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SubjectRe: [PATCH v2] mm: huge_memory: convert split_huge_pages_all() to use a folio
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On 2023/1/6 11:06, Andrew Morton wrote:
> On Tue, 3 Jan 2023 09:58:36 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
>
>>
>>
>> On 2022/12/31 5:45, Andrew Morton wrote:
>>> On Fri, 30 Dec 2022 17:30:20 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
>>>
>>>> Straightforwardly convert split_huge_pages_all() to use a folio.
>>>>
>>>> ...
>>>>
>>>> --- a/mm/huge_memory.c
>>>> +++ b/mm/huge_memory.c
>>>> @@ -2932,6 +2932,7 @@ static void split_huge_pages_all(void)
>>>> {
>>>> struct zone *zone;
>>>> struct page *page;
>>>> + struct folio *folio;
>>>> unsigned long pfn, max_zone_pfn;
>>>> unsigned long total = 0, split = 0;
>>>>
>>>> @@ -2944,24 +2945,32 @@ static void split_huge_pages_all(void)
>>>> int nr_pages;
>>>>
>>>> page = pfn_to_online_page(pfn);
>>>> - if (!page || !get_page_unless_zero(page))
>>>> + if (!page || PageTail(page))
>>>> + continue;
>>>> + folio = page_folio(page);
>>>> + if (!folio_try_get(folio))
>>>> continue;
>>>>
>>>> - if (zone != page_zone(page))
>>>> + if (unlikely(page_folio(page) != folio))
>>>> + goto next;
>>>> +
>>>> + if (zone != folio_zone(folio))
>>>> goto next;
>>>
>>> I'm still not understanding the above hunk. Why is the
>>> "page_folio(page) != folio" check added? Should it be commented?
>>
>> There is a comment in try_get_folio(), is it enough?
>
> Nobody would think to look at a private function in gup.c.

Sorry,I mean that comment is to explain why adding a new recheck.

>
> I suggest this folio_try_get() rule be documented at the
> folio_try_get() implementation site.
>
> Most callers do perform this check, but not the ones in vmscan.c ?

Hope Matthew could give some advise, thanks

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