[Xen-devel] [PATCH v1] mm/page_alloc: fix MEMF_no_dma allocations for single NUMA

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

Currently dma_bitsize is zero by default on single NUMA node machines.
This makes all alloc_domheap_pages() calls with MEMF_no_dma return NULL.

There is only 1 user of MEMF_no_dma: dom0_memflags, which are used
during memory allocation for Dom0. Failing allocation with default
dom0_memflags is especially severe for the PV Dom0 case: it makes
alloc_chunk() to use suboptimal 2MB allocation algorithm with a search
for higher memory addresses.

This can lead to the NMI watchdog timeout during PV Dom0 construction
on some machines, which can be worked around by specifying "dma_bits"
in Xen's cmdline manually.

Fix the issue by initialising dma_bitsize even on single NUMA machines.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/common/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index e591601f9c..4515282c27 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1863,7 +1863,7 @@ void __init end_boot_allocator(void)
     nr_bootmem_regions = 0;
     init_heap_pages(virt_to_page(bootmem_region_list), 1);
 
-    if ( !dma_bitsize && (num_online_nodes() > 1) )
+    if ( !dma_bitsize )
         dma_bitsize = arch_get_dma_bitsize();
 
     printk("Domain heap initialised");
-- 
2.17.1


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