On Mon, Feb 17, 2025 at 07:08:28PM +0000, Matthew Wilcox (Oracle) wrote:
> If the first access to a folio is a read that is then followed by a
> write, we can save a page fault. s390 implemented this in their
> mk_pte() in commit abf09bed3cce ("s390/mm: implement software dirty
> bits"), but other architectures can also benefit from this.
>
> Signed-off-by: Matthew Wilcox (Oracle) <wi...@infradead.org>
> ---
> arch/s390/include/asm/pgtable.h | 7 +------
> mm/memory.c | 2 ++
> 2 files changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index 3ca5af4cfe43..3ee495b5171e 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -1451,12 +1451,7 @@ static inline pte_t mk_pte_phys(unsigned long
> physpage, pgprot_t pgprot)
>
> static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
> {
> - unsigned long physpage = page_to_phys(page);
> - pte_t __pte = mk_pte_phys(physpage, pgprot);
> -
> - if (pte_write(__pte) && PageDirty(page))
> - __pte = pte_mkdirty(__pte);
> - return __pte;
> + return mk_pte_phys(page_to_phys(page), pgprot);
> }
>
> #define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
> diff --git a/mm/memory.c b/mm/memory.c
> index 539c0f7c6d54..4330560eee55 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5124,6 +5124,8 @@ void set_pte_range(struct vm_fault *vmf, struct folio
> *folio,
>
> if (write)
> entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> + else if (pte_write(entry) && folio_test_dirty(folio))
> + entry = pte_mkdirty(entry);
> if (unlikely(vmf_orig_pte_uffd_wp(vmf)))
> entry = pte_mkuffd_wp(entry);
> /* copy-on-write page */
Reviewed-by: Alexander Gordeev <agord...@linux.ibm.com>
Thanks!
