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From:   Chris Li <chrisl@kernel.org>
Date:   Tue, 21 Nov 2023 09:15:50 -0800
Message-ID: <CAF8kJuM3Czmr1Up9mYGK9k9HH8r0CHkXvZ8rWyqniM4vtExF+Q@mail.gmail.com>
Subject: Re: [PATCH 15/24] mm/swap: avoid an duplicated swap cache lookup for
 SYNCHRONOUS_IO device
To:     Kairui Song <kasong@tencent.com>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        "Huang, Ying" <ying.huang@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@suse.com>, linux-kernel@vger.kernel.org
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On Sun, Nov 19, 2023 at 11:48=E2=80=AFAM Kairui Song <ryncsn@gmail.com> wro=
te:
>
> From: Kairui Song <kasong@tencent.com>
>
> When a xa_value is returned by the cache lookup, keep it to be used
> later for workingset refault check instead of doing the looking up again
> in swapin_no_readahead.
>
> This does have a side effect of making swapoff also triggers workingset
> check, but should be fine since swapoff does effect the workload in many
> ways already.

I need to sleep on it a bit to see if this will create another problem or n=
ot.

>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---
>  mm/swap_state.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index e057c79fb06f..51de2a0412df 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -872,7 +872,6 @@ static struct page *swapin_no_readahead(swp_entry_t e=
ntry, gfp_t gfp_mask,
>  {
>         struct folio *folio;
>         struct page *page;
> -       void *shadow =3D NULL;
>
>         page =3D alloc_pages_mpol(gfp_mask, 0, mpol, ilx, numa_node_id())=
;
>         folio =3D (struct folio *)page;
> @@ -888,10 +887,6 @@ static struct page *swapin_no_readahead(swp_entry_t =
entry, gfp_t gfp_mask,
>
>                 mem_cgroup_swapin_uncharge_swap(entry);
>
> -               shadow =3D get_shadow_from_swap_cache(entry);
> -               if (shadow)
> -                       workingset_refault(folio, shadow);
> -
>                 folio_add_lru(folio);
>
>                 /* To provide entry to swap_readpage() */
> @@ -922,11 +917,12 @@ struct page *swapin_readahead(swp_entry_t entry, gf=
p_t gfp_mask,
>         enum swap_cache_result cache_result;
>         struct swap_info_struct *si;
>         struct mempolicy *mpol;
> +       void *shadow =3D NULL;
>         struct folio *folio;
>         struct page *page;
>         pgoff_t ilx;
>
> -       folio =3D swap_cache_get_folio(entry, vmf, NULL);
> +       folio =3D swap_cache_get_folio(entry, vmf, &shadow);
>         if (folio) {
>                 page =3D folio_file_page(folio, swp_offset(entry));
>                 cache_result =3D SWAP_CACHE_HIT;
> @@ -938,6 +934,8 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_=
t gfp_mask,
>         if (swap_use_no_readahead(si, swp_offset(entry))) {
>                 page =3D swapin_no_readahead(entry, gfp_mask, mpol, ilx, =
vmf->vma->vm_mm);
>                 cache_result =3D SWAP_CACHE_BYPASS;
> +               if (shadow)
> +                       workingset_refault(page_folio(page), shadow);

It is inconsistent why other flavors of readahead do not do the
workingset_refault here.
I suggest keeping the workingset_refault in swapin_no_readahead() and
pass the shadow argument in.

Chris

>         } else if (swap_use_vma_readahead(si)) {
>                 page =3D swap_vma_readahead(entry, gfp_mask, mpol, ilx, v=
mf);
>                 cache_result =3D SWAP_CACHE_MISS;
> --
> 2.42.0
>
>