linux-kernel - Re: [PATCH -mm] Kill existing current task quickly

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Date:	Wed, 17 Feb 2010 19:55:14 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH -mm] Kill existing current task quickly

On Wed, 2010-02-17 at 01:36 -0800, David Rientjes wrote:
> On Wed, 17 Feb 2010, Minchan Kim wrote:
> 
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 3618be3..d5e3d70 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -32,6 +32,8 @@ int sysctl_panic_on_oom;
> >  int sysctl_oom_kill_allocating_task;
> >  int sysctl_oom_dump_tasks;
> >  static DEFINE_SPINLOCK(zone_scan_lock);
> > +
> > +unsigned int nr_memdie; /* count of TIF_MEMDIE processes */
> >  /* #define DEBUG */
> > 
> >  /*
> > @@ -295,6 +297,8 @@ static struct task_struct
> > *select_bad_process(unsigned long *ppoints,
> > 
> >                         chosen = p;
> >                         *ppoints = ULONG_MAX;
> > +                       if (nr_memdie == 0)
> > +                               break;
> >                 }
> > 
> >                 if (p->signal->oom_adj == OOM_DISABLE)
> 
> Nack, finding a candidate task with TIF_MEMDIE set is not the only time we 
> return ERR_PTR(-1UL) from select_bad_process(): we also do it if any other 
> task other than current is PF_EXITING.  Thus, we _must_ continue the 
> tasklist scan to avoid needlessly killing current simply because it was 
> the first PF_EXITING task in the tasklist.

Okay. Sorry for missing PF_EXITING tasks. 

> 
> > @@ -403,8 +407,6 @@ static void __oom_kill_task(struct task_struct *p,
> > int verbose)
> >                        K(p->mm->total_vm),
> >                        K(get_mm_counter(p->mm, MM_ANONPAGES)),
> >                        K(get_mm_counter(p->mm, MM_FILEPAGES)));
> > -       task_unlock(p);
> > -
> >         /*
> >          * We give our sacrificial lamb high priority and access to
> >          * all the memory it needs. That way it should be able to
> > @@ -412,7 +414,11 @@ static void __oom_kill_task(struct task_struct
> > *p, int verbose)
> >          */
> >         p->rt.time_slice = HZ;
> >         set_tsk_thread_flag(p, TIF_MEMDIE);
> > -
> > +       /*
> > +        * nr_memdie is protected by task_lock.
> > +        */
> > +       nr_memdie++;
> > +       task_unlock(p);
> >         force_sig(SIGKILL, p);
> >  }
> > 
> 
> task_lock() is a per-task entity, i.e. each task_struct has an alloc_lock 
> spinlock.  This cannot protect a global variable.

Yes. It was utterly dumb lock usage. 
Thanks for the quick reply. 
 

-- 
Kind regards,
Minchan Kim


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