Re: [patch -mmotm] mm: invoke oom killer for __GFP_NOFAIL

[Minchan Kim <minchan.kim@gmail.com>]

Hi, Mel.

On Mon, May 11, 2009 at 10:38 PM, Mel Gorman <mel@csn.ul.ie> wrote:
> On Mon, May 11, 2009 at 08:21:21PM +0900, Minchan Kim wrote:
>> On Mon, May 11, 2009 at 6:12 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
>> > On Mon, May 11, 2009 at 5:40 PM, David Rientjes <rientjes@google.com> wrote:
>> >> On Mon, 11 May 2009, Minchan Kim wrote:
>> >>
>> >>> Hmm.. if __alloc_pages_may_oom fail to allocate free page due to order > PAGE_ALLOC_COSTRY_ORDER,
>> >>>
>> >>> It will go to nopage label in __alloc_pages_slowpath.
>> >>> Then it will show the page allocation failure warning and will return.
>> >>> Retrying depends on caller.
>> >>>
>> >>
>> >> Correct.
>> >>
>> >>> So, I think it won't loop forever.
>> >>> Do I miss something ?
>> >>>
>> >>
>> >> __GFP_NOFAIL allocations shouldn't fail, that's the point of the gfp flag.
>> >> So failing without attempting to free some memory is the wrong thing to
>> >> do.
>> >
>> > Thanks for quick reply.
>> > I was confused by your description.
>> > I thought you suggested we have to prevent loop forever.
>> >
>> >>
>> >>> In addition, the OOM killer can help for getting the high order pages ?
>> >>>
>> >>
>> >> Sure, if it selects a task that will free a lot of memory, which is it's
>> >> goal.
>> >>
>> >
>> > How do we know any task have a lot of memory ?
>> > If we select wrong task and kill one ?
>> >
>> > I have a concern about innocent task.
>>
>> Now, I look over __out_of_memory.
>> For selecting better tasks in case of PAGE_ALLOC_COSTRY_ORDER, How
>> about increasing score of task which have VM_HUGETLB vma in badness ?
>>
>
> That is unjustified. It penalises a process even if it only allocated one
> hugepage and it is not a reflection of how much memory the process is using
> or how badly behaved it is.
> Even worse, if the huge page was allocated from the static hugepage pool then
> the hugepages are freed to the hugepage pool and not the page allocator when
> the process is killed. This means that killing a process using hugepages
> does not necessarily help applications requiring more memory unless they
> also want hugepages. However, a hugepage allocation will not trigger the
> OOM killer so killing processes using hugepages still does not help.

Thanks for pointing me.
In fact, I expect your great answer. :)

So, how do we prevent innocent task killing for allocation of high order page ?
I think it is trade off. but at least, we have been prevent it until now.

But this patch increases the probability of innocent task killing.
Is GFP_NOFAIL's early bailout more important than killing of innocent task ?

I am not sure.

> --
> Mel Gorman
> Part-time Phd Student                          Linux Technology Center
> University of Limerick                         IBM Dublin Software Lab
>



-- 
Kinds regards,
Minchan Kim