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From:   Zi Yan <ziy@nvidia.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Yang Shi <shy828301@gmail.com>, Yu Zhao <yuzhao@google.com>,
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        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Ryan Roberts <ryan.roberts@arm.com>,
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        linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 0/7] Split a folio to any lower order folios
Date:   Mon, 17 Apr 2023 15:26:58 -0400
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On 17 Apr 2023, at 10:20, David Hildenbrand wrote:

> On 16.04.23 20:11, Hugh Dickins wrote:
>> On Tue, 4 Apr 2023, Andrew Morton wrote:
>>> On Mon,  3 Apr 2023 16:18:32 -0400 Zi Yan <zi.yan@sent.com> wrote:
>>>
>>>> File folio supports any order and people would like to support flexi=
ble orders
>>>> for anonymous folio[1] too. Currently, split_huge_page() only splits=
 a huge
>>>> page to order-0 pages, but splitting to orders higher than 0 is also=
 useful.
>>>> This patchset adds support for splitting a huge page to any lower or=
der pages
>>>> and uses it during file folio truncate operations.
>>>
>>> This series (and its v1 & v2) don't appear to have much in the way of=

>>> detailed review.  As it's at v3 and has been fairly stable I'll queue=

>>> it up for some testing now, but I do ask that some reviewers go throu=
gh
>>> it please.
>>
>> Andrew, please don't let this series drift into 6.4-rc1.
>>
>> I've seen a bug or two (I'll point out in response to those patches),
>> but overall I don't see what the justification for the series is: done=

>> because it could be done, it seems to me, but liable to add surprises.=

>>
>> The cover letter says "splitting to orders higher than 0 is also usefu=
l",
>> but it's not clear why; and the infrastructure provided seems unsuited=

>> to the one use provided - I'll say more on that truncation patch.
>
> I agree. Maybe this patch set is something we want to have in the futur=
e once actual consumers that can benefit are in place, such that we can s=
how actual performance numbers with/without.

Ryan is working on large folio for anonymous pages and has shown promisin=
g performance
results[1]. This patchset would avoid getting base pages during split if =
possible.

>
> Until then, "365 insertions(+), 68 deletions(-)" certainly needs some r=
easonable motivation.

Come on. 225 out of 365 insertions are self tests code. We need motivatio=
n to add
testing code?

[1] https://lore.kernel.org/linux-mm/20230414130303.2345383-1-ryan.robert=
s@arm.com/

--
Best Regards,
Yan, Zi

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