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From:   "Zi Yan" <ziy@nvidia.com>
To:     "Yang Shi" <shy828301@gmail.com>
Cc:     "Linux MM" <linux-mm@kvack.org>,
        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
        linux-kselftest@vger.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        "Andrew Morton" <akpm@linux-foundation.org>,
        "Shuah Khan" <shuah@kernel.org>,
        "John Hubbard" <jhubbard@nvidia.com>,
        "Sandipan Das" <sandipan@linux.ibm.com>,
        "David Hildenbrand" <david@redhat.com>,
        "Mika Penttila" <mika.penttila@nextfour.com>
Subject: Re: [PATCH v2] mm: huge_memory: a new debugfs interface for splitting
 THP tests.
Date:   Thu, 11 Mar 2021 10:52:25 -0500
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On 10 Mar 2021, at 20:12, Yang Shi wrote:

> On Wed, Mar 10, 2021 at 7:36 AM Zi Yan <zi.yan@sent.com> wrote:
>>
>> From: Zi Yan <ziy@nvidia.com>
>>
>> We do not have a direct user interface of splitting the compound page
>> backing a THP and there is no need unless we want to expose the THP
>> implementation details to users. Adding an interface for debugging.
>>
>> By writing "<pid>,<vaddr_start>,<vaddr_end>" to
>> <debugfs>/split_huge_pages_in_range_pid, THPs within the given virtual=

>
> Can we reuse the existing split_huge_page knob instead of creating a ne=
w one?
>
> Two knobs for splitting huge pages on debugging purpose seem
> overkilling to me IMHO. I'm wondering if we could check if a special
> value (e.g. 1 or -1) is written then split all THPs as split_huge_page
> knob does?
>
> I don't think this interface is used widely so the risk should be very
> low for breaking userspace.

Thanks for the suggestion.

I prefer a separate interface to keep input handling simpler. I am also
planning to enhance this interface later to enable splitting huge pages
to any lower order when Matthew Wilcox=E2=80=99s large page in page cache=
 gets in,
so it is better to keep it separate from existing split_huge_pages.

=E2=80=94
Best Regards,
Yan Zi

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