Re: a question of split_huge_page

[Mika PenttilÃ]

On 10.7.2020 10.00, Alex Shi wrote:
>
> å 2020/7/10 äå1:28, Mika Penttilà åé:
>>> 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!
IMHO they are new pages coming from alloc_pages_node() so they are not
on lru. And split_huge_page() frees not pinned tail pages again to page
allocator.

Thanks,
Mika

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