• KAMEZAWA Hiroyuki's avatar
    memcg: fix direct softlimit reclaim to be called in limit path · ac34a1a3
    KAMEZAWA Hiroyuki authored
    Commit d149e3b2 ("memcg: add the soft_limit reclaim in global direct
    reclaim") adds a softlimit hook to shrink_zones().  By this, soft limit
    is called as
    
       try_to_free_pages()
           do_try_to_free_pages()
               shrink_zones()
                   mem_cgroup_soft_limit_reclaim()
    
    Then, direct reclaim is memcg softlimit hint aware, now.
    
    But, the memory cgroup's "limit" path can call softlimit shrinker.
    
       try_to_free_mem_cgroup_pages()
           do_try_to_free_pages()
               shrink_zones()
                   mem_cgroup_soft_limit_reclaim()
    
    This will cause a global reclaim when a memcg hits limit.
    
    This is bug. soft_limit_reclaim() should be called when
    scanning_global_lru(sc) == true.
    
    And the commit adds a variable "total_scanned" for counting softlimit
    scanned pages....it's not "total".  This patch removes the variable and
    update sc->nr_scanned instead of it.  This will affect shrink_slab()'s
    scan condition but, global LRU is scanned by softlimit and I think this
    change makes sense.
    
    TODO: avoid too much scanning of a zone when softlimit did enough work.
    Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    Cc: Ying Han <yinghan@google.com>
    Cc: Michal Hocko <mhocko@suse.cz>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    ac34a1a3
vmscan.c 95 KB