On Wed, 6 Jun 2007, Peter Zijlstra wrote:
> > diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> > --- a/kernel/cpuset.c
> > +++ b/kernel/cpuset.c
> > @@ -2431,12 +2431,6 @@ int __cpuset_zone_allowed_softwall(struct zone *z,
> > gfp_t gfp_mask)
> > might_sleep_if(!(gfp_mask & __GFP_HARDWALL));
> > if (node_isset(node, current->mems_allowed))
> > return 1;
> > - /*
> > - * Allow tasks that have access to memory reserves because they have
> > - * been OOM killed to get memory anywhere.
> > - */
> > - if (unlikely(test_thread_flag(TIF_MEMDIE)))
> > - return 1;
> > if (gfp_mask & __GFP_HARDWALL) /* If hardwall request, stop here */
> > return 0;
> >
>
> This seems a little pointless, since cpuset_zone_allowed_softwall() is
> only effective with ALLOC_CPUSET, and the ALLOC_NO_WATERMARKS
> allocations opened up by TIF_MEMDIE don't use that.
>
That's the change. Memory reserves on a per-zone level would now be used
with respect to ALLOC_NO_WATERMARKS because TIF_MEMDIE tasks no longer
have an explicit bypass for them. If the node is not in the task's
mems_allowed and it's a __GFP_HARDWALL allocation or if it's neither
PF_EXITING or in the nearest_exclusive_ancestor() of that task's cpuset,
then we move on to the next zone in get_page_from_freelist().
The problem the patch addresses is that, as you mentioned, tasks with
TIF_MEMDIE have an explicit bypass over using any memory reserves and can
thus, depending on zonelist ordering, allocate first on nodes outside its
mems_allowed even in the case of an exclusive cpuset before exhausting its
own memory. That behavior is wrong.
David
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