From: Nick Piggin <nickpiggin@yahoo.com.au>
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 <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
mm/mremap.c | 4 ++++
1 files changed, 4 insertions(+)
diff -puN mm/mremap.c~mm-remap-zero_page-mappings mm/mremap.c
--- 25/mm/mremap.c~mm-remap-zero_page-mappings Tue Jul 26 13:29:24 2005
+++ 25-akpm/mm/mremap.c Tue Jul 26 13:29:24 2005
@@ -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;
_