linux-kernel - Re: [RFC 13/16] mm/cma: populate ZONE_CMA and use this zone when GFP

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Date:	Fri, 6 Mar 2015 16:13:22 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	Laura Abbott <lauraa@...eaurora.org>,
	Minchan Kim <minchan@...nel.org>,
	Heesub Shin <heesub.shin@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Hui Zhu <zhuhui@...omi.com>,
	Gioh Kim <gioh.kim@....com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Ritesh Harjani <ritesh.list@...il.com>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [RFC 13/16] mm/cma: populate ZONE_CMA and use this zone when
 GFP_HIGHUSERMOVABLE

On Tue, Mar 03, 2015 at 01:58:46PM +0530, Aneesh Kumar K.V wrote:
> Joonsoo Kim <iamjoonsoo.kim@....com> writes:
> 
> > Until now, reserved pages for CMA are managed altogether with normal
> > page in the same zone. This approach has numorous problems and fixing
> > them isn't easy. To fix this situation, ZONE_CMA is introduced in
> > previous patch, but, not yet populated. This patch implement population
> > of ZONE_CMA by stealing reserved pages from normal zones. This stealing
> > break one uncertain assumption on zone, that is, zone isn't overlapped.
> > In the early of this series, some check is inserted to every zone's span
> > iterator to handle zone overlap so there would be no problem with
> > this assumption break.
> >
> > To utilize this zone, user should use GFP_HIGHUSERMOVABLE, because
> > these pages are only applicable for movable type and ZONE_CMA could
> > contain highmem.
> >
> > Implementation itself is very easy to understand. Do steal when cma
> > area is initialized and recalculate values for per zone data structure.
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> > ---
> >  include/linux/gfp.h |   10 ++++++++--
> >  include/linux/mm.h  |    1 +
> >  mm/cma.c            |   23 ++++++++++++++++-------
> >  mm/page_alloc.c     |   42 +++++++++++++++++++++++++++++++++++++++---
> >  4 files changed, 64 insertions(+), 12 deletions(-)
> >
> > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > index 619eb20..d125440 100644
> > --- a/include/linux/gfp.h
> > +++ b/include/linux/gfp.h
> > @@ -186,6 +186,12 @@ static inline int gfpflags_to_migratetype(const gfp_t gfp_flags)
> >  #define OPT_ZONE_DMA32 ZONE_NORMAL
> >  #endif
> >  
> > +#ifdef CONFIG_CMA
> > +#define OPT_ZONE_CMA ZONE_CMA
> > +#else
> > +#define OPT_ZONE_CMA ZONE_MOVABLE
> > +#endif
> > +
> 
> Does that mean with CONFIG_CMA we always try ZONE_CMA first and then
> fallback to ZONE_MOVABLE ? If so won't we hit termporary CMA allocation
> failures that can result with pinned movable pages ?

Hello, Aneesh.

IIUC, Johannes's fair allocation policy patchset makes us uses
individual zones fairly. So, before freepage on ZONE_CMA is exhausted,
ZONE_MOVABLE will be used. :)

Thanks.
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