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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: dgeb98789a7jurfznmmr1u8k34gt8c19 X-Rspamd-Queue-Id: EE4CEA0006 X-Rspamd-Server: rspam09 X-HE-Tag: 1760454743-210633 X-HE-Meta: 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 Tf97/Jxj 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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 14.10.25 17:01, Lance Yang wrote: > > > On 2025/10/14 22:39, Lorenzo Stoakes wrote: >> On Tue, Oct 14, 2025 at 10:26:20PM +0800, Lance Yang wrote: >>> >>> >>> On 2025/10/14 19:08, Lorenzo Stoakes wrote: >>>> On Wed, Oct 08, 2025 at 11:26:57AM +0800, Lance Yang wrote: >>>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>>>> index abe54f0043c7..bec3e268dc76 100644 >>>>> --- a/mm/khugepaged.c >>>>> +++ b/mm/khugepaged.c >>>>> @@ -1020,6 +1020,11 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm, >>>>> if (!is_swap_pte(vmf.orig_pte)) >>>>> continue; >>>>> >>>>> + if (non_swap_entry(pte_to_swp_entry(vmf.orig_pte))) { >>>>> + result = SCAN_PTE_NON_PRESENT; >>>>> + goto out; >>>>> + } >>>> >>>> OK seems in line with what we were discussing before... >>> >>> Yep. That's the idea :) >>> >>>> >>>>> + >>>>> vmf.pte = pte; >>>>> vmf.ptl = ptl; >>>>> ret = do_swap_page(&vmf); >>>>> @@ -1281,7 +1286,23 @@ 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))) { >>>> >>> >>> Thanks for pointing that out! >> >> You've deleted what I've said here and also not indicated whether you'll do what >> I asked :) >> >> Please be clearer... > > Oh, I didn't delete your comment at all ... It's just below ... > >> >>>>>> Hm but can't this be pte_protnone() at this stage (or something > else)? And then <-- Here! >>> >>> Yeah. The funny thing is, a protnone pte cannot actually get here, IIUC. >>> >>> ``` >>> static inline int pte_protnone(pte_t pte) >>> { >>> return (pte_flags(pte) & (_PAGE_PROTNONE | _PAGE_PRESENT)) >>> == _PAGE_PROTNONE; >>> } >>> >>> static inline int pte_present(pte_t a) >>> { >>> return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE); >>> } >>> ``` >>> >>> On x86, pte_present() returns true for a protnone pte. And I'd assume >>> other archs behave similarly ... >> >> This was one example, we may make changes in the future that result in entries >> that are non-present but also non-swap. >> >> I don't see the point in eliminating this check based on an implicit, open-coded >> assumption that this can never be the case, this is just asking for trouble. >> >>> >>>> we're just assuming pte_to_swp_entry() is operating on a swap entry when it in >>>> fact might not be? >>>> >>>> Couldn't we end up with false positives here? >>> >>> Emm, I think we're good here and the code is doing the right thing. >> >> I mean sorry but just - NO - to doing swap operations based on open-coded checks >> that you implicitly feel must imply a swap entry. >> >> This makes the code a lot more confusing, it opens us up to accidentally >> breaking things in future and has little to no benefit, I don't see why we're >> doing it. >> >> I don't think every little 'aha X must imply Y so just eliminate Z' idea need be >> implemented, this feels like a sort of 'mathematical reduction of code ignoring >> all other factors'. > > Understood. Changing !pte_present() to is_swap_pte() will resolve all your > concerns, right? > > ``` > if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > [...] > } else if (is_swap_pte(pteval)) { <-- Here > if (non_swap_entry(pte_to_swp_entry(pteval))) { > [...] > } > [...]} Can we please take a step back and make sure we are not starting to do stuff differently than elswehere in the kernel, please? -- Cheers David / dhildenb