• David Rientjes's avatar
    mempolicy: support optional mode flags · 028fec41
    David Rientjes authored
    With the evolution of mempolicies, it is necessary to support mempolicy mode
    flags that specify how the policy shall behave in certain circumstances.  The
    most immediate need for mode flag support is to suppress remapping the
    nodemask of a policy at the time of rebind.
    
    Both the mempolicy mode and flags are passed by the user in the 'int policy'
    formal of either the set_mempolicy() or mbind() syscall.  A new constant,
    MPOL_MODE_FLAGS, represents the union of legal optional flags that may be
    passed as part of this int.  Mempolicies that include illegal flags as part of
    their policy are rejected as invalid.
    
    An additional member to struct mempolicy is added to support the mode flags:
    
    	struct mempolicy {
    		...
    		unsigned short policy;
    		unsigned short flags;
    	}
    
    The splitting of the 'int' actual passed by the user is done in
    sys_set_mempolicy() and sys_mbind() for their respective syscalls.  This is
    done by intersecting the actual with MPOL_MODE_FLAGS, rejecting the syscall of
    there are additional flags, and storing it in the new 'flags' member of struct
    mempolicy.  The intersection of the actual with ~MPOL_MODE_FLAGS is stored in
    the 'policy' member of the struct and all current users of pol->policy remain
    unchanged.
    
    The union of the policy mode and optional mode flags is passed back to the
    user in get_mempolicy().
    
    This combination of mode and flags within the same actual does not break
    userspace code that relies on get_mempolicy(&policy, ...) and either
    
    	switch (policy) {
    	case MPOL_BIND:
    		...
    	case MPOL_INTERLEAVE:
    		...
    	};
    
    statements or
    
    	if (policy == MPOL_INTERLEAVE) {
    		...
    	}
    
    statements.  Such applications would need to use optional mode flags when
    calling set_mempolicy() or mbind() for these previously implemented statements
    to stop working.  If an application does start using optional mode flags, it
    will need to mask the optional flags off the policy in switch and conditional
    statements that only test mode.
    
    An additional member is also added to struct shmem_sb_info to store the
    optional mode flags.
    
    [hugh@veritas.com: shmem mpol: fix build warning]
    Cc: Paul Jackson <pj@sgi.com>
    Cc: Christoph Lameter <clameter@sgi.com>
    Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
    Cc: Andi Kleen <ak@suse.de>
    Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
    Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    028fec41
mempolicy.c 51.4 KB