On Tue, 3 Jan 2023 09:58:36 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
>
>
> On 2022/12/31 5:45, Andrew Morton wrote:
> > On Fri, 30 Dec 2022 17:30:20 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> 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.
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?
