On 10/26/2010 03:18 PM, Jeremy Fitzhardinge wrote:
quoted text
>  We're seeing problems under Xen where large portions of the memory
> could be reserved (because they're not yet physically present, even
> though the appear in E820), and the 'start' and 'end' early_node_mem()
> is choosing is entirely within that reserved range.
> 
> Also, the code seems dubious because it adjusts start and end without
> regarding how much space it is trying to allocate:
> 
> 	/* extend the search scope */
> 	end = max_pfn_mapped << PAGE_SHIFT;
> 	if (end > (MAX_DMA32_PFN<<PAGE_SHIFT))
> 		start = MAX_DMA32_PFN<<PAGE_SHIFT;
> 	else
> 		start = MAX_DMA_PFN<<PAGE_SHIFT;
> 
> what if max_pfn_mapped is only a few pages larger than MAX_DMA32_PFN,
> and that is smaller than the size it is trying to allocate?
> 
> I tried just removing the start and end adjustments in early_node_mem()
> and the kernel booted fine under Xen, but it seemed to allocate at a
> very low address.  Should the for_each_active_range_index_in_nid() loop
> in find_memory_core_early() be iterating from high to low addresses?  If
> the allocation could be relied on to be top-down, then you wouldn't need
> to adjust start at all, and it would return the highest available memory
> in a natural way.

please check

[PATCH] x86, memblock: Fix early_node_mem with big reserved region.

Jeremy said Xen could reserve huge mem but still show as ram in e820.

early_node_mem could not find range because of start/end adjusting.

Let's use memblock_find_in_range instead ***_node. So get real top down in fallback path.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

diff --git a/arch/x86/mm/numa_64.c b/arch/x86/mm/numa_64.c
index 60f4985..7ffc9b7 100644
--- a/arch/x86/mm/numa_64.c
+++ b/arch/x86/mm/numa_64.c
@@ -178,11 +178,8 @@ static void * __init early_node_mem(int nodeid, unsigned long start,
 
 	/* extend the search scope */
 	end = max_pfn_mapped << PAGE_SHIFT;
-	if (end > (MAX_DMA32_PFN<<PAGE_SHIFT))
-		start = MAX_DMA32_PFN<<PAGE_SHIFT;
-	else
-		start = MAX_DMA_PFN<<PAGE_SHIFT;
-	mem = memblock_x86_find_in_range_node(nodeid, start, end, size, align);
+	start = MAX_DMA_PFN << PAGE_SHIFT;
+	mem = memblock_find_in_range(start, end, size, align);
 	if (mem != MEMBLOCK_ERROR)
 		return __va(mem);
 
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