Re: [patch v2 3/3] mm: page_alloc: fair zone allocator policy

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Mon, Aug 05, 2013 at 01:34:23PM +0200, Andrea Arcangeli wrote:
>On Mon, Aug 05, 2013 at 06:34:56PM +0800, Wanpeng Li wrote:
>> Why round robin allocator don't consume ZONE_DMA?
>
>I guess lowmem reserve reserves it all, 4GB/256(ratio)=16MB.
>

Ah, lowmem reservation reserve all ZONE_DMA:

x86_64 4GB

protection: (0, 3251, 4009, 4009)

Thanks for pointing out. ;-)

>The only way to relax it would be 1) to account depending on memblock
>types and allow only the movable ones to bypass the lowmem reserve and
>prevent a change from movable type if lowmem reserve doesn't pass, 2)
>use memory migration to move the movable pages from the lower zones to
>the highest zone if reclaim fails if __GFP_DMA32 or __GFP_DMA is set,
>or highmem is missing on 32bit kernels. The last point involving
>memory migration would work similarly to compaction but it isn't black
>and white, and it would cost CPU as well. The memory used by the
>simple lowmem reserve mechanism is probably not significant enough to
>warrant such an effort.

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