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From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3D9EE2000E X-Stat-Signature: gskxxk79qbb1ftdp61yk6qyffx3oidc4 X-Rspam-User: X-HE-Tag: 1759142374-891156 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 2025/9/29 18:29, David Hildenbrand wrote: > 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. Sounds good! Let's get this one merged first, and I'll send a follow-up patch to unify the duplicated code as you suggested ;)