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    SubjectRe: [PATCH v3 4/6] mm: introduce arch_do_swap_page_nr() which allows restore metadata for nr pages
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    On 03/05/2024 01:50, Barry Song wrote:
    > From: Barry Song <v-songbaohua@oppo.com>
    >
    > Should do_swap_page() have the capability to directly map a large folio,
    > metadata restoration becomes necessary for a specified number of pages
    > denoted as nr. It's important to highlight that metadata restoration is
    > solely required by the SPARC platform, which, however, does not enable
    > THP_SWAP. Consequently, in the present kernel configuration, there
    > exists no practical scenario where users necessitate the restoration of
    > nr metadata. Platforms implementing THP_SWAP might invoke this function
    > with nr values exceeding 1, subsequent to do_swap_page() successfully
    > mapping an entire large folio. Nonetheless, their arch_do_swap_page_nr()
    > functions remain empty.
    >
    > Cc: Khalid Aziz <khalid.aziz@oracle.com>
    > Cc: "David S. Miller" <davem@davemloft.net>
    > Cc: Andreas Larsson <andreas@gaisler.com>
    > Signed-off-by: Barry Song <v-songbaohua@oppo.com>
    > ---
    > include/linux/pgtable.h | 26 ++++++++++++++++++++------
    > mm/memory.c | 3 ++-
    > 2 files changed, 22 insertions(+), 7 deletions(-)
    >
    > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
    > index 18019f037bae..463e84c3de26 100644
    > --- a/include/linux/pgtable.h
    > +++ b/include/linux/pgtable.h
    > @@ -1084,6 +1084,15 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
    > })
    >
    > #ifndef __HAVE_ARCH_DO_SWAP_PAGE
    > +static inline void arch_do_swap_page_nr(struct mm_struct *mm,
    > + struct vm_area_struct *vma,
    > + unsigned long addr,
    > + pte_t pte, pte_t oldpte,
    > + int nr)
    > +{
    > +
    > +}
    > +#else
    > /*
    > * Some architectures support metadata associated with a page. When a
    > * page is being swapped out, this metadata must be saved so it can be
    > @@ -1092,12 +1101,17 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
    > * page as metadata for the page. arch_do_swap_page() can restore this
    > * metadata when a page is swapped back in.
    > */
    > -static inline void arch_do_swap_page(struct mm_struct *mm,
    > - struct vm_area_struct *vma,
    > - unsigned long addr,
    > - pte_t pte, pte_t oldpte)

    This hook seems to be very similar to arch_swap_restore(), I wonder if it makes
    sense to merge them. Out of scope for this patch series though.


    > -{
    > -
    > +static inline void arch_do_swap_page_nr(struct mm_struct *mm,
    > + struct vm_area_struct *vma,
    > + unsigned long addr,
    > + pte_t pte, pte_t oldpte,
    > + int nr)
    > +{
    > + for (int i = 0; i < nr; i++) {
    > + arch_do_swap_page(vma->vm_mm, vma, addr + i * PAGE_SIZE,
    > + pte_advance_pfn(pte, i),
    > + pte_advance_pfn(oldpte, i));

    It seems a bit odd to create a batched version of this, but not allow arches to
    take advantage. Although I guess your point is that only SPARC implements it and
    on that platform nr will always be 1? So no point right now? So this is just a
    convenience for do_swap_page()? Makes sense.

    Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>

    > + }
    > }
    > #endif
    >
    > diff --git a/mm/memory.c b/mm/memory.c
    > index f033eb3528ba..74cdefd58f5f 100644
    > --- a/mm/memory.c
    > +++ b/mm/memory.c
    > @@ -4266,7 +4266,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
    > VM_BUG_ON(!folio_test_anon(folio) ||
    > (pte_write(pte) && !PageAnonExclusive(page)));
    > set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
    > - arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
    > + arch_do_swap_page_nr(vma->vm_mm, vma, vmf->address,
    > + pte, vmf->orig_pte, 1);
    >
    > folio_unlock(folio);
    > if (folio != swapcache && swapcache) {


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