[patch 5/6] mm: remap ZERO_PAGE mappings
5/6
Remap ZERO_PAGE ptes when remapping memory. This is currently just an
optimisation for MIPS, which is the only architecture with multiple
zero pages - it now retains the mapping it needs for good cache performance,
and as well do_wp_page is now able to always correctly detect and
optimise zero page COW faults.
This change is required in order to be able to detect whether a pte
points to a ZERO_PAGE using only its (pte, vaddr) pair.
Signed-off-by: Nick Piggin <[EMAIL PROTECTED]>
Index: linux-2.6/mm/mremap.c
===
--- linux-2.6.orig/mm/mremap.c
+++ linux-2.6/mm/mremap.c
@@ -141,6 +141,10 @@ move_one_page(struct vm_area_struct *vma
if (dst) {
pte_t pte;
pte = ptep_clear_flush(vma, old_addr, src);
+ /* ZERO_PAGE can be dependant on virtual addr */
+ if (pfn_valid(pte_pfn(pte)) &&
+ pte_page(pte) == ZERO_PAGE(old_addr))
+ pte =
pte_wrprotect(mk_pte(ZERO_PAGE(new_addr), new_vma->vm_page_prot));
set_pte_at(mm, new_addr, dst, pte);
} else
error = -ENOMEM;
[patch 5/6] mm: remap ZERO_PAGE mappings
5/6
Remap ZERO_PAGE ptes when remapping memory. This is currently just an
optimisation for MIPS, which is the only architecture with multiple
zero pages - it now retains the mapping it needs for good cache performance,
and as well do_wp_page is now able to always correctly detect and
optimise zero page COW faults.
This change is required in order to be able to detect whether a pte
points to a ZERO_PAGE using only its (pte, vaddr) pair.
Signed-off-by: Nick Piggin [EMAIL PROTECTED]
Index: linux-2.6/mm/mremap.c
===
--- linux-2.6.orig/mm/mremap.c
+++ linux-2.6/mm/mremap.c
@@ -141,6 +141,10 @@ move_one_page(struct vm_area_struct *vma
if (dst) {
pte_t pte;
pte = ptep_clear_flush(vma, old_addr, src);
+ /* ZERO_PAGE can be dependant on virtual addr */
+ if (pfn_valid(pte_pfn(pte))
+ pte_page(pte) == ZERO_PAGE(old_addr))
+ pte =
pte_wrprotect(mk_pte(ZERO_PAGE(new_addr), new_vma-vm_page_prot));
set_pte_at(mm, new_addr, dst, pte);
} else
error = -ENOMEM;
