[RFC V2 03/12] mm: Change generic FALLBACK zonelist creation process

[Anshuman Khandual]

Kernel allocation to CDM node has already been prevented by putting it's
entire memory in ZONE_MOVABLE. But the CDM nodes must also be isolated
from implicit allocations happening on the system.

Any isolation seeking CDM node requires isolation from implicit memory
allocations from user space but at the same time there should also have
an explicit way to do the memory allocation.

Platform node's both zonelists are fundamental to where the memory comes
from when there is an allocation request. In order to achieve these two
objectives as stated above, zonelists building process has to change as
both zonelists (i.e FALLBACK and NOFALLBACK) gives access to the node's
memory zones during any kind of memory allocation. The following changes
are implemented in this regard.

* CDM node's zones are not part of any other node's FALLBACK zonelist
* CDM node's FALLBACK list contains it's own memory zones followed by
  all system RAM zones in regular order as before
* CDM node's zones are part of it's own NOFALLBACK zonelist

These above changes ensure the following which in turn isolates the CDM
nodes as desired.

* There wont be any implicit memory allocation ending up in the CDM node
* Only __GFP_THISNODE marked allocations will come from the CDM node
* CDM node memory can be allocated through mbind(MPOL_BIND) interface
* System RAM memory will be used as fallback option in regular order in
  case the CDM memory is insufficient during targted allocation request

Sample zonelist configuration:

[NODE (0)]						RAM
        ZONELIST_FALLBACK (0xc00000000140da00)
                (0) (node 0) (DMA     0xc00000000140c000)
                (1) (node 1) (DMA     0xc000000100000000)
        ZONELIST_NOFALLBACK (0xc000000001411a10)
                (0) (node 0) (DMA     0xc00000000140c000)
[NODE (1)]						RAM
        ZONELIST_FALLBACK (0xc000000100001a00)
                (0) (node 1) (DMA     0xc000000100000000)
                (1) (node 0) (DMA     0xc00000000140c000)
        ZONELIST_NOFALLBACK (0xc000000100005a10)
                (0) (node 1) (DMA     0xc000000100000000)
[NODE (2)]						CDM
        ZONELIST_FALLBACK (0xc000000001427700)
                (0) (node 2) (Movable 0xc000000001427080)
                (1) (node 0) (DMA     0xc00000000140c000)
                (2) (node 1) (DMA     0xc000000100000000)
        ZONELIST_NOFALLBACK (0xc00000000142b710)
                (0) (node 2) (Movable 0xc000000001427080)
[NODE (3)]						CDM
        ZONELIST_FALLBACK (0xc000000001431400)
                (0) (node 3) (Movable 0xc000000001430d80)
                (1) (node 0) (DMA     0xc00000000140c000)
                (2) (node 1) (DMA     0xc000000100000000)
        ZONELIST_NOFALLBACK (0xc000000001435410)
                (0) (node 3) (Movable 0xc000000001430d80)
[NODE (4)]						CDM
        ZONELIST_FALLBACK (0xc00000000143b100)
                (0) (node 4) (Movable 0xc00000000143aa80)
                (1) (node 0) (DMA     0xc00000000140c000)
                (2) (node 1) (DMA     0xc000000100000000)
        ZONELIST_NOFALLBACK (0xc00000000143f110)
                (0) (node 4) (Movable 0xc00000000143aa80)

Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
---
 mm/page_alloc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f3e0c69..5db353a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4825,6 +4825,16 @@ static void build_zonelists(pg_data_t *pgdat)
 	i = 0;
 
 	while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {
+#ifdef CONFIG_COHERENT_DEVICE
+		/*
+		 * CDM node's own zones should not be part of any other
+		 * node's fallback zonelist but only it's own fallback
+		 * zonelist.
+		 */
+		if (is_cdm_node(node) && (pgdat->node_id != node))
+			continue;
+#endif
+
 		/*
 		 * We don't want to pressure a particular node.
 		 * So adding penalty to the first node in same
-- 
2.9.3