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    SubjectRe: [patch 2/7 -mm] oom: sacrifice child with highest badness score for parent
    On Wed, 10 Feb 2010 08:32:10 -0800 (PST)
    David Rientjes <rientjes@google.com> wrote:

    > When a task is chosen for oom kill, the oom killer first attempts to
    > sacrifice a child not sharing its parent's memory instead.
    > Unfortunately, this often kills in a seemingly random fashion based on
    > the ordering of the selected task's child list. Additionally, it is not
    > guaranteed at all to free a large amount of memory that we need to
    > prevent additional oom killing in the very near future.
    >
    > Instead, we now only attempt to sacrifice the worst child not sharing its
    > parent's memory, if one exists. The worst child is indicated with the
    > highest badness() score. This serves two advantages: we kill a
    > memory-hogging task more often, and we allow the configurable
    > /proc/pid/oom_adj value to be considered as a factor in which child to
    > kill.
    >
    > Reviewers may observe that the previous implementation would iterate
    > through the children and attempt to kill each until one was successful
    > and then the parent if none were found while the new code simply kills
    > the most memory-hogging task or the parent. Note that the only time
    > oom_kill_task() fails, however, is when a child does not have an mm or
    > has a /proc/pid/oom_adj of OOM_DISABLE. badness() returns 0 for both
    > cases, so the final oom_kill_task() will always succeed.
    >
    > Signed-off-by: David Rientjes <rientjes@google.com>

    Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    Maybe better than current logic..but I'm not sure why we have to check children ;)

    BTW,
    ==
    list_for_each_entry(child, &p->children, sibling) {
    task_lock(child);
    if (child->mm != mm && child->mm)
    points += child->mm->total_vm/2 + 1;
    task_unlock(child);
    }
    ==
    I wonder this part should be
    points += (child->total_vm/2) >> child->signal->oom_adj + 1

    If not, in following situation,
    ==
    parent (oom_adj = 0)
    -> child (oom_adj=-15, very big memory user)
    ==
    the child may be killd at first, anyway. Today, I have to explain customers
    "When you set oom_adj to a process, please set the same value to all ancestors.
    Otherwise, your oom_adj value will be ignored."

    No ?

    Thanks,
    -Kame

    > ---
    > mm/oom_kill.c | 23 +++++++++++++++++------
    > 1 files changed, 17 insertions(+), 6 deletions(-)
    >
    > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -432,7 +432,10 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
    > unsigned long points, struct mem_cgroup *mem,
    > const char *message)
    > {
    > + struct task_struct *victim = p;
    > struct task_struct *c;
    > + unsigned long victim_points = 0;
    > + struct timespec uptime;
    >
    > if (printk_ratelimit())
    > dump_header(p, gfp_mask, order, mem);
    > @@ -446,17 +449,25 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
    > return 0;
    > }
    >
    > - printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
    > - message, task_pid_nr(p), p->comm, points);
    > + pr_err("%s: Kill process %d (%s) with score %lu or sacrifice child\n",
    > + message, task_pid_nr(p), p->comm, points);
    >
    > - /* Try to kill a child first */
    > + /* Try to sacrifice the worst child first */
    > + do_posix_clock_monotonic_gettime(&uptime);
    > list_for_each_entry(c, &p->children, sibling) {
    > + unsigned long cpoints;
    > +
    > if (c->mm == p->mm)
    > continue;
    > - if (!oom_kill_task(c))
    > - return 0;
    > +
    > + /* badness() returns 0 if the thread is unkillable */
    > + cpoints = badness(c, uptime.tv_sec);
    > + if (cpoints > victim_points) {
    > + victim = c;
    > + victim_points = cpoints;
    > + }
    > }
    > - return oom_kill_task(p);
    > + return oom_kill_task(victim);
    > }
    >
    > #ifdef CONFIG_CGROUP_MEM_RES_CTLR
    >



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