cvs commit: src/sys/vm vm_object.c

[Alan Cox]

alc         2005-02-23 16:45:13 UTC

  FreeBSD src repository

  Modified files:        (Branch: RELENG_5)
    sys/vm               vm_object.c 
  Log:
  MFC revisions 1.333 and 1.334
   Eliminate unnecessary calls to vm_page_busy().
  
  MFC revision 1.340
   Move the acquisition and release of the page queues lock outside of a loop
   in vm_object_split() to avoid repeated acquisition and release.
  
  MFC revision 1.343
   Consider three objects, O, BO, and BBO, where BO is O's backing object
   and BBO is BO's backing object.  Now, suppose that O and BO are being
   collapsed.  Furthermore, suppose that BO has been marked dead
   (OBJ_DEAD) by vm_object_backing_scan() and that either
   vm_object_backing_scan() has been forced to sleep due to encountering
   a busy page or vm_object_collapse() has been forced to sleep due to
   memory allocation in the swap pager.  If vm_object_deallocate() is
   then called on BBO and BO is BBO's only shadow object,
   vm_object_deallocate() will collapse BO and BBO.  In doing so, it adds
   a necessary temporary reference to BO.  If this collapse also sleeps
   and the prior collapse resumes first, the temporary reference will
   cause vm_object_collapse to panic with the message "backing_object %p
   was somehow re-referenced during collapse!"
  
   Resolve this race by changing vm_object_deallocate() such that it
   doesn't collapse BO and BBO if BO is marked dead.  Once O and BO are
   collapsed, vm_object_collapse() will attempt to collapse O and BBO.
   So, vm_object_deallocate() on BBO need do nothing.
  
  MFC revision 1.345
   Update the text of an assertion to reflect changes made in revision 1.148.
  
   Eliminate an unnecessary, temporary increment of the backing object's
   reference count in vm_object_qcollapse().
  
  Revision   Changes    Path
  1.331.2.3  +12 -12    src/sys/vm/vm_object.c