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From: Lance Yang In-Reply-To: <20251010132950.yx6bmvub3a46gcl3@master> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: E2CC080015 X-Rspamd-Server: rspam02 X-Stat-Signature: exuf554q4b76sqrrye65s9zjejeych4c X-HE-Tag: 1760104551-973781 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 2025/10/10 21:29, Wei Yang wrote: > On Wed, Oct 08, 2025 at 12:37:48PM +0800, Lance Yang wrote: >> From: Lance Yang >> >> As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd() >> and __collapse_huge_page_isolate() was almost duplicated. >> >> This patch cleans things up by moving all the common PTE checking logic >> into a new shared helper, thp_collapse_check_pte(). While at it, we use >> vm_normal_folio() instead of vm_normal_page(). >> >> Suggested-by: David Hildenbrand >> Suggested-by: Dev Jain >> Signed-off-by: Lance Yang >> --- >> mm/khugepaged.c | 243 ++++++++++++++++++++++++++---------------------- >> 1 file changed, 130 insertions(+), 113 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index b5c0295c3414..7116caae1fa4 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -61,6 +61,12 @@ enum scan_result { >> SCAN_PAGE_FILLED, >> }; >> >> +enum pte_check_result { >> + PTE_CHECK_SUCCEED, >> + PTE_CHECK_CONTINUE, >> + PTE_CHECK_FAIL, >> +}; >> + >> #define CREATE_TRACE_POINTS >> #include >> >> @@ -533,62 +539,139 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte, >> } >> } >> >> +/* >> + * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse >> + * @pte: The PTE to check >> + * @vma: The VMA the PTE belongs to >> + * @addr: The virtual address corresponding to this PTE >> + * @foliop: On success, used to return a pointer to the folio >> + * Must be non-NULL >> + * @none_or_zero: Counter for none/zero PTEs. Must be non-NULL >> + * @unmapped: Counter for swap PTEs. Can be NULL if not scanning swaps >> + * @shared: Counter for shared pages. Must be non-NULL >> + * @scan_result: Used to return the failure reason (SCAN_*) on a >> + * PTE_CHECK_FAIL return. Must be non-NULL >> + * @cc: Collapse control settings >> + * >> + * Returns: >> + * PTE_CHECK_SUCCEED - PTE is suitable, proceed with further checks >> + * PTE_CHECK_CONTINUE - Skip this PTE and continue scanning >> + * PTE_CHECK_FAIL - Abort collapse scan >> + */ >> +static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma, >> + unsigned long addr, struct folio **foliop, int *none_or_zero, >> + int *unmapped, int *shared, int *scan_result, >> + struct collapse_control *cc) >> +{ >> + struct folio *folio = NULL; >> + >> + if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) { >> + (*none_or_zero)++; >> + if (!userfaultfd_armed(vma) && >> + (!cc->is_khugepaged || >> + *none_or_zero <= khugepaged_max_ptes_none)) { >> + return PTE_CHECK_CONTINUE; >> + } else { >> + *scan_result = SCAN_EXCEED_NONE_PTE; >> + count_vm_event(THP_SCAN_EXCEED_NONE_PTE); >> + return PTE_CHECK_FAIL; >> + } >> + } else if (!pte_present(pte)) { >> + if (!unmapped) { >> + *scan_result = SCAN_PTE_NON_PRESENT; >> + return PTE_CHECK_FAIL; >> + } >> + >> + if (non_swap_entry(pte_to_swp_entry(pte))) { >> + *scan_result = SCAN_PTE_NON_PRESENT; >> + return PTE_CHECK_FAIL; >> + } >> + >> + (*unmapped)++; >> + if (!cc->is_khugepaged || >> + *unmapped <= khugepaged_max_ptes_swap) { >> + /* >> + * Always be strict with uffd-wp enabled swap >> + * entries. Please see comment below for >> + * pte_uffd_wp(). >> + */ >> + if (pte_swp_uffd_wp(pte)) { >> + *scan_result = SCAN_PTE_UFFD_WP; >> + return PTE_CHECK_FAIL; >> + } >> + return PTE_CHECK_CONTINUE; >> + } else { >> + *scan_result = SCAN_EXCEED_SWAP_PTE; >> + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE); >> + return PTE_CHECK_FAIL; >> + } >> + } else if (pte_uffd_wp(pte)) { >> + /* >> + * Don't collapse the page if any of the small PTEs are >> + * armed with uffd write protection. Here we can also mark >> + * the new huge pmd as write protected if any of the small >> + * ones is marked but that could bring unknown userfault >> + * messages that falls outside of the registered range. >> + * So, just be simple. >> + */ >> + *scan_result = SCAN_PTE_UFFD_WP; >> + return PTE_CHECK_FAIL; >> + } >> + >> + folio = vm_normal_folio(vma, addr, pte); >> + if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) { >> + *scan_result = SCAN_PAGE_NULL; >> + return PTE_CHECK_FAIL; >> + } >> + >> + if (!folio_test_anon(folio)) { >> + VM_WARN_ON_FOLIO(true, folio); >> + *scan_result = SCAN_PAGE_ANON; >> + return PTE_CHECK_FAIL; >> + } >> + >> + /* >> + * We treat a single page as shared if any part of the THP >> + * is shared. >> + */ >> + if (folio_maybe_mapped_shared(folio)) { >> + (*shared)++; >> + if (cc->is_khugepaged && *shared > khugepaged_max_ptes_shared) { >> + *scan_result = SCAN_EXCEED_SHARED_PTE; >> + count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); >> + return PTE_CHECK_FAIL; >> + } >> + } >> + >> + *foliop = folio; >> + >> + return PTE_CHECK_SUCCEED; >> +} >> + > > This one looks much better. > > While my personal feeling is this is not a complete work to merge the scanning > logic. We still have folio_expected_ref_count() and pte_young() check present > both in __collapse_huge_page_isolate() and huge_collapse_scan_pmd(). Yep, good catch! There's definitely more that can be done. For now, let's keep this patch as-is to avoid making it too complex. Let's get this one in first, and then we can work on the next step :)