• Tetsuo Handa's avatar
    mm,oom: speed up select_bad_process() loop · f44666b0
    Tetsuo Handa authored
    Since commit 3a5dda7a ("oom: prevent unnecessary oom kills or kernel
    panics"), select_bad_process() is using for_each_process_thread().
    
    Since oom_unkillable_task() scans all threads in the caller's thread
    group and oom_task_origin() scans signal_struct of the caller's thread
    group, we don't need to call oom_unkillable_task() and oom_task_origin()
    on each thread.  Also, since !mm test will be done later at
    oom_badness(), we don't need to do !mm test on each thread.  Therefore,
    we only need to do TIF_MEMDIE test on each thread.
    
    Although the original code was correct it was quite inefficient because
    each thread group was scanned num_threads times which can be a lot
    especially with processes with many threads.  Even though the OOM is
    extremely cold path it is always good to be as effective as possible
    when we are inside rcu_read_lock() - aka unpreemptible context.
    
    If we track number of TIF_MEMDIE threads inside signal_struct, we don't
    need to do TIF_MEMDIE test on each thread.  This will allow
    select_bad_process() to use for_each_process().
    
    This patch adds a counter to signal_struct for tracking how many
    TIF_MEMDIE threads are in a given thread group, and check it at
    oom_scan_process_thread() so that select_bad_process() can use
    for_each_process() rather than for_each_process_thread().
    
    [mhocko@suse.com: do not blow the signal_struct size]
      Link: http://lkml.kernel.org/r/20160520075035.GF19172@dhcp22.suse.cz
    Link: http://lkml.kernel.org/r/201605182230.IDC73435.MVSOHLFOQFOJtF@I-love.SAKURA.ne.jpSigned-off-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Acked-by: default avatarMichal Hocko <mhocko@suse.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f44666b0
oom_kill.c 26.8 KB