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SubjectRe: [PATCH v7 3/3] mm/madvise: optimize lazyfreeing with mTHP in madvise_free
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>> +			nr = madvise_folio_pte_batch(addr, end, folio, pte,
>> + ptent, &any_young, &any_dirty);
>> +
>> + if (nr < folio_nr_pages(folio)) {
>> + if (folio_likely_mapped_shared(folio))
>> + continue;
>> +
>> + arch_leave_lazy_mmu_mode();
>> + if (madvise_pte_split_folio(mm, pmd, addr,
>> + folio, &start_pte, &ptl))
>> + nr = 0;
>> + if (!start_pte)
>> + break;
>> + pte = start_pte;
>> + arch_enter_lazy_mmu_mode();
>> + continue;
>> + }
>> +
>> + if (any_young)
>> + ptent = pte_mkyoung(ptent);
>> + if (any_dirty)
>> + ptent = pte_mkdirty(ptent);
>> }
>>
>> + if (folio_mapcount(folio) != folio_nr_pages(folio))
>> + continue;
>
> Why is this here? I thought we had previously concluded to only do this test
> inside the below if statement (where you have it duplicated).

I stumbled over these same while reviewing. It's not exactly duplicate,
because it's unreliable without the folio lock. It looks more like an
best-effort early check.

But then, we also add it to cases where we previously wouldn't check the
mapcount at all: when the folio was added to the swapcache or is already
dirty.

In that case, we would even see a change for order-0 folios with that
new check.

--
Cheers,

David / dhildenb


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