Re: [PATCH] [RFC] CMA: clear buffer-head lru before page migration

[Gioh Kim]

2014-07-15 ìì 5:37, Andrew Morton ì ê:
> On Mon, 14 Jul 2014 16:02:25 +0900 Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
>
> > On Tue, Jul 08, 2014 at 06:46:31PM +0200, Michal Nazarewicz wrote:
> > > On Mon, Jul 07 2014, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > > What I proposed is that CMA call invalidate_bh_lrus() right at the
> > > > outset.  Something along the lines of
> > > >
> > > > --- a/mm/page_alloc.c~a
> > > > +++ a/mm/page_alloc.c
> > > > @@ -6329,6 +6329,14 @@ int alloc_contig_range(unsigned long sta
> > > >   	};
> > > >   	INIT_LIST_HEAD(&cc.migratepages);
> > > >
> > > > +#ifdef CONFIG_CMA
> > > > +	/*
> > > > +	 * Comment goes here
> > > > +	 */
> > > > +	if (migratetype == MIGRATE_CMA)
> > > > +		invalidate_bh_lrus();
> > > > +#endif
> > > > +
> > >
> > > This seems reasonable, except I think it should go after
> > > start_isolate_page_range call because otherwise there's no guarantee
> > > that someone won't grab those pages back.
> > >
> > > Also to avoid the #ifdef perhaps we want this as well:
> >
> > I think that we just want to remove ifdef CONFIG_CMA on above code
> > snippet, because invalidate_bh_lrus() would also help user of
> > alloc_contig_range() with MIGRATE_MOVABLE.
>
> That's what I believe also.  I pinged Mel and Johannes off-list and Mel
> said "I hit it, the invalidation cost wasn't worth it for a THP alloc".
>
> So hm.  I do think it's worth additional investigation but some careful
> testing would be needed to demonstrate that it's worthwhile.  If the
> invalidation cost is hurting then perhaps additional logic will be
> needed to perform the invalidation only as a last-resort thing.
Adding invalidate_bh_lrus() between start_isolate_page_range and
__alloc_contig_migrate_range is working well on my platform.

But I'd like to test performance before sending patch.
Would anybody recommend me a benchmark tool?



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