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[2003:d8:2f05:e100:526f:9b8:bd2a:2997]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fb72fb017sm17722543f8f.3.2025.09.29.03.29.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Sep 2025 03:29:35 -0700 (PDT) Message-ID: Date: Mon, 29 Sep 2025 12:29:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new 1/1] mm/khugepaged: abort collapse scan on non-swap entries To: Lance Yang 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> <69621b58-5142-48ea-9dd8-6baed69e50f8@linux.dev> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3903D4000F X-Stat-Signature: nh7fsbxetggnzneyo9hiy61ggpf8afhd X-Rspam-User: X-HE-Tag: 1759141780-748535 X-HE-Meta: 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 qW3exB2H jxtwmFL39J9U7MNWWz23W6XYdpVkZrtnny4B0J0qrTmbDavKRLjJtY4BepsmrKggPw+rcDe+Nz8YfPy0PkmHYvT6/wwX1LoWeKFQmR15LKCIfrzfi/0cYysFxsG/GdA9hXIosj4aTcLcFVSt4s+G5Z5f8l/bEAipjNcU0rQS2wI2QCE8gJoEKt++fjDN8mBq52JfyKqR8o9nL/tBjmrN1PYJVvTfhLvG2CutpkZPZaf6ucF/5pKuQUioAMEmW5HFnRYai1vLOMNnycbvuey84wWWbstNLF5YNwMzmie2c/32Xzid5dMOB3gkPnC6oNP6F97x9woBiH1bl+UVrK4iazb70H2J8zdiW2tmrJCvV7J9k/5HVIoJSODBAZRxZ9gNqCa9QCok0f8RF7yRg/uSxp4itC8qLP/Y+L9v3g7lD6Mk6OjKSYMhAQbggB47ls9TpHfa/vpzwPotF/479E6DEHSbMCKGDtBNtTCthfrMoG8IIv3s= 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 24.09.25 13:47, Lance Yang wrote: > > > 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)) { From a quick glimpse, this should work. And as raised, we might be able to unify later the scanning with the almost-duplicated code when we do the second scan. -- Cheers David / dhildenb