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SubjectRe: early_node_mem()'s memory allocation policy
On Tue, Oct 26, 2010 at 10:49:33PM -0700, Yinghai Lu wrote:
> On 10/26/2010 03:18 PM, Jeremy Fitzhardinge wrote:
> > 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

It definitly gets us across that hump. Thanks.
>
> [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>

Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

>
> 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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