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_task_struct(p);
return;
}
if (__ratelimit(&oom_rs))
dump_header(p, gfp_mask, order, memcg, nodemask);
task_lock(p);
pr_err("%s: Kill process %d (%s) score %d or sacrifice child\n",
message, task_pid_nr(p), p->comm, points);
task_unlock(p);
/*
* If any of p's children has a different mm and is eligible for kill,
* the one with the highest oom_badness() score is sacrificed for its
* parent. This attempts to lose the minimal amount of work done while
* still freeing memory.
*/
read_lock(&tasklist_lock);
for_each_thread(p, t) {
list_for_each_entry(child, &t->children, sibling) {
unsigned int child_points;
if (child->mm == p->mm)
continue;
/*
* oom_badness() returns 0 if the thread is unkillable
*/
child_points = oom_badness(child, memcg, nodemask,
totalpages);
if (child_points > victim_points) {
put_task_struct(victim);
victim = child;
victim_points = child_points;
get_task_struct(victim);
}
}
}
read_unlock(&tasklist_lock);
p = find_lock_task_mm(victim);
if (!p) {
put_task_struct(victim);
return;
} else if (victim != p) {
get_task_struct(p);
put_task_struct(victim);
victim = p;
}
/* mm cannot safely be dereferenced after task_unlock(victim) */
mm = victim->mm;
pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
K(get_mm_counter(victim->mm, MM_ANONPAGES)),
K(get_mm_counter(victim->mm, MM_FILEPAGES)));
task_unlock(victim);
/*
* Kill all user processes sharing victim->mm in other thread groups, if
* any. They don't get access to memory reserves, though, to avoid
* depletion of all memory. This prevents mm->mmap_sem livelock when an
* oom killed thread cannot exit because it requires the semaphore and
* its contended by another thread trying to allocate memory itself.
* That thread will now get access to memory reserves since it has a
* pending fatal signal.
*/
rcu_read_lock();
for_each_process(p)
if (p->mm == mm && !same_thread_group(p, victim) &&
!(p->flags & PF_KTHREAD)) {
if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
continue;
task_lock(p); /* Protect ->comm from prctl() */
pr_err("Kill process %d (%s) sharing same memory\n",
task_pid_nr(p), p->comm);
task_unlock(p);
do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
}
rcu_read_unlock();
set_tsk_thread_flag(victim, TIF_MEMDIE);
do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
put_task_struct(victim);
}
该函数将会判断当前被kill的进程情况，如果该进程处于退出状态，则设置TIF_MEMDIE标志，不做kill操作；接着会通过list_for_each_entry()遍历该进程的子进程信息，如果某个子进程拥有不同的mm且合适被kill掉，将会优先考虑将该子进程替代父进程kill掉，这样可以避免kill掉父进程带来的接管子进程的工作开销；再往下通过find_lock_task_mm()找到持有mm锁的进程，如果进程处于退出状态，则return，否则继续处理，若此时的进程与传入的不是同一个时则更新victim；继而接着通过for_each_process()查找与当前被kill进程使用到了同样的共享内存的进程进行一起kill掉，kill之前将对应的进程添加标识TIF_MEMDIE，而kill的动作则是通过发送SICKILL信号给对应进程，由被kill进程从内核态返回用户态时进行处理。
至此，OOM kill处理分析完毕。
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