K 10
svn:author
V 6
dillon
K 8
svn:date
V 27
1999-01-22T05:49:39.000000Z
K 7
svn:log
V 965
    Backport from -4.x.  We are supposed to wait while the page is busy before
    messing with it, but the VM code was special-casing a m->busy page that
    was still valid ( i.e. usually a pageout ) and allowing it through.  The
    problem is that whatever m->busy'd the page is probably still depending on
    it not being messed with.  Specifically, I am thinking of the
    vm_pager_get_pages() code where the OBJT_VNODE pager converts PG_BUSY
    to m->busy for the read operation.    While this code may not be
    specifically broken for the case, it does initially set PG_BUSY and assume
    that it has the entire page to itself... but OBJT_VNODE converts it to
    m->busy.  It is just too dangerous to allow the special case optimization
    through.

    Removing the special optimization should have no discernable effect since
    pageout operates mark resident pmap pte's READ-ONLY rather then unmapping
    them, and so no fault normally occurs.

END