Prevent the leakage of wired pages in the following circumstances:

First, a file is mmap(2)ed and then mlock(2)ed.  Later, it is truncated.
Under "normal" circumstances, i.e., when the file is not mlock(2)ed, the
pages beyond the EOF are unmapped and freed.  However, when the file is
mlock(2)ed, the pages beyond the EOF are unmapped but not freed because
they have a non-zero wire count.  This can be a mistake.  Specifically,
it is a mistake if the sole reason why the pages are wired is because of
wired, managed mappings.  Previously, unmapping the pages destroys these
wired, managed mappings, but does not reduce the pages' wire count.
Consequently, when the file is unmapped, the pages are not unwired
because the wired mapping has been destroyed.  Moreover, when the vm
object is finally destroyed, the pages are leaked because they are still
wired.  The fix is to reduce the pages' wired count by the number of
wired, managed mappings destroyed.  To do this, I introduce a new pmap
function pmap_page_wired_mappings() that returns the number of managed
mappings to the given physical page that are wired, and I use this
function in vm_object_page_remove().

Reviewed by: tegge
MFC after: 6 weeks

1 files changed, 1 insertions, 0 deletions

diff --git a/sys/vm/pmap.h b/sys/vm/pmap.h
index 3d9045f..61c5fa6 100644
--- a/sys/vm/pmap.h
+++ b/sys/vm/pmap.h
@@ -114,6 +114,7 @@ void		 pmap_object_init_pt(pmap_t pmap, vm_offset_t addr,
 		    vm_object_t object, vm_pindex_t pindex, vm_size_t size);
 boolean_t	 pmap_page_exists_quick(pmap_t pmap, vm_page_t m);
 void		 pmap_page_init(vm_page_t m);
+int		 pmap_page_wired_mappings(vm_page_t m);
 int		 pmap_pinit(pmap_t);
 void		 pmap_pinit0(pmap_t);
 void		 pmap_protect(pmap_t, vm_offset_t, vm_offset_t, vm_prot_t);