• Michal Hocko's avatar
    mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj · 44a70ade
    Michal Hocko authored
    oom_score_adj is shared for the thread groups (via struct signal) but this
    is not sufficient to cover processes sharing mm (CLONE_VM without
    CLONE_SIGHAND) and so we can easily end up in a situation when some
    processes update their oom_score_adj and confuse the oom killer.  In the
    worst case some of those processes might hide from the oom killer
    altogether via OOM_SCORE_ADJ_MIN while others are eligible.  OOM killer
    would then pick up those eligible but won't be allowed to kill others
    sharing the same mm so the mm wouldn't release the mm and so the memory.
    
    It would be ideal to have the oom_score_adj per mm_struct because that is
    the natural entity OOM killer considers.  But this will not work because
    some programs are doing
    
    	vfork()
    	set_oom_adj()
    	exec()
    
    We can achieve the same though.  oom_score_adj write handler can set the
    oom_score_adj for all processes sharing the same mm if the task is not in
    the middle of vfork.  As a result all the processes will share the same
    oom_score_adj.  The current implementation is rather pessimistic and
    checks all the existing processes by default if there is more than 1
    holder of the mm but we do not have any reliable way to check for external
    users yet.
    
    Link: http://lkml.kernel.org/r/1466426628-15074-5-git-send-email-mhocko@kernel.orgSigned-off-by: default avatarMichal Hocko <mhocko@suse.com>
    Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
    Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    44a70ade
oom_kill.c 27.2 KB