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Subject[PATCH] msync: check pte dirty earlier
From: Abhijit Karmarkar <abhijitk@veritas.com>

It's common practice to msync a large address range regularly, in which
often only a few ptes have actually been dirtied since the previous pass.

sync_pte_range then goes much faster if it tests whether pte is dirty
before locating and accessing each struct page cacheline; and it is hardly
slowed by ptep_clear_flush_dirty repeating that test in the opposite case,
when every pte actually is dirty.

But beware, s390's pte_dirty always says false, since its dirty bit is
kept in the storage key, located via the struct page address. So skip
this optimization in its case: use a pte_maybe_dirty macro which just
says true if page_test_and_clear_dirty is implemented.

Signed-off-by: Abhijit Karmarkar <abhijitk@veritas.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
---

include/asm-generic/pgtable.h | 3 +++
mm/msync.c | 2 ++
2 files changed, 5 insertions(+)

--- 2.6.12-rc6/include/asm-generic/pgtable.h 2005-05-25 18:09:09.000000000 +0100
+++ linux/include/asm-generic/pgtable.h 2005-06-04 20:41:55.000000000 +0100
@@ -125,6 +125,9 @@ static inline void ptep_set_wrprotect(st

#ifndef __HAVE_ARCH_PAGE_TEST_AND_CLEAR_DIRTY
#define page_test_and_clear_dirty(page) (0)
+#define pte_maybe_dirty(pte) pte_dirty(pte)
+#else
+#define pte_maybe_dirty(pte) (1)
#endif

#ifndef __HAVE_ARCH_PAGE_TEST_AND_CLEAR_YOUNG
--- 2.6.12-rc6/mm/msync.c 2005-05-25 18:09:21.000000000 +0100
+++ linux/mm/msync.c 2005-06-04 20:41:55.000000000 +0100
@@ -34,6 +34,8 @@ static void sync_pte_range(struct vm_are

if (!pte_present(*pte))
continue;
+ if (!pte_maybe_dirty(*pte))
+ continue;
pfn = pte_pfn(*pte);
if (!pfn_valid(pfn))
continue;
-
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