On Wed, Oct 31, 2012 at 11:54:07AM -0700, David Rientjes wrote:
> On Wed, 31 Oct 2012, Minchan Kim wrote:
>
> > It sounds right in your kernel but principal problem is min_filelist_kbytes patch.
> > If normal exited process in exit path requires a page and there is no free page
> > any more, it ends up going to OOM path after try to reclaim memory several time.
> > Then,
> > In select_bad_process,
> >
> > if (task->flags & PF_EXITING) {
> > if (task == current) <== true
> > return OOM_SCAN_SELECT;
> > In oom_kill_process,
> >
> > if (p->flags & PF_EXITING)
> > set_tsk_thread_flag(p, TIF_MEMDIE);
> >
> > At last, normal exited process would get a free page.
> >
>
> select_bad_process() won't actually select the process for oom kill,
> though, if there are other PF_EXITING threads other than current. So if
> multiple threads are page faulting on tsk->robust_list, then no thread
> ends up getting killed. The temporary workaround would be to do a kill -9
> so that the logic in out_of_memory() could immediately give such threads
> access to memory reserves so the page fault will succeed. The real fix
It's not true any more.
3.6 includes following code in try_to_free_pages
/*
* Do not enter reclaim if fatal signal is pending. 1 is returned so
* that the page allocator does not consider triggering OOM
*/
if (fatal_signal_pending(current))
return 1;
So the hunged task never go to the OOM path and could be looping forever.
> would be to audit all possible cases in between setting
> tsk->flags |= PF_EXITING and tsk->mm = NULL that could cause a memory
> allocation and make exemptions for them in oom_scan_process_thread().
>
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--
Kind regards,
Minchan Kim
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