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    mempolicy: use struct mempolicy pointer in shmem_sb_info · 71fe804b
    Lee Schermerhorn 提交于
    This patch replaces the mempolicy mode, mode_flags, and nodemask in the
    shmem_sb_info struct with a struct mempolicy pointer, initialized to NULL.
    This removes dependency on the details of mempolicy from shmem.c and hugetlbfs
    inode.c and simplifies the interfaces.
    
    mpol_parse_str() in mempolicy.c is changed to return, via a pointer to a
    pointer arg, a struct mempolicy pointer on success.  For MPOL_DEFAULT, the
    returned pointer is NULL.  Further, mpol_parse_str() now takes a 'no_context'
    argument that causes the input nodemask to be stored in the w.user_nodemask of
    the created mempolicy for use when the mempolicy is installed in a tmpfs inode
    shared policy tree.  At that time, any cpuset contextualization is applied to
    the original input nodemask.  This preserves the previous behavior where the
    input nodemask was stored in the superblock.  We can think of the returned
    mempolicy as "context free".
    
    Because mpol_parse_str() is now calling mpol_new(), we can remove from
    mpol_to_str() the semantic checks that mpol_new() already performs.
    
    Add 'no_context' parameter to mpol_to_str() to specify that it should format
    the nodemask in w.user_nodemask for 'bind' and 'interleave' policies.
    
    Change mpol_shared_policy_init() to take a pointer to a "context free" struct
    mempolicy and to create a new, "contextualized" mempolicy using the mode,
    mode_flags and user_nodemask from the input mempolicy.
    
      Note: we know that the mempolicy passed to mpol_to_str() or
      mpol_shared_policy_init() from a tmpfs superblock is "context free".  This
      is currently the only instance thereof.  However, if we found more uses for
      this concept, and introduced any ambiguity as to whether a mempolicy was
      context free or not, we could add another internal mode flag to identify
      context free mempolicies.  Then, we could remove the 'no_context' argument
      from mpol_to_str().
    
    Added shmem_get_sbmpol() to return a reference counted superblock mempolicy,
    if one exists, to pass to mpol_shared_policy_init().  We must add the
    reference under the sb stat_lock to prevent races with replacement of the mpol
    by remount.  This reference is removed in mpol_shared_policy_init().
    
    [akpm@linux-foundation.org: build fix]
    [akpm@linux-foundation.org: another build fix]
    [akpm@linux-foundation.org: yet another build fix]
    Signed-off-by: NLee Schermerhorn <lee.schermerhorn@hp.com>
    Cc: Christoph Lameter <clameter@sgi.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Andi Kleen <ak@suse.de>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    71fe804b
inode.c 23.1 KB