On 11/28/2016 10:51 PM, Anshuman Khandual wrote:

On 11/29/2016 02:42 AM, Dave Hansen wrote:

quoted

quoted

On 11/22/2016 06:19 AM, Anshuman Khandual wrote:

quoted

quoted

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -3715,7 +3715,7 @@ struct page *
 		.migratetype = gfpflags_to_migratetype(gfp_mask),
 	};
 
-	if (cpusets_enabled()) {
+	if (cpusets_enabled() && !(alloc_mask & __GFP_THISNODE)) {
 		alloc_mask |= __GFP_HARDWALL;
 		alloc_flags |= ALLOC_CPUSET;
 		if (!ac.nodemask)

This means now that any __GFP_THISNODE allocation can "escape" the
cpuset.  That seems like a pretty major change to how cpusets works.  Do
we know that *ALL* __GFP_THISNODE allocations are truly lacking in a
cpuset context that can be enforced?

Right, I know its a very blunt change. With the cpuset based isolation
of coherent device node for the user space tasks leads to a side effect
that a driver or even kernel cannot allocate memory from the coherent

...

Well, we have __GFP_HARDWALL:

	 * __GFP_HARDWALL enforces the cpuset memory allocation policy.

which you can clear in the places where you want to do an allocation but
want to ignore cpusets.  But, __cpuset_node_allowed() looks like it gets
a little funky if you do that since it would probably be falling back to
the root cpuset that also would not have the new node in mems_allowed.

What exactly are the kernel-internal places that need to allocate from
the coherent device node?  When would this be done out of the context of
an application *asking* for memory in the new node?

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