• Mel Gorman's avatar
    mm: disable zone_reclaim_mode by default · 4f9b16a6
    Mel Gorman authored
    When it was introduced, zone_reclaim_mode made sense as NUMA distances
    punished and workloads were generally partitioned to fit into a NUMA
    node.  NUMA machines are now common but few of the workloads are
    NUMA-aware and it's routine to see major performance degradation due to
    zone_reclaim_mode being enabled but relatively few can identify the
    problem.
    
    Those that require zone_reclaim_mode are likely to be able to detect
    when it needs to be enabled and tune appropriately so lets have a
    sensible default for the bulk of users.
    
    This patch (of 2):
    
    zone_reclaim_mode causes processes to prefer reclaiming memory from
    local node instead of spilling over to other nodes.  This made sense
    initially when NUMA machines were almost exclusively HPC and the
    workload was partitioned into nodes.  The NUMA penalties were
    sufficiently high to justify reclaiming the memory.  On current machines
    and workloads it is often the case that zone_reclaim_mode destroys
    performance but not all users know how to detect this.  Favour the
    common case and disable it by default.  Users that are sophisticated
    enough to know they need zone_reclaim_mode will detect it.
    Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
    Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Reviewed-by: default avatarZhang Yanfei <zhangyanfei@cn.fujitsu.com>
    Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
    Reviewed-by: default avatarChristoph Lameter <cl@linux.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    4f9b16a6
vm.txt 28.9 KB