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SubjectRe: [PATCH] mm, oom_adj: avoid meaningless loop to find processes sharing mm
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On 2018/10/08 10:19, Yong-Taek Lee wrote:
> @@ -1056,6 +1056,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> struct mm_struct *mm = NULL;
> struct task_struct *task;
> int err = 0;
> + int mm_users = 0;
>
> task = get_proc_task(file_inode(file));
> if (!task)
> @@ -1092,7 +1093,8 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> struct task_struct *p = find_lock_task_mm(task);
>
> if (p) {
> - if (atomic_read(&p->mm->mm_users) > 1) {
> + mm_users = atomic_read(&p->mm->mm_users);
> + if ((mm_users > 1) && (mm_users != get_nr_threads(p))) {

How can this work (even before this patch)? When clone(CLONE_VM without CLONE_THREAD/CLONE_SIGHAND)
is requested, copy_process() calls copy_signal() in order to copy sig->oom_score_adj and
sig->oom_score_adj_min before calling copy_mm() in order to increment mm->mm_users, doesn't it?
Then, we will get two different "struct signal_struct" with different oom_score_adj/oom_score_adj_min
but one "struct mm_struct" shared by two thread groups.

> mm = p->mm;
> atomic_inc(&mm->mm_count);
> }

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