linux-kernel - Re: [PATCH v3 4/6] mm: Introduce a pageflag for partially mapped folios

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Message-ID: <CAOUHufa=KgKvd4+w_fFqCBDSi-nG638PW01KairXcn50VQ4x7w@mail.gmail.com>
Date: Thu, 15 Aug 2024 20:50:28 -0600
From: Yu Zhao <yuzhao@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Usama Arif <usamaarif642@...il.com>, Barry Song <21cnbao@...il.com>, baohua@...nel.org, 
	cerasuolodomenico@...il.com, corbet@....net, david@...hat.com, 
	hannes@...xchg.org, kernel-team@...a.com, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, riel@...riel.com, 
	roman.gushchin@...ux.dev, rppt@...nel.org, ryan.roberts@....com, 
	shakeel.butt@...ux.dev, willy@...radead.org
Subject: Re: [PATCH v3 4/6] mm: Introduce a pageflag for partially mapped folios

On Thu, Aug 15, 2024 at 5:30 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Thu, 15 Aug 2024 16:25:09 +0100 Usama Arif <usamaarif642@...il.com> wrote:
>
> >
> >
> > commit c627655548fa09b59849e942da4decc84fa0b0f2
> > Author: Usama Arif <usamaarif642@...il.com>
> > Date:   Thu Aug 15 16:07:20 2024 +0100
> >
> >     mm: Introduce a pageflag for partially mapped folios fix
> >
> >     Fixes the original commit by not clearing partially mapped bit
> >     in hugeTLB folios and fixing deferred split THP stats.
> >
> > ...
> >
>
> Life is getting complicated.
>
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1758,7 +1758,6 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
> >                 free_gigantic_folio(folio, huge_page_order(h));
> >         } else {
> >                 INIT_LIST_HEAD(&folio->_deferred_list);
> > -               folio_clear_partially_mapped(folio);
> >                 folio_put(folio);
> >         }
> >  }
>
> Yu Zhao's "mm/hugetlb: use __GFP_COMP for gigantic folios" was
> expecting that folio_clear_partially_mapped() to be there.
>
> I resolved this within
> mm-hugetlb-use-__gfp_comp-for-gigantic-folios.patch thusly:
>
> @@ -1748,18 +1704,8 @@ static void __update_and_free_hugetlb_fo
>
>         folio_ref_unfreeze(folio, 1);
>
> -       /*
> -        * Non-gigantic pages demoted from CMA allocated gigantic pages
> -        * need to be given back to CMA in free_gigantic_folio.
> -        */
> -       if (hstate_is_gigantic(h) ||
> -           hugetlb_cma_folio(folio, huge_page_order(h))) {
> -               destroy_compound_gigantic_folio(folio, huge_page_order(h));
> -               free_gigantic_folio(folio, huge_page_order(h));
> -       } else {
> -               INIT_LIST_HEAD(&folio->_deferred_list);
> -               folio_put(folio);
> -       }
> +       INIT_LIST_HEAD(&folio->_deferred_list);
> +       hugetlb_free_folio(folio);
>  }
>
>  /*
>
> Please check.

Confirmed, thanks.