On Mon, May 22, 2023 at 6:48 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote:
>
> Yosry Ahmed <yosryahmed@xxxxxxxxxx> writes:
>
> > On Mon, May 22, 2023 at 12:09 AM Huang Ying <ying.huang@xxxxxxxxx> wrote:
> >>
> >> __swap_count() is called in do_swap_page() only, which encloses the
> >> call site with get/put_swap_device() already.
> >>
> >> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> >> Cc: David Hildenbrand <david@xxxxxxxxxx>
> >> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> >> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> >> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> >> Cc: Michal Hocko <mhocko@xxxxxxxx>
> >> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> >> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> >> Cc: Yang Shi <shy828301@xxxxxxxxx>
> >> Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
> >> ---
> >> mm/swapfile.c | 10 ++--------
> >> 1 file changed, 2 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/mm/swapfile.c b/mm/swapfile.c
> >> index 274bbf797480..8419cba9c192 100644
> >> --- a/mm/swapfile.c
> >> +++ b/mm/swapfile.c
> >> @@ -1432,16 +1432,10 @@ void swapcache_free_entries(swp_entry_t *entries, int n)
> >>
> >
> > nit: I would add a comment here that the caller needs get/put_swap_device().
>
> It's default behavior to call get/put_swap_device() in the caller for
> all almost all swap functions. I would rather comment the swap
> functions needn't to do that, as the comments for
> read_swap_cache_async() in [2/5].
Fair enough. The comment that you added above get_swap_device() states
that all swap-related functions should have some sort of protection
against swapoff, so I guess that's sufficient.
My concern is that sometimes people don't know where to look, and
having a comment above the function might be helpful. I do agree
though that having a comment above ~all swap-related functions
pointing to the comment above get_swap_device() is too much.
>
> > Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
>
> Thanks!
>
> >> int __swap_count(swp_entry_t entry)
> >> {
> >> - struct swap_info_struct *si;
> >> + struct swap_info_struct *si = swp_swap_info(entry);
> >> pgoff_t offset = swp_offset(entry);
> >> - int count = 0;
> >>
> >> - si = get_swap_device(entry);
> >> - if (si) {
> >> - count = swap_count(si->swap_map[offset]);
> >> - put_swap_device(si);
> >> - }
> >> - return count;
> >> + return swap_count(si->swap_map[offset]);
> >> }
> >>
> >> /*
>
> Best Regards,
> Huang, Ying
