Re: [PATCH] mm: cma: free cma page to buddy instead of being cpu hot page

[Zhang Mingjun <zhang.mingjun@linaro.org>]

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On Tue, Oct 29, 2013 at 5:33 PM, Mel Gorman <mgorman@suse.de> wrote:

> On Mon, Oct 28, 2013 at 07:42:49PM +0800, zhang.mingjun@linaro.org wrote:
> > From: Mingjun Zhang <troy.zhangmingjun@linaro.org>
> >
> > free_contig_range frees cma pages one by one and MIGRATE_CMA pages will
> be
> > used as MIGRATE_MOVEABLE pages in the pcp list, it causes unnecessary
> > migration action when these pages reused by CMA.
> >
> > Signed-off-by: Mingjun Zhang <troy.zhangmingjun@linaro.org>
> > ---
> >  mm/page_alloc.c |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 0ee638f..84b9d84 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1362,7 +1362,8 @@ void free_hot_cold_page(struct page *page, int
> cold)
> >        * excessively into the page allocator
> >        */
> >       if (migratetype >= MIGRATE_PCPTYPES) {
> > -             if (unlikely(is_migrate_isolate(migratetype))) {
> > +             if (unlikely(is_migrate_isolate(migratetype))
> > +                     || is_migrate_cma(migratetype))
> >                       free_one_page(zone, page, 0, migratetype);
> >                       goto out;
>
> This slightly impacts the page allocator free path for a marginal gain
> on CMA which are relatively rare allocations. There is no obvious
> benefit to this patch as I expect CMA allocations to flush the PCP lists
>
how about keeping the migrate type of CMA page block as MIGRATE_ISOLATED
after
the alloc_contig_range , and undo_isolate_page_range at the end of
free_contig_range?
of course, it will waste the memory outside of the alloc range but in the
pageblocks.

> when a range of pages have been isolated and migrated. Is there any
> measurable benefit to this patch?
>
> after applying this patch, the video player on my platform works more
fluent,
and the driver of video decoder on my test platform using cma alloc/free
frequently.

> -- Mel Gorman
> SUSE Labs
>

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