Dave McCracken wrote on Tuesday, August 30, 2005 3:13 PM

This patch implements page table sharing for all shared memory regions that
span an entire page table page.  It supports sharing at multiple page
levels, depending on the architecture.


This version of the patch supports i386 and x86_64.  I have additional
patches to support ppc64, but they are not quite ready for public
consumption.

 ....
+		prio_tree_iter_init(&iter, &mapping->i_mmap,
+				    vma->vm_start, vma->vm_end);

I think this is a bug.  The radix priority tree for address_space->
i_mmap is keyed on vma->vm_pgoff.  Your patch uses the vma virtual
address to find a shareable range, Which will always fail a match
even though there is one.  The following is a quick hack I did to
make it work.

- Ken

--- linux-2.6.13/mm/ptshare.c.orig	2005-09-01 18:58:12.299321918 -0700
+++ linux-2.6.13/mm/ptshare.c	2005-09-01 18:58:39.846196580 -0700

@@ -26,6 +26,11 @@
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
 
+#define RADIX_INDEX(vma)  ((vma)->vm_pgoff)
+#define VMA_SIZE(vma)	  (((vma)->vm_end - (vma)->vm_start) >> PAGE_SHIFT)
+/* avoid overflow */
+#define HEAP_INDEX(vma)	  ((vma)->vm_pgoff + (VMA_SIZE(vma) - 1))
+
 #undef	PT_DEBUG
 
 #ifndef __PAGETABLE_PMD_FOLDED

@@ -173,7 +178,7 @@ pt_share_pte(struct vm_area_struct *vma,
 		       address);
 #endif
 		prio_tree_iter_init(&iter, &mapping->i_mmap,
-				    vma->vm_start, vma->vm_end);
+				    RADIX_INDEX(vma), HEAP_INDEX(vma));
 
 		while ((svma = next_shareable_vma(vma, svma, &iter))) {
 			spgd = pgd_offset(svma->vm_mm, address);


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