Re: [PATCH v3] mm: huge_memory: a new debugfs interface for splitting THP tests.

["Zi Yan" <ziy@nvidia.com>]

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On 15 Mar 2021, at 8:07, Kirill A. Shutemov wrote:

> On Thu, Mar 11, 2021 at 07:57:12PM -0500, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>>
>> We do not have a direct user interface of splitting the compound page
>> backing a THP
>
> But we do. You expand it.
>
>> and there is no need unless we want to expose the THP
>> implementation details to users. Make <debugfs>/split_huge_pages accept
>> a new command to do that.
>>
>> By writing "<pid>,<vaddr_start>,<vaddr_end>" to
>> <debugfs>/split_huge_pages, THPs within the given virtual address range
>> from the process with the given pid are split. It is used to test
>> split_huge_page function. In addition, a selftest program is added to
>> tools/testing/selftests/vm to utilize the interface by splitting
>> PMD THPs and PTE-mapped THPs.
>>
>
> Okay, makes sense.
>
> But it doesn't cover non-mapped THPs. tmpfs may have file backed by THP
> that mapped nowhere. Do we want to cover this case too?

Sure. It would be useful when large page in page cache too. I will send
v4 with tmpfs THP split. I will definitely need a review for it, since
I am not familiar with getting a page from a file path.

> Maybe have PID:<pid>,<vaddr_start>,<vaddr_end> and
> FILE:<path>,<off_start>,<off_end> ?

Or just check input[0] == ‘/‘ for file path input.


—
Best Regards,
Yan Zi

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