[PATCH] KVM: no need to test bit before setting dirty bit these days

[Takuya Yoshikawa]

As Avi pointed out, testing bit part in mark_page_dirty() was important
in the days of shadow paging, but currently EPT and NPT has already become
common and the chance of faulting a page more that once per iteration is
small. So let's remove the test bit to avoid extra access.

Signed-off-by: Takuya Yoshikawa yoshikawa.tak...@oss.ntt.co.jp
---
 virt/kvm/kvm_main.c |4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6dc9404..9ab1a77 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1192,9 +1192,7 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
if (memslot  memslot-dirty_bitmap) {
unsigned long rel_gfn = gfn - memslot-base_gfn;
 
-   /* avoid RMW */
-   if (!generic_test_le_bit(rel_gfn, memslot-dirty_bitmap))
-   generic___set_le_bit(rel_gfn, memslot-dirty_bitmap);
+   generic___set_le_bit(rel_gfn, memslot-dirty_bitmap);
}
 }
 
-- 
1.6.3.3

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Re: [PATCH] KVM: no need to test bit before setting dirty bit these days

[Avi Kivity]

On 04/23/2010 11:48 AM, Takuya Yoshikawa wrote:

As Avi pointed out, testing bit part in mark_page_dirty() was important
in the days of shadow paging, but currently EPT and NPT has already become
common and the chance of faulting a page more that once per iteration is
small. So let's remove the test bit to avoid extra access.
   


Applied, thanks.

--
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.

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