Commit:     9723198c219f3546982cb469e5aed26e68399055
Parent:     6b2d2cec1081a979e0efd6a1e9559e5a01a3c10e
Author:     Carsten Otte <[EMAIL PROTECTED]>
AuthorDate: Thu Jan 17 15:21:17 2008 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Thu Jan 17 15:38:59 2008 -0800

    #ifdef very expensive debug check in page fault path
    This patch puts #ifdef CONFIG_DEBUG_VM around a check in vm_normal_page
    that verifies that a pfn is valid.  This patch increases performance of the
    page fault microbenchmark in lmbench by 13% and overall dbench performance
    by 7% on s390x.  pfn_valid() is an expensive operation on s390 that needs a
    high double digit amount of CPU cycles.  Nick Piggin suggested that
    pfn_valid() involves an array lookup on systems with sparsemem, and
    therefore is an expensive operation there too.
    The check looks like a clear debug thing to me, it should never trigger on
    regular kernels.  And if a pte is created for an invalid pfn, we'll find
    out once the memory gets accessed later on anyway.  Please consider
    inclusion of this patch into mm.
    Signed-off-by: Carsten Otte <[EMAIL PROTECTED]>
    Acked-by: Nick Piggin <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
 mm/memory.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 4bf0b6d..6dd1cd8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -392,6 +392,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, 
unsigned long addr, pte_
                        return NULL;
         * Add some anal sanity checks for now. Eventually,
         * we should just do "return pfn_to_page(pfn)", but
@@ -402,6 +403,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, 
unsigned long addr, pte_
                print_bad_pte(vma, pte, addr);
                return NULL;
         * NOTE! We still have PageReserved() pages in the page 
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