Hugh Dickins wrote:
On Sun, 25 Mar 2007, David Rientjes wrote:
Add ptep_test_and_clear_{dirty,young} to i386. They advertise that they
have it and there is at least one place where it needs to be called
without the page table lock: to clear the accessed bit on write to
Without the page table lock??
/proc/pid/clear_refs.
ptep_clear_flush_{dirty,young} are updated to use the new functions. The
overall net effect to current users of ptep_clear_flush_{dirty,young} is
that we introduce an additional branch.
We need to Cc Zach on this: git blame indicates it was he who replaced
i386's ptep_test_and_clear_{dirty,young} by that "We don't actually
have these" comment - it looks a bit as if what you want to do might
violate the assumptions he wants to make, but I don't grasp it.
Hugh
Cc: Hugh Dickins <[EMAIL PROTECTED]>
Cc: Ingo Molnar <[EMAIL PROTECTED]>
Signed-off-by: David Rientjes <[EMAIL PROTECTED]>
---
include/asm-i386/pgtable.h | 25 +++++++++++++++++--------
1 files changed, 17 insertions(+), 8 deletions(-)
diff --git a/include/asm-i386/pgtable.h b/include/asm-i386/pgtable.h
--- a/include/asm-i386/pgtable.h
+++ b/include/asm-i386/pgtable.h
@@ -283,12 +283,23 @@ do {
\
} \
} while (0)
-/*
- * We don't actually have these, but we want to advertise them so that
- * we can encompass the flush here.
- */
#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_DIRTY
+static inline int ptep_test_and_clear_dirty(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *ptep)
+{
+ if (!pte_dirty(*ptep))
+ return 0;
+ return test_and_clear_bit(_PAGE_BIT_DIRTY, &ptep->pte_low);
+}
+
If you actually clear the bit, you need to:
+ pte_update_defer(vma->vm_mm, addr, ptep);
The reason is, when updating PTEs, the hypervisor must be notified.
Using atomic operations to do this is fine for all hypervisors I am
aware of. However, for hypervisors which shadow page tables, if these
PTE modifications are not trapped, you need a post-modification call to
fulfill the update of the shadow page table.
#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
+static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *ptep)
+{
+ if (!pte_young(*ptep))
+ return 0;
+ return test_and_clear_bit(_PAGE_BIT_ACCESSED, &ptep->pte_low);
+}
Same here.
Hugh, thanks for the cc.
Zach
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