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Subject: Re: a question of split_huge_page
To:     =?UTF-8?Q?Mika_Penttil=c3=a4?= <mika.penttila@nextfour.com>,
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        Hugh Dickins <hughd@google.com>
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From:   Alex Shi <alex.shi@linux.alibaba.com>
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在 2020/7/10 下午1:28, Mika Penttilä 写道:
>> Thanks a lot for quick reply!
>> What I am confusing is the call chain: __iommu_dma_alloc_pages()
>> to split_huge_page(), in the func, splited page,
>> 	page = alloc_pages_node(nid, alloc_flags, order);
>> And if the pages were added into lru, they maybe reclaimed and lost,
>> that would be a panic bug. But in fact, this never happened for long time.
>> Also I put a BUG() at the line, it's nevre triggered in ltp, and run_vmtests
> 
> In  __iommu_dma_alloc_pages, after split_huge_page(),  who is taking a
> reference on tail pages? Seems tail pages are freed and the function
> errornously returns them in pages[] array for use?
> 

Why you say so? It looks like the tail page returned and be used
	pages = __iommu_dma_alloc_pages() in iommu_dma_alloc_remap()
and still on node's lru. Is this right?

thanks!