lkml.org 
[lkml]   [2011]   [Aug]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] oom: skip frozen tasks
    On Fri, 26 Aug 2011, Michal Hocko wrote:

    > Let's give all frozen tasks a bonus (OOM_SCORE_ADJ_MAX/2) so that we do
    > not consider them unless really necessary and if we really pick up one
    > then thaw its threads before we try to kill it.
    >

    I don't like arbitrary heuristics like this because they polluted the old
    oom killer before it was rewritten and made it much more unpredictable.
    The only heuristic it includes right now is a bonus for root tasks so that
    when two processes have nearly the same amount of memory usage (within 3%
    of available memory), the non-root task is chosen instead.

    This bonus is actually saying that a single frozen task can use up to 50%
    more of the machine's capacity in a system-wide oom condition than the
    task that will now be killed instead. That seems excessive.

    I do like the idea of automatically thawing the task though and if that's
    possible then I don't think we need to manipulate the badness heuristic at
    all. I know that wouldn't be feasible when we've frozen _all_ threads and
    that's why we have oom_killer_disable(), but we'll have to check with
    Rafael to see if something like this could work. Rafael?

    > TODO
    > - given bonus might be too big?
    > - aren't we racing with try_to_freeze_tasks?
    > ---
    > mm/oom_kill.c | 13 +++++++++++++
    > 1 files changed, 13 insertions(+), 0 deletions(-)
    >
    > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    > index 626303b..fd194bc 100644
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -32,6 +32,7 @@
    > #include <linux/mempolicy.h>
    > #include <linux/security.h>
    > #include <linux/ptrace.h>
    > +#include <linux/freezer.h>
    >
    > int sysctl_panic_on_oom;
    > int sysctl_oom_kill_allocating_task;
    > @@ -214,6 +215,14 @@ unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
    > points += p->signal->oom_score_adj;
    >
    > /*
    > + * Do not try to kill frozen tasks unless there is nothing else to kill.
    > + * We do not want to give it 1 point because we still want to select a good
    > + * candidate among all frozen tasks. Let's give it a reasonable bonus.
    > + */
    > + if (frozen(p))
    > + points -= OOM_SCORE_ADJ_MAX/2;
    > +
    > + /*
    > * Never return 0 for an eligible task that may be killed since it's
    > * possible that no single user task uses more than 0.1% of memory and
    > * no single admin tasks uses more than 3.0%.
    > @@ -450,6 +459,10 @@ static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
    > pr_err("Kill process %d (%s) sharing same memory\n",
    > task_pid_nr(q), q->comm);
    > task_unlock(q);
    > +
    > + if (frozen(q))
    > + thaw_process(q);
    > +
    > force_sig(SIGKILL, q);
    > }
    >


    \
     
     \ /
      Last update: 2011-08-26 11:23    [W:0.043 / U:0.244 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site