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

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Date:	Tue, 03 Mar 2015 13:58:46 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	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>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [RFC 13/16] mm/cma: populate ZONE_CMA and use this zone when GFP_HIGHUSERMOVABLE

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 ?

-aneesh

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