Re: [PATCH mm] mm: Bring sparc pte_index() semantics inline with other platforms.

[Arjun Roy <arjunroy@google.com>]

David -

For full context, this is for a patchset I was working on within MM to
reduce spinlock operations for TCP receive zerocopy - which is in and
of itself a bit of a complicated situation since it spans mm and
net-next - but this change specifically was to fix building on sparc
for that patch set.

Stephen (cc'd) suggested that perhaps one route would be to get your
ACK for this patch and have it merged into mm, rather than the sparc
tree.
For that matter, I'm still curious as to the best process for merging
the TCP portion of the patch set - would be happy to hear any ideas
you have. I suggested one possibility may be to delay the TCP portion
till net-next eventually picks up the rest of the changes, and just
change TCP then, but am not sure whether that is the best approach.

Thanks,
-Arjun

On Fri, Feb 21, 2020 at 1:17 PM Arjun Roy <arjunroy.kdev@gmail.com> wrote:
>
> From: Arjun Roy <arjunroy@google.com>
>
> pte_index() on platforms other than sparc return a numerical index.
> On sparc, it returns a pte_t*. This presents an issue for
> vm_insert_pages(), which relies on pte_index() to find the offset for
> a pte within a pmd, for batched inserts.
>
> This patch:
> 1. Modifies pte_index() for sparc to return a numerical index, like
>    other platforms,
> 2. Defines pte_entry() for sparc which returns a pte_t*
>    (as pte_index() used to),
> 3. Converts existing sparc callers for pte_index() to use pte_entry().
>
> Signed-off-by: Arjun Roy <arjunroy@google.com>
>
> ---
>  arch/sparc/include/asm/pgtable_64.h | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
> index 65494c3a420e..851ed0f99159 100644
> --- a/arch/sparc/include/asm/pgtable_64.h
> +++ b/arch/sparc/include/asm/pgtable_64.h
> @@ -907,11 +907,12 @@ static inline unsigned long pud_pfn(pud_t pud)
>          (((address) >> PMD_SHIFT) & (PTRS_PER_PMD-1)))
>
>  /* Find an entry in the third-level page table.. */
> -#define pte_index(dir, address)        \
> -       ((pte_t *) __pmd_page(*(dir)) + \
> -        ((address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)))
> -#define pte_offset_kernel              pte_index
> -#define pte_offset_map                 pte_index
> +#define pte_index(address)     \
> +        ((address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1))
> +#define pte_entry(dir, address)        \
> +       ((pte_t *) __pmd_page(*(dir)) + pte_index(address))
> +#define pte_offset_kernel              pte_entry
> +#define pte_offset_map                 pte_entry
>  #define pte_unmap(pte)                 do { } while (0)
>
>  /* We cannot include <linux/mm_types.h> at this point yet: */
> --
> 2.25.0.265.gbab2e86ba0-goog
>