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| author | Carsten Otte <cotte@de.ibm.com> | 2008-01-17 15:21:17 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-01-17 15:38:59 -0800 |
| commit | 9723198c219f3546982cb469e5aed26e68399055 (patch) | |
| tree | b8e195cb1ca1bdf143e4e564fdb43f09aadfd6f3 /mm | |
| parent | 6b2d2cec1081a979e0efd6a1e9559e5a01a3c10e (diff) | |
| download | linux-9723198c219f3546982cb469e5aed26e68399055.tar.gz linux-9723198c219f3546982cb469e5aed26e68399055.tar.bz2 linux-9723198c219f3546982cb469e5aed26e68399055.zip | |
#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 <cotte@de.ibm.com>
Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/memory.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c index 4bf0b6d0eb2a..6dd1cd88bfb6 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; } +#ifdef CONFIG_DEBUG_VM /* * 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; } +#endif /* * NOTE! We still have PageReserved() pages in the page |