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Feng Tang
7858d7bca7
MPOL_LOCAL policy has been setup as a real policy, but it is still handled like a faked POL_PREFERRED policy with one internal MPOL_F_LOCAL flag bit set, and there are many places having to judge the real 'prefer' or the 'local' policy, which are quite confusing. In current code, there are 4 cases that MPOL_LOCAL are used: 1. user specifies 'local' policy 2. user specifies 'prefer' policy, but with empty nodemask 3. system 'default' policy is used 4. 'prefer' policy + valid 'preferred' node with MPOL_F_STATIC_NODES flag set, and when it is 'rebind' to a nodemask which doesn't contains the 'preferred' node, it will perform as 'local' policy So make 'local' a real policy instead of a fake 'prefer' one, and kill MPOL_F_LOCAL bit, which can greatly reduce the confusion for code reading. For case 4, the logic of mpol_rebind_preferred() is confusing, as Michal Hocko pointed out: : I do believe that rebinding preferred policy is just bogus and it should : be dropped altogether on the ground that a preference is a mere hint from : userspace where to start the allocation. Unless I am missing something : cpusets will be always authoritative for the final placement. The : preferred node just acts as a starting point and it should be really : preserved when cpusets changes. Otherwise we have a very subtle behavior : corner cases. So dump all the tricky transformation between 'prefer' and 'local', and just record the new nodemask of rebinding. [[email protected]: fix a problem in mpol_set_nodemask(), per Michal Hocko] Link: https://lkml.kernel.org/r/[email protected] [[email protected]: refine code and comments of mpol_set_nodemask(), per Michal] Link: https://lkml.kernel.org/r/[email protected] Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Feng Tang <[email protected]> Suggested-by: Michal Hocko <[email protected]> Acked-by: Michal Hocko <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Andrea Arcangeli <[email protected]> Cc: Ben Widawsky <[email protected]> Cc: Dan Williams <[email protected]> Cc: Dave Hansen <[email protected]> Cc: David Rientjes <[email protected]> Cc: Huang Ying <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Mike Kravetz <[email protected]> Cc: Randy Dunlap <[email protected]> Cc: Vlastimil Babka <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>