On Wed, 2 Jun 2010, KOSAKI Motohiro wrote:
> > > @@ -291,9 +309,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
> > > * Otherwise we could get an easy OOM deadlock.
> > > */
> > > if (p->flags & PF_EXITING) {
> > > - if (p != current)
> > > + if (p != current) {
> > > + boost_dying_task_prio(p, mem);
> > > return ERR_PTR(-1UL);
> > > -
> > > + }
> > > chosen = p;
> > > *ppoints = ULONG_MAX;
> > > }
> >
> > This has the potential to actually make it harder to free memory if p is
> > waiting to acquire a writelock on mm->mmap_sem in the exit path while the
> > thread holding mm->mmap_sem is trying to run.
>
> if p is waiting, changing prio have no effect. It continue tol wait to release mmap_sem.
>
And that can reduce the runtime of the thread holding a writelock on
mm->mmap_sem, making the exit actually take longer than without the patch
if its priority is significantly higher, especially on smaller machines.
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