• Paul Jackson's avatar
    [PATCH] cpuset: rework cpuset_zone_allowed api · 02a0e53d
    Paul Jackson authored
    Elaborate the API for calling cpuset_zone_allowed(), so that users have to
    explicitly choose between the two variants:
    Until now, whether or not you got the hardwall flavor depended solely on
    whether or not you or'd in the __GFP_HARDWALL gfp flag to the gfp_mask
    If you didn't specify __GFP_HARDWALL, you implicitly got the softwall
    Unfortunately, this meant that users would end up with the softwall version
    without thinking about it.  Since only the softwall version might sleep,
    this led to bugs with possible sleeping in interrupt context on more than
    one occassion.
    The hardwall version requires that the current tasks mems_allowed allows
    the node of the specified zone (or that you're in interrupt or that
    __GFP_THISNODE is set or that you're on a one cpuset system.)
    The softwall version, depending on the gfp_mask, might allow a node if it
    was allowed in the nearest enclusing cpuset marked mem_exclusive (which
    requires taking the cpuset lock 'callback_mutex' to evaluate.)
    This patch removes the cpuset_zone_allowed() call, and forces the caller to
    explicitly choose between the hardwall and the softwall case.
    If the caller wants the gfp_mask to determine this choice, they should (1)
    be sure they can sleep or that __GFP_HARDWALL is set, and (2) invoke the
    cpuset_zone_allowed_softwall() routine.
    This adds another 100 or 200 bytes to the kernel text space, due to the few
    lines of nearly duplicate code at the top of both cpuset_zone_allowed_*
    routines.  It should save a few instructions executed for the calls that
    turned into calls of cpuset_zone_allowed_hardwall, thanks to not having to
    set (before the call) then check (within the call) the __GFP_HARDWALL flag.
    For the most critical call, from get_page_from_freelist(), the same
    instructions are executed as before -- the old cpuset_zone_allowed()
    routine it used to call is the same code as the
    cpuset_zone_allowed_softwall() routine that it calls now.
    Not a perfect win, but seems worth it, to reduce this chance of hitting a
    sleeping with irq off complaint again.
    Signed-off-by: default avatarPaul Jackson <pj@sgi.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>