Re: [v7 PATCH 04/12] mm: vmscan: remove memcg_shrinker_map_size

From: Yang Shi <shy828301@gmail.com>
To: Roman Gushchin <guro@fb.com>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Shakeel Butt <shakeelb@google.com>,
	Dave Chinner <david@fromorbit.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux MM <linux-mm@kvack.org>,
	Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [v7 PATCH 04/12] mm: vmscan: remove memcg_shrinker_map_size
Date: Tue, 9 Feb 2021 15:31:17 -0800	[thread overview]
Message-ID: <CAHbLzkpcvF578TPB-tfh=MhDqTB5Oc7Sf_6ndV2uZL227o6dFQ@mail.gmail.com> (raw)
In-Reply-To: <20210209204314.GG524633@carbon.DHCP.thefacebook.com>

On Tue, Feb 9, 2021 at 12:43 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Tue, Feb 09, 2021 at 09:46:38AM -0800, Yang Shi wrote:
> > Both memcg_shrinker_map_size and shrinker_nr_max is maintained, but actually the
> > map size can be calculated via shrinker_nr_max, so it seems unnecessary to keep both.
> > Remove memcg_shrinker_map_size since shrinker_nr_max is also used by iterating the
> > bit map.
> >
> > Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > ---
> >  mm/vmscan.c | 18 +++++++++---------
> >  1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index e4ddaaaeffe2..641077b09e5d 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -185,8 +185,10 @@ static LIST_HEAD(shrinker_list);
> >  static DECLARE_RWSEM(shrinker_rwsem);
> >
> >  #ifdef CONFIG_MEMCG
> > +static int shrinker_nr_max;
> >
> > -static int memcg_shrinker_map_size;
> > +#define NR_MAX_TO_SHR_MAP_SIZE(nr_max) \
> > +     (DIV_ROUND_UP(nr_max, BITS_PER_LONG) * sizeof(unsigned long))
>
> How about something like this?
>
> static inline int shrinker_map_size(int nr_items)
> {
>         return DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long);
> }
>
> I think it look less cryptic.

OK, I don't have a strong opinion for either one (inline function or
macro). If no one objects this I could do it in the new version.

>
> The rest of the patch looks good to me.
>
> Thanks!