Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.37 as permitted sender) client-ip=23.128.96.37;
MIME-Version: 1.0
References: <20231119194740.94101-1-ryncsn@gmail.com> <20231119194740.94101-10-ryncsn@gmail.com>
 <87il5wc1nr.fsf@yhuang6-desk2.ccr.corp.intel.com>
In-Reply-To: <87il5wc1nr.fsf@yhuang6-desk2.ccr.corp.intel.com>
From:   Chris Li <chrisl@kernel.org>
Date:   Tue, 21 Nov 2023 00:02:14 -0800
Message-ID: <CAF8kJuOwPMJSsR2+q53gQTjWT9b0XS+AMZGJMOq1veut1OogWA@mail.gmail.com>
Subject: Re: [PATCH 09/24] mm/swap: inline __swap_count
To:     "Huang, Ying" <ying.huang@intel.com>
Cc:     Kairui Song <ryncsn@gmail.com>, linux-mm@kvack.org,
        Kairui Song <kasong@tencent.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        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
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Sun, Nov 19, 2023 at 11:43=E2=80=AFPM Huang, Ying <ying.huang@intel.com>=
 wrote:
>
> Kairui Song <ryncsn@gmail.com> writes:
>
> > From: Kairui Song <kasong@tencent.com>
> >
> > There is only one caller in swap subsystem now, where it can be inline
> > smoothly, avoid the memory access and function call overheads.
> >
> > Signed-off-by: Kairui Song <kasong@tencent.com>
> > ---
> >  include/linux/swap.h | 6 ------
> >  mm/swap_state.c      | 6 +++---
> >  mm/swapfile.c        | 8 --------
> >  3 files changed, 3 insertions(+), 17 deletions(-)
> >
> > diff --git a/include/linux/swap.h b/include/linux/swap.h
> > index 2401990d954d..64a37819a9b3 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -485,7 +485,6 @@ int swap_type_of(dev_t device, sector_t offset);
> >  int find_first_swap(dev_t *device);
> >  extern unsigned int count_swap_pages(int, int);
> >  extern sector_t swapdev_block(int, pgoff_t);
> > -extern int __swap_count(swp_entry_t entry);
> >  extern int swap_swapcount(struct swap_info_struct *si, swp_entry_t ent=
ry);
> >  extern int swp_swapcount(swp_entry_t entry);
> >  extern struct swap_info_struct *page_swap_info(struct page *);
> > @@ -559,11 +558,6 @@ static inline void put_swap_folio(struct folio *fo=
lio, swp_entry_t swp)
> >  {
> >  }
> >
> > -static inline int __swap_count(swp_entry_t entry)
> > -{
> > -     return 0;
> > -}
> > -
> >  static inline int swap_swapcount(struct swap_info_struct *si, swp_entr=
y_t entry)
> >  {
> >       return 0;
> > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > index fb78f7f18ed7..d87c20f9f7ec 100644
> > --- a/mm/swap_state.c
> > +++ b/mm/swap_state.c
> > @@ -316,9 +316,9 @@ void free_pages_and_swap_cache(struct encoded_page =
**pages, int nr)
> >       release_pages(pages, nr);
> >  }
> >
> > -static inline bool swap_use_no_readahead(struct swap_info_struct *si, =
swp_entry_t entry)
> > +static inline bool swap_use_no_readahead(struct swap_info_struct *si, =
pgoff_t offset)
> >  {
> > -     return data_race(si->flags & SWP_SYNCHRONOUS_IO) && __swap_count(=
entry) =3D=3D 1;
> > +     return data_race(si->flags & SWP_SYNCHRONOUS_IO) && swap_count(si=
->swap_map[offset]) =3D=3D 1;
> >  }
> >
> >  static inline bool swap_use_vma_readahead(struct swap_info_struct *si)
> > @@ -928,7 +928,7 @@ struct page *swapin_readahead(swp_entry_t entry, gf=
p_t gfp_mask,
> >
> >       si =3D swp_swap_info(entry);
> >       mpol =3D get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
> > -     if (swap_use_no_readahead(si, entry)) {
> > +     if (swap_use_no_readahead(si, swp_offset(entry))) {
> >               page =3D swapin_no_readahead(entry, gfp_mask, mpol, ilx, =
vmf->vma->vm_mm);
> >               cached =3D false;
> >       } else if (swap_use_vma_readahead(si)) {
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index a8ae472ed2b6..e15a6c464a38 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -1431,14 +1431,6 @@ void swapcache_free_entries(swp_entry_t *entries=
, int n)
> >               spin_unlock(&p->lock);
> >  }
> >
> > -int __swap_count(swp_entry_t entry)
> > -{
> > -     struct swap_info_struct *si =3D swp_swap_info(entry);
> > -     pgoff_t offset =3D swp_offset(entry);
> > -
> > -     return swap_count(si->swap_map[offset]);
> > -}
> > -
>
> I'd rather keep __swap_count() in the original place together with other
> swap count related functions.  And si->swap_map[] was hided in
> swapfile.c before.  I don't think the change will have any real
> performance improvement.

I agree with Ying here. Does not seem to have value high enough to
justify a patch by itself.

Chris