cvs commit: src/sys/vm vm_fault.c vm_map.c

[Alan Cox]

alc         2007-05-22 04:46:00 UTC

  FreeBSD src repository

  Modified files:
    sys/vm               vm_fault.c vm_map.c 
  Log:
  Eliminate the reactivation of cached pages in vm_fault_prefault() and
  vm_map_pmap_enter() unless the caller is madvise(MADV_WILLNEED).  With
  the exception of calls to vm_map_pmap_enter() from
  madvise(MADV_WILLNEED), vm_fault_prefault() and vm_map_pmap_enter()
  are both used to create speculative mappings.  Thus, always
  reactivating cached pages is a mistake.  In principle, cached pages
  should only be reactivated by an actual access.  Otherwise, the
  following misbehavior can occur.  On a hard fault for a text page the
  clustering algorithm fetches not only the required page but also
  several of the adjacent pages.  Now, suppose that one or more of the
  adjacent pages are never accessed.  Ultimately, these unused pages
  become cached pages through the efforts of the page daemon.  However,
  the next activation of the executable reactivates and maps these
  unused pages.  Consequently, they are never replaced.  In effect, they
  become pinned in memory.
  
  Revision  Changes    Path
  1.228     +3 -3      src/sys/vm/vm_fault.c
  1.384     +13 -5     src/sys/vm/vm_map.c