On Tue, 2007-06-05 at 23:42 -0700, David Rientjes wrote:
> 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.
Right, I see your point; however considering that its a system
allocation, and all these constraints get violated by interrupts anyway,
its more of an application container than a strict allocation container.
Are you actually seeing the described behaviour, or just being pedantic
(nothing wrong with that per-se)?
I would actually be bold and make it worse by proposing something like
this, which has the benefit of making the reserve threshold system wide.
---
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1eef614..870a791 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1630,6 +1630,21 @@ rebalance:
&& !in_interrupt()) {
if (!(gfp_mask & __GFP_NOMEMALLOC)) {
nofail_alloc:
+ /*
+ * break out of mempolicy boundaries
+ */
+ zonelist = NODE_DATA(numa_node_id())->node_zonelists +
+ gfp_zone(gfp_mask);
+
+ /*
+ * Before going bare metal, try to get a page above the
+ * critical threshold - ignoring CPU sets.
+ */
+ page = get_page_from_freelist(gfp_mask, order, zonelist,
+ ALLOC_MIN|ALLOC_HIGH|ALLOC_HARDER);
+ if (page)
+ goto got_pg;
+
/* go through the zonelist yet again, ignoring mins */
page = get_page_from_freelist(gfp_mask, order,
zonelist, ALLOC_NO_WATERMARKS);
-
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