linux-kernel - Re: [PATCH v2] mm/shmem: fix THP allocation and fallback loop

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Message-ID: <CAGsJ_4zKcxO-Tacy0jCZSs83+fGsgqQYNib9nCXoLTuL+hdLxQ@mail.gmail.com>
Date: Thu, 23 Oct 2025 18:51:20 +1300
From: Barry Song <21cnbao@...il.com>
To: Kairui Song <ryncsn@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, Hugh Dickins <hughd@...gle.com>, 
	Dev Jain <dev.jain@....com>, David Hildenbrand <david@...hat.com>, 
	Liam Howlett <liam.howlett@...cle.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Mariano Pache <npache@...hat.com>, Matthew Wilcox <willy@...radead.org>, 
	Ryan Roberts <ryan.roberts@....com>, Zi Yan <ziy@...dia.com>, linux-kernel@...r.kernel.org, 
	Kairui Song <kasong@...cent.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] mm/shmem: fix THP allocation and fallback loop

>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index b50ce7dbc84a..7559773ebb30 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1895,10 +1895,11 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
>                 order = highest_order(suitable_orders);
>                 while (suitable_orders) {
>                         pages = 1UL << order;
> -                       index = round_down(index, pages);
> -                       folio = shmem_alloc_folio(gfp, order, info, index);
> -                       if (folio)
> +                       folio = shmem_alloc_folio(gfp, order, info, round_down(index, pages));
> +                       if (folio) {
> +                               index = round_down(index, pages);
>                                 goto allocated;
> +                       }

Could this be a temporary variable to store round_down(index, pages)?

>
>                         if (pages == HPAGE_PMD_NR)
>                                 count_vm_event(THP_FILE_FALLBACK);
> --

Thanks
Barry