linux-kernel - Re: [PATCH 14/24] mm/swap: do shadow lookup as well when doing swap cache lookup

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Date:   Tue, 21 Nov 2023 08:55:13 -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 14/24] mm/swap: do shadow lookup as well when doing swap
 cache lookup

Hi Kairui,

Too trivial to stand alone as a patch. Merge it with the patch needed
to use that "*shadow".

Chris

On Sun, Nov 19, 2023 at 11:48 AM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> Make swap_cache_get_folio capable of returning the shadow value when the
> xarray contains a shadow instead of a valid folio. Just extend the
> arguments to be used later.
>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---
>  mm/shmem.c      |  2 +-
>  mm/swap.h       |  2 +-
>  mm/swap_state.c | 11 +++++++----
>  3 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 72239061c655..f9ce4067c742 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1875,7 +1875,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
>         }
>
>         /* Look it up and read it in.. */
> -       folio = swap_cache_get_folio(swap, NULL);
> +       folio = swap_cache_get_folio(swap, NULL, NULL);
>         if (!folio) {
>                 /* Or update major stats only when swapin succeeds?? */
>                 if (fault_type) {
> diff --git a/mm/swap.h b/mm/swap.h
> index e43e965f123f..da9deb5ba37d 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -47,7 +47,7 @@ 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);
> +                                  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 3b5a34f47192..e057c79fb06f 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -334,14 +334,17 @@ 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)
> +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_folio(swap_address_space(entry), swp_offset(entry));
> -       if (IS_ERR(folio))
> +       folio = filemap_get_entry(swap_address_space(entry), swp_offset(entry));
> +       if (xa_is_value(folio)) {
> +               if (shadowp)
> +                       *shadowp = folio;
>                 return NULL;
> +       }
>
>         /*
>          * At the moment, we don't support PG_readahead for anon THP
> @@ -923,7 +926,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
>         struct page *page;
>         pgoff_t ilx;
>
> -       folio = swap_cache_get_folio(entry, vmf);
> +       folio = swap_cache_get_folio(entry, vmf, NULL);
>         if (folio) {
>                 page = folio_file_page(folio, swp_offset(entry));
>                 cache_result = SWAP_CACHE_HIT;
> --
> 2.42.0
>
>