[patch 2/14] mm:

Nick Piggin
2005-11-06T08:18:32Z

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2/14

--
SUSE Labs, Novell Inc.

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Prefetch ptes a line ahead. Worth 25% on ia64 when doing big forks.

Index: linux-2.6/include/asm-generic/pgtable.h
===================================================================
--- linux-2.6.orig/include/asm-generic/pgtable.h
+++ linux-2.6/include/asm-generic/pgtable.h
@@ -196,6 +196,33 @@ static inline void ptep_set_wrprotect(st
})
#endif

+#ifndef __HAVE_ARCH_PTE_PREFETCH
+#define PTES_PER_LINE (L1_CACHE_BYTES / sizeof(pte_t))
+#define PTE_LINE_MASK (~(PTES_PER_LINE - 1))
+#define ADDR_PER_LINE (PTES_PER_LINE << PAGE_SHIFT)
+#define ADDR_LINE_MASK (~(ADDR_PER_LINE - 1))
+
+#define pte_prefetch(pte, addr, end) \
+({ \
+ unsigned long __nextline = ((addr) + ADDR_PER_LINE) & ADDR_LINE_MASK; \
+ if (__nextline < (end)) \
+ prefetch(pte + PTES_PER_LINE); \
+})
+
+#define pte_prefetch_start(pte, addr, end) \
+({ \
+ prefetch(pte); \
+ pte_prefetch(pte, addr, end); \
+})
+
+#define pte_prefetch_next(pte, addr, end) \
+({ \
+ unsigned long __addr = (addr); \
+ if (!(__addr & ~ADDR_LINE_MASK)) /* We hit a new cacheline */ \
+ pte_prefetch(pte, __addr, end); \
+})
+#endif
+
#ifndef __ASSEMBLY__
/*
* When walking page tables, we usually want to skip any p?d_none entries;
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c
+++ linux-2.6/mm/memory.c
@@ -437,6 +437,8 @@ again:
if (!dst_pte)
return -ENOMEM;
src_pte = pte_offset_map_nested(src_pmd, addr);
+ pte_prefetch_start(src_pte, addr, end);
+
src_ptl = pte_lockptr(src_mm, src_pmd);
spin_lock(src_ptl);

@@ -458,7 +460,8 @@ again:
}
copy_one_pte(dst_mm, src_mm, dst_pte, src_pte, vma, addr, rss);
progress += 8;
- } while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);
+ } while (dst_pte++, src_pte++, addr += PAGE_SIZE,
+ pte_prefetch_next(src_pte, addr, end), addr != end);

spin_unlock(src_ptl);
pte_unmap_nested(src_pte - 1);
@@ -561,6 +564,7 @@ static unsigned long zap_pte_range(struc
int anon_rss = 0;

pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ pte_prefetch_start(pte, addr, end);
do {
pte_t ptent = *pte;
if (pte_none(ptent)) {
@@ -629,7 +633,8 @@ static unsigned long zap_pte_range(struc
if (!pte_file(ptent))
free_swap_and_cache(pte_to_swp_entry(ptent));
pte_clear_full(mm, addr, pte, tlb->fullmm);
- } while (pte++, addr += PAGE_SIZE, (addr != end && *zap_work > 0));
+ } while (pte++, addr += PAGE_SIZE, pte_prefetch_next(pte, addr, end),
+ (addr != end && *zap_work > 0));

add_mm_rss(mm, file_rss, anon_rss);
pte_unmap_unlock(pte - 1, ptl);