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SubjectRe: [PATCH 2/4] vmscan: get_scan_ratio cleanup
> * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2009-12-28 16:48:06]:
>
> > The get_scan_ratio() should have all scan-ratio related calculations.
> > Thus, this patch move some calculation into get_scan_ratio.
> >
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > ---
> > mm/vmscan.c | 23 ++++++++++++++---------
> > 1 files changed, 14 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 2bbee91..640486b 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1501,6 +1501,13 @@ static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
> > unsigned long ap, fp;
> > struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
> >
> > + /* If we have no swap space, do not bother scanning anon pages. */
> > + if (!sc->may_swap || (nr_swap_pages <= 0)) {
> > + percent[0] = 0;
> > + percent[1] = 100;
> > + return;
> > + }
> > +
>
>
> > anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
> > zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
> > file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
> > @@ -1598,22 +1605,20 @@ static void shrink_zone(int priority, struct zone *zone,
> > unsigned long nr_reclaimed = sc->nr_reclaimed;
> > unsigned long nr_to_reclaim = sc->nr_to_reclaim;
> > struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
> > - int noswap = 0;
> >
> > - /* If we have no swap space, do not bother scanning anon pages. */
> > - if (!sc->may_swap || (nr_swap_pages <= 0)) {
> > - noswap = 1;
> > - percent[0] = 0;
> > - percent[1] = 100;
> > - } else
> > - get_scan_ratio(zone, sc, percent);
> > + get_scan_ratio(zone, sc, percent);
>
> Where do we set noswap? Is percent[0] == 0 used to indicate noswap =
> 1?

Yes, I intended so. I guess your question can convert next sentence.

following case makes different result, is it intentional?
- there are free swap
- sc->may_swap == 1
- priority == 0
- percent[0] == 0

My answer is, it isn't happen on practical workload. if priority reach to 0, vmscan always
scan and reclaim some anon (please recall, now vmscan automatically enable lumpy_reclaim
if priority < 10), then recent_rotated_anon isn't 0 always.. practically.

Do you think this is wrong assumption?


> > for_each_evictable_lru(l) {
> > int file = is_file_lru(l);
> > unsigned long scan;
> >
> > + if (percent[file] == 0) {
> > + nr[l] = 0;
> > + continue;
> > + }
> > +
>
> Is this really needed? Won't nr_scan_try_batch handle it correctly?

this two if branch is nicer than "priority || noswap", I think.
it clearly explain what do it.

>
> > scan = zone_nr_lru_pages(zone, sc, l);
> > - if (priority || noswap) {
> > + if (priority) {
> > scan >>= priority;
> > scan = (scan * percent[file]) / 100;
> > }
>
> --
> Balbir





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