Hi Pavel.
On Thu, Aug 03, 2017 at 05:23:47PM -0400, Pavel Tatashin wrote:
> Add an optimized mm_zero_struct_page(), so struct page's are zeroed without
> calling memset(). We do eight regular stores, thus avoid cost of membar.
The commit message does no longer reflect the implementation,
and should be updated.
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Reviewed-by: Bob Picco <bob.picco@xxxxxxxxxx>
> ---
> arch/sparc/include/asm/pgtable_64.h | 32 ++++++++++++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
>
> diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
> index 6fbd931f0570..be47537e84c5 100644
> --- a/arch/sparc/include/asm/pgtable_64.h
> +++ b/arch/sparc/include/asm/pgtable_64.h
> @@ -230,6 +230,38 @@ extern unsigned long _PAGE_ALL_SZ_BITS;
> extern struct page *mem_map_zero;
> #define ZERO_PAGE(vaddr) (mem_map_zero)
>
> +/* This macro must be updated when the size of struct page grows above 80
> + * or reduces below 64.
> + * The idea that compiler optimizes out switch() statement, and only
> + * leaves clrx instructions or memset() call.
> + */
> +#define mm_zero_struct_page(pp) do { \
> + unsigned long *_pp = (void *)(pp); \
> + \
> + /* Check that struct page is 8-byte aligned */ \
> + BUILD_BUG_ON(sizeof(struct page) & 7); \
Would also be good to catch if sizeof > 80 so we do not silently
migrate to the suboptimal version (silent at build time).
Can you at build time catch if size is no any of: 64, 72, 80
and simplify the below a little?
Sam
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