linux-kernel - Re: [PATCH 20/24] swap: simplify and make swap_find

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Date:   Tue, 21 Nov 2023 21:01:00 -0800
From:   Chris Li <chrisl@...nel.org>
To:     Kairui Song <kasong@...cent.com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        "Huang, Ying" <ying.huang@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 20/24] swap: simplify and make swap_find_cache static

On Sun, Nov 19, 2023 at 11:49 AM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> There are only two callers within the same file now, make it static and
> drop the redundant if check on the shadow variable.
>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---
>  mm/swap.h       | 2 --
>  mm/swap_state.c | 5 ++---
>  2 files changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/mm/swap.h b/mm/swap.h
> index b073c29c9790..4402970547e7 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -46,8 +46,6 @@ void __delete_from_swap_cache(struct folio *folio,
>  void delete_from_swap_cache(struct folio *folio);
>  void clear_shadow_from_swap_cache(int type, unsigned long begin,
>                                   unsigned long end);
> -struct folio *swap_cache_get_folio(swp_entry_t entry,
> -                                  struct vm_fault *vmf, void **shadowp);
>  struct folio *filemap_get_incore_folio(struct address_space *mapping,
>                 pgoff_t index);
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index eef66757c615..6f39aa8394f1 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -334,15 +334,14 @@ static inline bool swap_use_vma_readahead(struct swap_info_struct *si)
>   *
>   * Caller must lock the swap device or hold a reference to keep it valid.
>   */
> -struct folio *swap_cache_get_folio(swp_entry_t entry, struct vm_fault *vmf, void **shadowp)
> +static struct folio *swap_cache_get_folio(swp_entry_t entry, struct vm_fault *vmf, void **shadowp)
>  {
>         bool vma_ra, readahead;
>         struct folio *folio;
>
>         folio = filemap_get_entry(swap_address_space(entry), swp_offset(entry));
>         if (xa_is_value(folio)) {
> -               if (shadowp)
> -                       *shadowp = folio;
> +               *shadowp = folio;

I prefer to keep the original code to perform the check before
assigning it. The caller usage situation might change.
It is more defensive.

Does not seem to justify it as a standalone patch.

Chris