[PATCH] x86/head64: micro optimization: use memset instead of for loop

[Alexander Kuleshov]

This patch simplifies clearing of page table directories, by
the using of the fast memset() from the arch/x86/lib/memset_64.S.
Besides this, we 25 bytes is 25 bytes less than original.

text       data     bss              dec            hex filename

9735144 4970776 15474688        30180608        1cc8500 vmlinux.old
9735119 4970776 15474688        30180583        1cc84e7 vmlinux

Signed-off-by: Alexander Kuleshov <kuleshovm...@gmail.com>
---
 arch/x86/kernel/head64.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index f129a9a..4260ac4 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -40,13 +40,8 @@ pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE & 
~(_PAGE_GLOBAL | _PAGE_NX);
 /* Wipe all early page tables except for the kernel symbol map */
 static void __init reset_early_page_tables(void)
 {
-       unsigned long i;
-
-       for (i = 0; i < PTRS_PER_PGD-1; i++)
-               early_level4_pgt[i].pgd = 0;
-
+       memset(early_level4_pgt, 0, sizeof(pgd_t) * (PTRS_PER_PGD-1));
        next_early_pgt = 0;
-
        write_cr3(__pa_nodebug(early_level4_pgt));
 }
 
@@ -54,7 +49,6 @@ static void __init reset_early_page_tables(void)
 int __init early_make_pgtable(unsigned long address)
 {
        unsigned long physaddr = address - __PAGE_OFFSET;
-       unsigned long i;
        pgdval_t pgd, *pgd_p;
        pudval_t pud, *pud_p;
        pmdval_t pmd, *pmd_p;
@@ -81,8 +75,7 @@ again:
                }
 
                pud_p = (pudval_t *)early_dynamic_pgts[next_early_pgt++];
-               for (i = 0; i < PTRS_PER_PUD; i++)
-                       pud_p[i] = 0;
+               memset(pud_p, 0, sizeof(pud_p) * PTRS_PER_PUD);
                *pgd_p = (pgdval_t)pud_p - __START_KERNEL_map + phys_base + 
_KERNPG_TABLE;
        }
        pud_p += pud_index(address);
@@ -97,8 +90,7 @@ again:
                }
 
                pmd_p = (pmdval_t *)early_dynamic_pgts[next_early_pgt++];
-               for (i = 0; i < PTRS_PER_PMD; i++)
-                       pmd_p[i] = 0;
+               memset(pmd_p, 0, sizeof(pmd_p) * PTRS_PER_PMD);
                *pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + 
_KERNPG_TABLE;
        }
        pmd = (physaddr & PMD_MASK) + early_pmd_flags;
-- 
2.7.0.25.gfc10eb5