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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 45495180013 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 7r6x6tzwiosxxn5oncndbemi41ksyqgy X-HE-Tag: 1691072131-191227 X-HE-Meta: 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 Oc7j/cIA zXbGWmPw05m8WUb0NDZOWCvTix3L7oxZy9j8hwSORqjht73NDsih98WW/R49A2KQ5XiihVGFwB4CqnypcXn3gHvJ9uwQXBVTNLzmSHCl8S7Thp+w= 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: On 03/08/2023 15:10, David Hildenbrand wrote: >>> >>> With this patch, you'll might suddenly have mapcount > refcount for a folio, or >>> am I wrong? >> >> Yes you would. Does that break things? >> > > It is problematic whenever you want to check for additional page references that > are not from mappings (i.e., GUP refs/pins or anything else) > > One example lives in KSM code (!compound only): > > page_mapcount(page) + 1 + swapped != page_count(page) > > Another one in compaction code: > > if (!mapping && (folio_ref_count(folio) - 1) > folio_mapcount(folio)) > > And another one in khugepaged (is_refcount_suitable) > > ... and in THP split can_split_folio() (although that can deal with false > positives and false negatives). > > > We want to avoid detecting "no other references" if there *are* other > references. Detecting "there are other references" although there are not is > usually better. > > > Assume you have mapcount > refcount for some time due to concurrent unmapping, > AND some unrelated reference. You would suddenly pass these checks (mapcount == > refcount) and might not detect other references. OK. I'll rework with the 2 loop approach, assuming I can calculate the number of free slots in the mmu_gather ahead of time. > >>> >>>> + >>>> +    for (i = 0; i < nr_pages;) { >>>> +        ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); >>>> +        tlb_remove_tlb_entry(tlb, pte, addr); >>>> +        zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent); >>>> +        full = __tlb_remove_page(tlb, page, 0); >>>> + >>>> +        if (unlikely(page_mapcount(page) < 1)) >>>> +            print_bad_pte(vma, addr, ptent, page); >>> >>> Can we avoid new users of page_mapcount() outside rmap code, please? :) >> >> Sure. This is just trying to replicate the same diagnstics that's done on the >> non-batched path. I'm happy to remove it. > > Spotted it afterwards in the existing code already, so you're effetively not > adding new ones. >