[PATCH] consolidate the VMA splitting code

Patch from Christoph Hellwig.  250 lines of code go away.

The three syscalls madvice/mlock/mprotect all change attributes of
memory regions.  These attributes are stored in vm_area_structs (VMAs).

The current code for those syscalls does this by having four
subroutines each, for changing a whole VMA, one for just setting new
flags if a full VMA is affected, one that creates a new VMA in the
right part of the old one and sets the flags there, one for the left
part, and one that splits of both the left and the right part and sets
the new flags in the middle.

This patch makes those routines create new VMAs on the left and on te
right hand first and then always setting the flags in the old VMA.
Together with using a library function (split_vma) to to the split this
simplies the code and makes it more readable.  As a side affect it
fixes some VM accounting bugs observed by Hugh Dickins.

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e33d3f2bd080..3b7f9ba55dc0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -504,6 +504,8 @@ extern int expand_stack(struct vm_area_struct * vma, unsigned long address);
 extern struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr);
 extern struct vm_area_struct * find_vma_prev(struct mm_struct * mm, unsigned long addr,
 					     struct vm_area_struct **pprev);
+extern int split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
+		     unsigned long addr, int new_below);
 
 /* Look up the first VMA which intersects the interval start_addr..end_addr-1,
    NULL if none.  Assume start_addr < end_addr. */