• Miao Xie's avatar
    cpuset,mm: update tasks' mems_allowed in time · 58568d2a
    Miao Xie authored
    Fix allocating page cache/slab object on the unallowed node when memory
    spread is set by updating tasks' mems_allowed after its cpuset's mems is
    changed.
    
    In order to update tasks' mems_allowed in time, we must modify the code of
    memory policy.  Because the memory policy is applied in the process's
    context originally.  After applying this patch, one task directly
    manipulates anothers mems_allowed, and we use alloc_lock in the
    task_struct to protect mems_allowed and memory policy of the task.
    
    But in the fast path, we didn't use lock to protect them, because adding a
    lock may lead to performance regression.  But if we don't add a lock,the
    task might see no nodes when changing cpuset's mems_allowed to some
    non-overlapping set.  In order to avoid it, we set all new allowed nodes,
    then clear newly disallowed ones.
    
    [lee.schermerhorn@hp.com:
      The rework of mpol_new() to extract the adjusting of the node mask to
      apply cpuset and mpol flags "context" breaks set_mempolicy() and mbind()
      with MPOL_PREFERRED and a NULL nodemask--i.e., explicit local
      allocation.  Fix this by adding the check for MPOL_PREFERRED and empty
      node mask to mpol_new_mpolicy().
    
      Remove the now unneeded 'nodes = NULL' from mpol_new().
    
      Note that mpol_new_mempolicy() is always called with a non-NULL
      'nodes' parameter now that it has been removed from mpol_new().
      Therefore, we don't need to test nodes for NULL before testing it for
      'empty'.  However, just to be extra paranoid, add a VM_BUG_ON() to
      verify this assumption.]
    [lee.schermerhorn@hp.com:
    
      I don't think the function name 'mpol_new_mempolicy' is descriptive
      enough to differentiate it from mpol_new().
    
      This function applies cpuset set context, usually constraining nodes
      to those allowed by the cpuset.  However, when the 'RELATIVE_NODES flag
      is set, it also translates the nodes.  So I settled on
      'mpol_set_nodemask()', because the comment block for mpol_new() mentions
      that we need to call this function to "set nodes".
    
      Some additional minor line length, whitespace and typo cleanup.]
    Signed-off-by: default avatarMiao Xie <miaox@cn.fujitsu.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Christoph Lameter <cl@linux-foundation.org>
    Cc: Paul Menage <menage@google.com>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
    Cc: Pekka Enberg <penberg@cs.helsinki.fi>
    Cc: David Rientjes <rientjes@google.com>
    Signed-off-by: default avatarLee Schermerhorn <lee.schermerhorn@hp.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    58568d2a
kthread.c 7.27 KB