• Michal Hocko's avatar
    vmscan: memcg: always use swappiness of the reclaimed memcg · 688eb988
    Michal Hocko authored
    Memory reclaim always uses swappiness of the reclaim target memcg
    (origin of the memory pressure) or vm_swappiness for global memory
    reclaim.  This behavior was consistent (except for difference between
    global and hard limit reclaim) because swappiness was enforced to be
    consistent within each memcg hierarchy.
    
    After "mm: memcontrol: remove hierarchy restrictions for swappiness and
    oom_control" each memcg can have its own swappiness independent of
    hierarchical parents, though, so the consistency guarantee is gone.
    This can lead to an unexpected behavior.  Say that a group is explicitly
    configured to not swapout by memory.swappiness=0 but its memory gets
    swapped out anyway when the memory pressure comes from its parent with a
    It is also unexpected that the knob is meaningless without setting the
    hard limit which would trigger the reclaim and enforce the swappiness.
    There are setups where the hard limit is configured higher in the
    hierarchy by an administrator and children groups are under control of
    somebody else who is interested in the swapout behavior but not
    necessarily about the memory limit.
    
    From a semantic point of view swappiness is an attribute defining anon
    vs.
     file proportional scanning of LRU which is memcg specific (unlike
    charges which are propagated up the hierarchy) so it should be applied
    to the particular memcg's LRU regardless where the memory pressure comes
    from.
    
    This patch removes vmscan_swappiness() and stores the swappiness into
    the scan_control structure.  mem_cgroup_swappiness is then used to
    provide the correct value before shrink_lruvec is called.  The global
    vm_swappiness is used for the root memcg.
    
    [hughd@google.com: oopses immediately when booted with cgroup_disable=memory]
    Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
    Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Cc: Tejun Heo <tj@kernel.org>
    Signed-off-by: default avatarHugh Dickins <hughd@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    688eb988
memory.txt 36.1 KB