Re: [PATCH] mm/compaction: fix missed direct_compaction setting for non-direct compaction

[Yafang Shao <laoar.shao@gmail.com>]

On Fri, Mar 29, 2019 at 4:45 PM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 3/29/19 9:36 AM, Yafang Shao wrote:
> > direct_compaction is not initialized for kcompactd or manually triggered
> > compaction (via /proc or /sys).
>
> It doesn't need to, this style of initialization does guarantee that any
> field not explicitly mentioned is initialized to 0/NULL/false... and
> this pattern is used all over the kernel.
>

Hmm.
You mean the gcc will set the local variable to 0 ?
Are there any reference to this behavior ?

Thanks
Yafang

> > That may cause unexpected behavior in __compact_finished(), so we should
> > set direct_compaction to false explicitly for these compactions.
>
> It's not necessary.
>
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > ---
> >  mm/compaction.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 98f99f4..ba2b711 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -2400,13 +2400,12 @@ static void compact_node(int nid)
> >               .total_free_scanned = 0,
> >               .mode = MIGRATE_SYNC,
> >               .ignore_skip_hint = true,
> > +             .direct_compaction = false,
> >               .whole_zone = true,
> >               .gfp_mask = GFP_KERNEL,
> >       };
> >
> > -
> >       for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
> > -
> >               zone = &pgdat->node_zones[zoneid];
> >               if (!populated_zone(zone))
> >                       continue;
> > @@ -2522,8 +2521,10 @@ static void kcompactd_do_work(pg_data_t *pgdat)
> >               .classzone_idx = pgdat->kcompactd_classzone_idx,
> >               .mode = MIGRATE_SYNC_LIGHT,
> >               .ignore_skip_hint = false,
> > +             .direct_compaction = false,
> >               .gfp_mask = GFP_KERNEL,
> >       };
> > +
> >       trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
> >                                                       cc.classzone_idx);
> >       count_compact_event(KCOMPACTD_WAKE);
> >
>