Re: [PATCH v1 9/9] mm/memory: optimize unmap/zap with PTE-mapped THP

David Hildenbrand
2024-01-30T09:09:00Z

Re-reading the docs myself:

> +#ifndef get_and_clear_full_ptes
> +/**
> + * get_and_clear_full_ptes - Clear PTEs that map consecutive pages of the same
> + * folio, collecting dirty/accessed bits.
> + * @mm: Address space the pages are mapped into.
> + * @addr: Address the first page is mapped at.
> + * @ptep: Page table pointer for the first entry.
> + * @nr: Number of entries to clear.
> + * @full: Whether we are clearing a full mm.
> + *
> + * May be overridden by the architecture; otherwise, implemented as a simple
> + * loop over ptep_get_and_clear_full(), merging dirty/accessed bits into
> + * returned PTE.

"into the"

> + *
> + * Note that PTE bits in the PTE range besides the PFN can differ. For example,
> + * some PTEs might be write-protected.
> + *
> + * Context: The caller holds the page table lock. The PTEs map consecutive
> + * pages that belong to the same folio. The PTEs are all in the same PMD.
> + */
> +static inline pte_t get_and_clear_full_ptes(struct mm_struct *mm,
> + unsigned long addr, pte_t *ptep, unsigned int nr, int full)
> +{
> + pte_t pte, tmp_pte;
> +
> + pte = ptep_get_and_clear_full(mm, addr, ptep, full);
> + while (--nr) {
> + ptep++;
> + addr += PAGE_SIZE;
> + tmp_pte = ptep_get_and_clear_full(mm, addr, ptep, full);
> + if (pte_dirty(tmp_pte))
> + pte = pte_mkdirty(pte);
> + if (pte_young(tmp_pte))
> + pte = pte_mkyoung(pte);
> + }
> + return pte;
> +}
> +#endif
> +
> +#ifndef clear_full_ptes
> +/**
> + * clear_full_ptes - Clear PTEs that map consecutive pages of the same folio.
> + * @mm: Address space the pages are mapped into.
> + * @addr: Address the first page is mapped at.
> + * @ptep: Page table pointer for the first entry.
> + * @nr: Number of entries to clear.
> + * @full: Whether we are clearing a full mm.

Something went missing:

May be overridden by the architecture; otherwise, implemented as a
simple loop over ptep_get_and_clear_full().

--
Cheers,

David / dhildenb