[PATCH v7 07/11] sparc64: optimized struct page zeroing

From: Pavel Tatashin <redacted>
Date: Mon, 28 Aug 2017 22:02:18 -0400

Add an optimized mm_zero_struct_page(), so struct page's are zeroed without
calling memset(). We do eight to ten regular stores based on the size of
struct page. Compiler optimizes out the conditions of switch() statement.

SPARC-M6 with 15T of memory, single thread performance:

                               BASE            FIX  OPTIMIZED_FIX
        bootmem_init   28.440467985s   2.305674818s   2.305161615s
free_area_init_nodes  202.845901673s 225.343084508s 172.556506560s
                      --------------------------------------------
Total                 231.286369658s 227.648759326s 174.861668175s

BASE:  current linux
FIX:   This patch series without "optimized struct page zeroing"
OPTIMIZED_FIX: This patch series including the current patch.

bootmem_init() is where memory for struct pages is zeroed during
allocation. Note, about two seconds in this function is a fixed time: it
does not increase as memory is increased.

Signed-off-by: Pavel Tatashin <redacted>
Reviewed-by: Steven Sistare <redacted>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Bob Picco <redacted>

You should probably use initializing stores when you are doing 8
stores and we thus know the page struct is cache line aligned.

But other than that:

Acked-by: David S. Miller <davem@davemloft.net>