The patch titled
#ifdef very expensive debug check in page fault path
has been added to the -mm tree. Its filename is
ifdef-very-expensive-debug-check-in-page-fault-path.patch
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------------------------------------------------------
Subject: #ifdef very expensive debug check in page fault path
From: Carsten Otte <cotte@xxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 2 ++
1 file changed, 2 insertions(+)
diff -puN mm/memory.c~ifdef-very-expensive-debug-check-in-page-fault-path mm/memory.c
--- a/mm/memory.c~ifdef-very-expensive-debug-check-in-page-fault-path
+++ a/mm/memory.c
@@ -392,6 +392,7 @@ struct page *vm_normal_page(struct vm_ar
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_ar
print_bad_pte(vma, pte, addr);
return NULL;
}
+#endif
/*
* NOTE! We still have PageReserved() pages in the page
_
Patches currently in -mm which might be from cotte@xxxxxxxxxx are
origin.patch
ifdef-very-expensive-debug-check-in-page-fault-path.patch
git-kvm.patch
check-advice-of-fadvice64_64-even-if-get_xip_page-is-given.patch
ext2-xip-check-fix.patch
-
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