[PATCH 04/37] xen: introduce an arch helper for default dma zone status

[Wei Chen <wei.chen@xxxxxxx>]

In current code, when Xen is running in a multiple nodes NUMA
system, it will set dma_bitsize in end_boot_allocator to reserve
some low address memory for DMA.

There are some x86 implications in current implementation. Becuase
on x86, memory starts from 0. On a multiple nodes NUMA system, if
a single node contains the majority or all of the DMA memory. x86
prefer to give out memory from non-local allocations rather than
exhausting the DMA memory ranges. Hence x86 use dma_bitsize to set
aside some largely arbitrary amount memory for DMA memory ranges.
The allocations from these memory ranges would happen only after
exhausting all other nodes' memory.

But the implications are not shared across all architectures. For
example, Arm doesn't have these implications. So in this patch, we
introduce an arch_have_default_dmazone helper for arch to determine
that it need to set dma_bitsize for reserve DMA allocations or not.

Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
---
 xen/arch/x86/numa.c        | 5 +++++
 xen/common/page_alloc.c    | 2 +-
 xen/include/asm-arm/numa.h | 5 +++++
 xen/include/asm-x86/numa.h | 1 +
 4 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/numa.c b/xen/arch/x86/numa.c
index ce79ee44ce..1fabbe8281 100644
--- a/xen/arch/x86/numa.c
+++ b/xen/arch/x86/numa.c
@@ -371,6 +371,11 @@ unsigned int __init arch_get_dma_bitsize(void)
                  + PAGE_SHIFT, 32);
 }
 
+unsigned int arch_have_default_dmazone(void)
+{
+    return ( num_online_nodes() > 1 ) ? 1 : 0;
+}
+
 static void dump_numa(unsigned char key)
 {
     s_time_t now = NOW();
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 5801358b4b..80916205e5 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1889,7 +1889,7 @@ void __init end_boot_allocator(void)
     }
     nr_bootmem_regions = 0;
 
-    if ( !dma_bitsize && (num_online_nodes() > 1) )
+    if ( !dma_bitsize && arch_have_default_dmazone() )
         dma_bitsize = arch_get_dma_bitsize();
 
     printk("Domain heap initialised");
diff --git a/xen/include/asm-arm/numa.h b/xen/include/asm-arm/numa.h
index 31a6de4e23..9d5739542d 100644
--- a/xen/include/asm-arm/numa.h
+++ b/xen/include/asm-arm/numa.h
@@ -25,6 +25,11 @@ extern mfn_t first_valid_mfn;
 #define node_start_pfn(nid) (mfn_x(first_valid_mfn))
 #define __node_distance(a, b) (20)
 
+static inline unsigned int arch_have_default_dmazone(void)
+{
+    return 0;
+}
+
 #endif /* __ARCH_ARM_NUMA_H */
 /*
  * Local variables:
diff --git a/xen/include/asm-x86/numa.h b/xen/include/asm-x86/numa.h
index 3cf26c2def..8060cbf3f4 100644
--- a/xen/include/asm-x86/numa.h
+++ b/xen/include/asm-x86/numa.h
@@ -78,5 +78,6 @@ extern int valid_numa_range(u64 start, u64 end, nodeid_t 
node);
 void srat_parse_regions(u64 addr);
 extern u8 __node_distance(nodeid_t a, nodeid_t b);
 unsigned int arch_get_dma_bitsize(void);
+unsigned int arch_have_default_dmazone(void);
 
 #endif
-- 
2.25.1