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[Xen-devel] [PATCH] fix zone-over-node preference when allocating memory

When Xen allocates the guest's memory, it will try to use non-DMA-able zones first (probably because they are less precious). If there are no such pages available on a certain node, Xen will revert to allocating low pages from another node and thus ignoring the node-preference. This patch fixes this by first checking if non-DMA pages are available on a node and reverting to DMA-able pages if not. This fixes incorrect NUMA memory allocation on nodes with memory below the DMA border (4GB on x86-64, affects for instance dual-node machines with 4gig on each node).


P.S. This fix was already part of my NUMA guest patches back in August, this is just an extract of these.

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>

Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 277-84917
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AMD Saxony Limited Liability Company & Co. KG,
Wilschdorfer Landstr. 101, 01109 Dresden, Germany
Register Court Dresden: HRA 4896, General Partner authorized
to represent: AMD Saxony LLC (Wilmington, Delaware, US)
General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy
diff -r 1f4b29eaf7f4 xen/common/page_alloc.c
--- a/xen/common/page_alloc.c   Thu Dec 20 17:30:27 2007 +0000
+++ b/xen/common/page_alloc.c   Fri Dec 21 22:58:58 2007 +0100
@@ -797,7 +797,12 @@ struct page_info *__alloc_domheap_pages(
     if ( (zone_hi + PAGE_SHIFT) >= dma_bitsize )
-        pg = alloc_heap_pages(dma_bitsize - PAGE_SHIFT, zone_hi, cpu, order);
+        if (avail_heap_pages(dma_bitsize - PAGE_SHIFT, zone_hi,
+            cpu_to_node (cpu)) >= ( 1UL << order ))
+        {
+            pg = alloc_heap_pages(dma_bitsize - PAGE_SHIFT, zone_hi,
+                cpu, order);
+        }
         /* Failure? Then check if we can fall back to the DMA pool. */
         if ( unlikely(pg == NULL) &&
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