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

[Gioh Kim]

2015-03-19 ìí 6:01ì Vlastimil Babka ì(ê) ì ê:
> On 03/19/2015 09:52 AM, Gioh Kim wrote:
> > 2015-03-19 ìí 5:41ì Vlastimil Babka ì(ê) ì ê:
> > > On 03/19/2015 06:30 AM, Gioh Kim wrote:
> > >
> > > The code below this comment already does the initialization if the cached values
> > > are outside zone boundaries (e.g. due to not being initialized). So if I go
> > > through what your __reset_isolation_suitable(zone) call possibly fixes:
> > >
> > > - the code below comment should take care of zone->compact_cached_migrate_pfn
> > > and zone->compact_cached_free_pfn.
> > > - the value of zone->compact_blockskip_flush shouldn't affect whether compaction
> > > is done.
> > > - the state of pageblock_skip bits shouldn't matter for compaction via
> > > /proc/sys... as that sets ignore_skip_hint = true
> > >
> > > It might be perhaps possible that the cached scanner positions are close to
> > > meeting and compaction occurs but doesn't process much. That would be also true
> > > if both were zero, but at least on my x86 system, lowest zone's start_pfn is 1
> > > so that would be detected and corrected. Maybe it is zero on yours though? (ARM?).
> >
> > YES, it is. As comment above, my platform is based on ARM.
>
> Ah, I see.
>
> > zone's start_pfn is 0.
>
> OK, good to know that's possible. In that case it's clear that the proper
> initialization doesn't happen, and __compact_finished() decides that scanners
> have already met at pfn 0.
>
> > > So in any case, the problem should be identified in more detail so we know the
> > > fix is not accidental. It could be also worthwile to always reset scanner
> > > positions when doing a /proc triggered compaction, so it's not depending on what
> > > happened before.
> >
> > Excuse my poor english.
> > I cannot catch exactly what you want.
> > Is this what you want? This resets the position if compaction is started via /proc.
>
> Yes that's right, but..
>
> > 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.
This is ugly but I don't have better solution.
Do you have better idea?


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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