uffd-wp >> markers. Other special markers (e.g., GUARD, POISONED) would not be >> caught >> early, leading to failures deeper in the swap-in logic. >> >> hpage_collapse_scan_pmd() >>   `- collapse_huge_page() >>       `- __collapse_huge_page_swapin() -> fails! >> >> As David suggested[1], this patch skips any such non-swap entries early. >> If a special marker is found, the scan is aborted immediately with the >> SCAN_PTE_NON_PRESENT result, as Lorenzo suggested[2], avoiding wasted >> work. > > Note that I suggested to skip all non-present entries except swap > entries, which includes migration entries, hwpoisoned entries etc. Oops, I completely misunderstood your suggestion :( It should be to handle all special non-present entries (migration, hwpoison, markers), not just a specific type of marker ... How about this version, which handles all non-swap entries as you suggested? diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 7ab2d1a42df3..27f432e7f07c 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1284,7 +1284,23 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR; _pte++, addr += PAGE_SIZE) { pte_t pteval = ptep_get(_pte); - if (is_swap_pte(pteval)) { + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { + ++none_or_zero; + if (!userfaultfd_armed(vma) && + (!cc->is_khugepaged || + none_or_zero <= khugepaged_max_ptes_none)) { + continue; + } else { + result = SCAN_EXCEED_NONE_PTE; + count_vm_event(THP_SCAN_EXCEED_NONE_PTE); + goto out_unmap; + } + } else if (!pte_present(pteval)) { + if (non_swap_entry(pte_to_swp_entry(pteval))) { + result = SCAN_PTE_NON_PRESENT; + goto out_unmap; + } + ++unmapped; if (!cc->is_khugepaged || unmapped <= khugepaged_max_ptes_swap) { @@ -1293,7 +1309,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, * enabled swap entries. Please see * comment below for pte_uffd_wp(). */ - if (pte_swp_uffd_wp_any(pteval)) { + if (pte_swp_uffd_wp(pteval)) { result = SCAN_PTE_UFFD_WP; goto out_unmap; } @@ -1304,18 +1320,6 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, goto out_unmap; } } - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { - ++none_or_zero; - if (!userfaultfd_armed(vma) && - (!cc->is_khugepaged || - none_or_zero <= khugepaged_max_ptes_none)) { - continue; - } else { - result = SCAN_EXCEED_NONE_PTE; - count_vm_event(THP_SCAN_EXCEED_NONE_PTE); - goto out_unmap; - } - } if (pte_uffd_wp(pteval)) { /* * Don't collapse the page if any of the small --- Thanks, Lance