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From: Lance Yang 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> <69621b58-5142-48ea-9dd8-6baed69e50f8@linux.dev> In-Reply-To: <69621b58-5142-48ea-9dd8-6baed69e50f8@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: C6785180015 X-Stat-Signature: rxtb1a6qn6zsspn631a8frum4a1c3479 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1759140624-443921 X-HE-Meta: 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 /POrhjoX /7ZpoNK1ct+YE3KqkWx7v7I9F1OpvZnZ9m1CifhYYRnlfv8KHrsu8SLXKE67g2spbVj1ysss8mWN/Yq80tKvrbfIIklXMyHqP+a+sGZgpl8Gzn+xV0TDoTtTzuUnEwmHbLcEZMm93yJkN4qZRb70tE55WMxuzBkHntTe5G0XGMLR88i7Cage+QaCwrdzssIfYXb5ST1PCi0jE2cgRvWsxbmJTSFkoT4T7u4UBZiGAxrYR7u8QWV0lL5Nelq35hyLtNLHUFYPVar441Y19YwyOr4Cp9tGFjzzB+HjgO4qvkmVl8DM1Dz28wG+2BSxZD8ulQ3JIDVq+rnfCWAIAAZM5/03T/Q== 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 2025/9/24 19:47, 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? @David Gently ping ... > > 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