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

[Gioh Kim]

It's my fault.
I'm going to send another patch ASAP.



2014-07-08 ìì 7:52, Andrew Morton ì ê:
> On Fri, 04 Jul 2014 17:25:09 +0900 Gioh Kim <gioh.kim@xxxxxxx> wrote:
>
> > From: Gioh Kim <gioh.kim@xxxxxxx>
> > Date: Fri, 4 Jul 2014 16:53:22 +0900
> > Subject: [PATCH] [RFC] CMA: clear buffer-head lru before page migration
> >
> > When CMA try to migrate page, some buffer-heads can exist on lru.
> > The bh on lru has non-zero count value so that it cannot be dropped
> > even-if it is not used. We can drop only buffers related to the
> > migrated page, but it can take long time more than dropping all
> > because of searching list. There all buffers in lru are dropped.
> >
> > Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
> > Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx>
> > ---
> >   fs/buffer.c |   13 +++++++++++++
> >   1 file changed, 13 insertions(+)
> >
> > diff --git a/fs/buffer.c b/fs/buffer.c
> > index eba6e4f..4f11b7a 100644
> > --- a/fs/buffer.c
> > +++ b/fs/buffer.c
> > @@ -3233,6 +3233,19 @@ int try_to_free_buffers(struct page *page)
> >          if (PageWriteback(page))
> >                  return 0;
> >
> > +#ifdef CONFIG_CMA
> > +       /*
> > +        * When CMA try to migrate page, some buffer-heads can exist on lru.
> > +        * The bh on lru has non-zero count value so that it cannot
> > +        * be dropped even-if it is not used.
> > +        * We can drop only buffers related to the migrated page,
> > +        * but it can take long time more than dropping all
> > +        * because of searching list.
> > +        * There all buffers in lru are dropped first.
> > +        */
> > +       invalidate_bh_lrus();
> > +#endif
>
> No, this will be tremendously expensive.
>
> 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
> +
>   	/*
>   	 * What we do here is we mark all pageblocks in range as
>   	 * MIGRATE_ISOLATE.  Because pageblock and max order pages may
>
>
> - I'd have thought that it would make sense to do this for huge pages
>    as well (MIGRATE_MOVABLE) but nobody really seems to know.
>
> - There's a patch floating around ("Allow increasing the buffer-head
>    per-CPU LRU size") which will double the size of the bh lrus, so this
>    all becomes more important.
>
> - alloc_contig_range() does lru_add_drain_all() and drain_all_pages()
>    *after* performing the allocation.  I can't work out why this is the
>    case and of course it is undocumented.  If this is indeed not a bug
>    then probably the invalidate_bh_lrus() should happen in the same
>    place.
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