Re: [PATCH] mm/compaction: Remove some useless code in compact_zone()

[Xu, Yanfei]

On 10/16/20 11:05 PM, Vlastimil Babka wrote:
> On 10/14/20 2:28 PM, David Hildenbrand wrote:
> > On 14.10.20 09:23, yanfei.xu@xxxxxxxxxxxxx wrote:
> > > From: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
> > >
> > > start_pfn has been declared at the begin of compact_zone(), it's
> > > no need to declare it again. And remove an useless semicolon.
> > >
> > > Signed-off-by: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
> > > ---
> > >  mm/compaction.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/mm/compaction.c b/mm/compaction.c
> > > index 176dcded298e..5e69c1f94d96 100644
> > > --- a/mm/compaction.c
> > > +++ b/mm/compaction.c
> > > @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, struct 
> > > capture_control *capc)
> > >
> > >      while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
> > >          int err;
> > > -        unsigned long start_pfn = cc->migrate_pfn;
> > > +        start_pfn = cc->migrate_pfn;
> >
> > There is a user in
> >
> > trace_mm_compaction_end(start_pfn, cc->migrate_pfn, cc->free_pfn,
> > end_pfn, sync, ret);
> >
> > we would now trace a different value, no?
>
> Agreed. We should rather rename the while-local one to avoid confusion. 
> Something like "iteration_start_pfn" ?

Thank you, David and Vlastimil, for pointing out the impact to the 
tracepoint. I think "iteration_start_pfn" is appropriate and will send V2.

> > >          /*
> > >           * Avoid multiple rescans which can happen if a page cannot be
> > > @@ -2309,7 +2309,6 @@ compact_zone(struct compact_control *cc, struct 
> > > capture_control *capc)
> > >          case ISOLATE_SUCCESS:
> > >              update_cached = false;
> > >              last_migrated_pfn = start_pfn;
> > > -            ;
> >
> > Huh, how does something like that happen :)
>
> Looks like "case ISOLATE_SUCCESS:" used to be an empty implementation, 
> then statements got added, but semicolon not removed.

Yup, this case used to be an empty.