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    SubjectRe: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
    Michal Hocko <mhocko@suse.com> writes:

    > On Thu 20-08-20 08:56:53, Suren Baghdasaryan wrote:
    > [...]
    >> Catching up on the discussion which was going on while I was asleep...
    >> So it sounds like there is a consensus that oom_adj should be moved to
    >> mm_struct rather than trying to synchronize it among tasks sharing mm.
    >> That sounds reasonable to me too. Michal answered all the earlier
    >> questions about this patch, so I won't be reiterating them, thanks
    >> Michal. If any questions are still lingering about the original patch
    >> I'll be glad to answer them.
    >
    > I think it still makes some sense to go with a simpler (aka less tricky)
    > solution which would be your original patch with an incremental fix for
    > vfork and the proper ordering (http://lkml.kernel.org/r/20200820124109.GI5033@dhcp22.suse.cz)
    > and then make a more complex shift to mm struct on top of that. The
    > former will be less tricky to backport to stable IMHO.

    So I am confused.

    I don't know how a subtle dependency on something in clone
    is better than something flat footed in exec.


    That said if we are going for a small change why not:

    /*
    * Make sure we will check other processes sharing the mm if this is
    * not vfrok which wants its own oom_score_adj.
    * pin the mm so it doesn't go away and get reused after task_unlock
    */
    if (!task->vfork_done) {
    struct task_struct *p = find_lock_task_mm(task);

    if (p) {
    - if (atomic_read(&p->mm->mm_users) > 1) {
    + if (atomic_read(&p->mm->mm_users) > p->signal->nr_threads) {
    mm = p->mm;
    mmgrab(mm);
    }
    task_unlock(p);
    }
    }

    That would seem to be the minimal change to make this happen. That has
    the advantage that if a processes does vfork it won't always have to
    take the slow path.

    Moving to the mm_struct is much less racy but this is simple.

    Eric

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