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From:   Zi Yan <ziy@nvidia.com>
To:     Matthew Wilcox <willy@infradead.org>
CC:     Roman Gushchin <guro@fb.com>, <linux-mm@kvack.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
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Subject: Re: [RFC PATCH 3/6] mm: page_owner: add support for splitting to any
 order in split page_owner.
Date:   Tue, 17 Nov 2020 16:12:03 -0500
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On 17 Nov 2020, at 16:05, Matthew Wilcox wrote:

> On Fri, Nov 13, 2020 at 05:38:01PM -0800, Roman Gushchin wrote:
>> On Fri, Nov 13, 2020 at 08:08:58PM -0500, Zi Yan wrote:
>>> Matthew recently converted split_page_owner to take nr instead of ord=
er.[1]
>>> But I am not
>>> sure why, since it seems to me that two call sites (__split_huge_page=
 in
>>> mm/huge_memory.c and split_page in mm/page_alloc.c) can pass the orde=
r
>>> information.
>>
>> Yeah, I'm not sure why too. Maybe Matthew has some input here?
>> You can also pass new_nr, but IMO orders look so much better here.
>
> If only I'd written that information in the changelog ... oh wait, I di=
d!
>
>     mm/page_owner: change split_page_owner to take a count
>
>     The implementation of split_page_owner() prefers a count rather tha=
n the
>     old order of the page.  When we support a variable size THP, we won=
't
>     have the order at this point, but we will have the number of pages.=

>     So change the interface to what the caller and callee would prefer.=


There are two callers, split_page in mm/page_alloc.c and __split_huge_pag=
e in
mm/huge_memory.c. The former has the page order. The latter has the page =
order
information before __split_huge_page_tail is called, so we can do
old_order =3D thp_order(head) instead of nr =3D thp_nr_page(head) and use=
 old_order.
What am I missing there?

Thanks.

=E2=80=94
Best Regards,
Yan Zi

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