Re: [PATCH] [RFC] mm/compaction: initialize compaction information

[Vlastimil Babka]

On 03/20/2015 12:33 AM, Gioh Kim wrote:
> > > diff --git a/mm/compaction.c b/mm/compaction.c
> > > index 8c0d945..827ec06 100644
> > > --- a/mm/compaction.c
> > > +++ b/mm/compaction.c
> > > @@ -1587,8 +1587,10 @@ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
> > >                    INIT_LIST_HEAD(&cc->freepages);
> > >                    INIT_LIST_HEAD(&cc->migratepages);
> > >
> > > -               if (cc->order == -1 || !compaction_deferred(zone, cc->order))
> > > +               if (cc->order == -1 || !compaction_deferred(zone, cc->order)) {
> > > +                       __reset_isolation_suitable(zone);
> >
> > This will also trigger reset when called from kswapd through compact_pgdat() and
> > !compaction_deferred() is true.
> > The reset should be restricted to cc->order == -1 which only happens from /proc
> > trigger.
> >
> > >                            compact_zone(zone, cc);
> > > +               }
> > >
> > >                    if (cc->order > 0) {
> > >                            if (zone_watermark_ok(zone, cc->order,
>
> I've not been familiar with compaction code.
> I think cc->order is -1 only if __compact_pgdat is called via /proc.

Yes that's what I meant.

> This is ugly but I don't have better solution.
> Do you have better idea?

It's not ugly IMHO. There are more tests for -1 like this, e.g. in
compaction_suitable(). Maybe just add some comment such as:

/*
 * When called via /proc/sys/vm/compact_memory make sure we compact
 * the whole zone regardless of cached scanner positions.
 */

> diff --git a/mm/compaction.c b/mm/compaction.c
> index 8c0d945..5b4e255 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1587,6 +1587,9 @@ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
>                   INIT_LIST_HEAD(&cc->freepages);
>                   INIT_LIST_HEAD(&cc->migratepages);
>
> +               if (cc->order == -1)
> +                       __reset_isolation_suitable(zone);
> +
>                   if (cc->order == -1 || !compaction_deferred(zone, cc->order))
>                           compact_zone(zone, cc);

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