Re: [PATCH v4 0/4] Make alloc_contig_range handle Hugetlb pages

[David Hildenbrand]

On 17.03.21 11:05, Oscar Salvador wrote:
> On Wed, Mar 17, 2021 at 10:48:31AM +0100, David Hildenbrand wrote:
> > > I was preparing v5, and I wanted to be sure I understood you here.
> > >
> > > Right you are that the in-use page check can be dropped, as those pages
> > > can
> > > be migrated away, and the Hugetlb page check can also be dropped since
> > > isolate_migratepages_range is now capable of dealing with those kind of
> > > pages.
> > >
> > > > b) Similarly, check for gigantic pages and/or movability/migratability.
> > >
> > > I lost you here.
> > >
> > > isolate_or_dissolve_huge_page() already bails out on hugetlb-gigantic
> > > pages.
> > >
> > > Or do you mean to place an upfront check here? (hstate_is_gigantic())?
> >
> > Yes. But I prefer a) and keeping it simple here -- just doing basic sanity
> > checks (online, zone, PageReserved()) that are absolutely necessary.
>
> Ok, I am probably dense as I understood as if you were lean towards having
> a) + b).

Sorry, I meant either a) or b) :)

> That is what I have as the last patch of the patchset:
>
>  From e97175b7d4970cbdcbafcf8c398f72a571e817b0 Mon Sep 17 00:00:00 2001
> From: Oscar Salvador <osalvador@xxxxxxx>
> Date: Thu, 18 Mar 2021 05:03:18 +0100
> Subject: [PATCH] mm,page_alloc: Drop unnecesary checks from
>   pfn_range_valid_contig
>
> pfn_range_valid_contig() bails out when it finds an in-use page or a
> hugetlb page, among other things.
> We can drop the in-use page check since __alloc_contig_pages can migrate
> away those pages, and the hugetlb page check can go too since
> isolate_migratepages_range is now capable of dealing with hugetlb pages.

Might want to mention that the existing checks were racy either way :)

> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
> ---
>   mm/page_alloc.c | 6 ------
>   1 file changed, 6 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4cb455355f6d..50d73e68b79e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8685,12 +8685,6 @@ static bool pfn_range_valid_contig(struct zone *z, unsigned long start_pfn,
>
>                  if (PageReserved(page))
>                          return false;
> -
> -               if (page_count(page) > 0)
> -                       return false;
> -
> -               if (PageHuge(page))
> -                       return false;
>          }
>          return true;
>   }


--
Thanks,

David / dhildenb