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authorCarsten Otte <cotte@de.ibm.com>2008-01-17 15:21:17 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-01-17 15:38:59 -0800
commit9723198c219f3546982cb469e5aed26e68399055 (patch)
treeb8e195cb1ca1bdf143e4e564fdb43f09aadfd6f3 /mm
parentalpha: fix conversion from denormal float to double (diff)
downloadlinux-dev-9723198c219f3546982cb469e5aed26e68399055.tar.xz
linux-dev-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.c2
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