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    SubjectRe: [patch 2/2] mm: vmscan: drop nr_force_scan[] from get_scan_count
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    On Fri, Aug 12, 2011 at 5:31 AM, Johannes Weiner <jweiner@redhat.com> wrote:
    > The nr_force_scan[] tuple holds the effective scan numbers for anon
    > and file pages in case the situation called for a forced scan and the
    > regularly calculated scan numbers turned out zero.
    >
    > However, the effective scan number can always be assumed to be
    > SWAP_CLUSTER_MAX right before the division into anon and file.  The
    > numerators and denominator are properly set up for all cases, be it
    > force scan for just file, just anon, or both, to do the right thing.
    >
    > Signed-off-by: Johannes Weiner <jweiner@redhat.com>

    Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

    There is a nitpick at below.

    > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > Cc: Michal Hocko <mhocko@suse.cz>
    > Cc: Ying Han <yinghan@google.com>
    > Cc: Balbir Singh <bsingharora@gmail.com>
    > Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    > Cc: Mel Gorman <mel@csn.ul.ie>
    > ---
    >  mm/vmscan.c |   24 ++----------------------
    >  1 files changed, 2 insertions(+), 22 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 96061d7..45f0986 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -1831,7 +1831,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
    >        enum lru_list l;
    >        int noswap = 0;
    >        bool force_scan = false;
    > -       unsigned long nr_force_scan[2];
    >
    >        /* kswapd does zone balancing and need to scan this zone */
    >        if (scanning_global_lru(sc) && current_is_kswapd())
    > @@ -1846,8 +1845,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
    >                fraction[0] = 0;
    >                fraction[1] = 1;
    >                denominator = 1;
    > -               nr_force_scan[0] = 0;
    > -               nr_force_scan[1] = SWAP_CLUSTER_MAX;
    >                goto out;
    >        }
    >
    > @@ -1864,8 +1861,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
    >                        fraction[0] = 1;
    >                        fraction[1] = 0;
    >                        denominator = 1;
    > -                       nr_force_scan[0] = SWAP_CLUSTER_MAX;
    > -                       nr_force_scan[1] = 0;
    >                        goto out;
    >                }
    >        }
    > @@ -1914,11 +1909,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
    >        fraction[0] = ap;
    >        fraction[1] = fp;
    >        denominator = ap + fp + 1;
    > -       if (force_scan) {
    > -               unsigned long scan = SWAP_CLUSTER_MAX;
    > -               nr_force_scan[0] = div64_u64(scan * ap, denominator);
    > -               nr_force_scan[1] = div64_u64(scan * fp, denominator);
    > -       }
    >  out:
    >        for_each_evictable_lru(l) {
    >                int file = is_file_lru(l);
    > @@ -1927,20 +1917,10 @@ out:
    >                scan = zone_nr_lru_pages(zone, sc, l);
    >                if (priority || noswap) {
    >                        scan >>= priority;
    > +                       if (!scan && force_scan)
    > +                               scan = SWAP_CLUSTER_MAX;
    >                        scan = div64_u64(scan * fraction[file], denominator);
    >                }
    > -
    > -               /*
    > -                * If zone is small or memcg is small, nr[l] can be 0.
    > -                * This results no-scan on this priority and priority drop down.
    > -                * For global direct reclaim, it can visit next zone and tend
    > -                * not to have problems. For global kswapd, it's for zone
    > -                * balancing and it need to scan a small amounts. When using
    > -                * memcg, priority drop can cause big latency. So, it's better
    > -                * to scan small amount. See may_noscan above.
    > -                */

    Please move this comment with tidy-up at where making force_scan true.
    Of course, we can find it by git log[246e87a9393] but as I looked the
    git log, it explain this comment indirectly and it's not
    understandable to newbies. I think this comment is more understandable
    than changelog in git.



    --
    Kind regards,
    Minchan Kim
    --
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