Re: [PATCH v6 05/11] mm, compaction: add the ultimate direct compaction priority

[Vlastimil Babka]

On 08/16/2016 07:58 AM, Joonsoo Kim wrote:
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -1644,6 +1644,8 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
> >  		.alloc_flags = alloc_flags,
> >  		.classzone_idx = classzone_idx,
> >  		.direct_compaction = true,
> > +		.whole_zone = (prio == COMPACT_PRIO_SYNC_FULL),
> > +		.ignore_skip_hint = (prio == COMPACT_PRIO_SYNC_FULL)
> >  	};
> >  	INIT_LIST_HEAD(&cc.freepages);
> >  	INIT_LIST_HEAD(&cc.migratepages);
> > @@ -1689,7 +1691,8 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
> >  								ac->nodemask) {
> >  		enum compact_result status;
> >
> > -		if (compaction_deferred(zone, order)) {
> > +		if (prio > COMPACT_PRIO_SYNC_FULL
> > +					&& compaction_deferred(zone, order)) {
> >  			rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
> >  			continue;
>
> Could we provide prio to compaction_deferred() and do the decision in
> that that function?
>
> BTW, in kcompactd, compaction_deferred() is checked but
> .ignore_skip_hint=true. Is there any reason? If we can remove
> compaction_deferred() for kcompactd, we can check .ignore_skip_hint
> to determine if defer is needed or not.

I don't want to change kcompactd right now, as the current series seems 
to help against premature OOMs. But I'll revisit it later.

Thanks.