linux-kernel - Re: [PATCH 4/4] (CMA_AGGRESSIVE) Update page alloc function

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Date:	Fri, 24 Oct 2014 14:28:50 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Hui Zhu <zhuhui@...omi.com>
Cc:	rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
	m.szyprowski@...sung.com, akpm@...ux-foundation.org,
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	linux-pm@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/4] (CMA_AGGRESSIVE) Update page alloc function

On Thu, Oct 16, 2014 at 11:35:51AM +0800, Hui Zhu wrote:
> If page alloc function __rmqueue try to get pages from MIGRATE_MOVABLE and
> conditions (cma_alloc_counter, cma_aggressive_free_min, cma_alloc_counter)
> allow, MIGRATE_CMA will be allocated as MIGRATE_MOVABLE first.
> 
> Signed-off-by: Hui Zhu <zhuhui@...omi.com>
> ---
>  mm/page_alloc.c | 42 +++++++++++++++++++++++++++++++-----------
>  1 file changed, 31 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 736d8e1..87bc326 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -65,6 +65,10 @@
>  #include <asm/div64.h>
>  #include "internal.h"
>  
> +#ifdef CONFIG_CMA_AGGRESSIVE
> +#include <linux/cma.h>
> +#endif
> +
>  /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
>  static DEFINE_MUTEX(pcp_batch_high_lock);
>  #define MIN_PERCPU_PAGELIST_FRACTION	(8)
> @@ -1189,20 +1193,36 @@ static struct page *__rmqueue(struct zone *zone, unsigned int order,
>  {
>  	struct page *page;
>  
> -retry_reserve:
> +#ifdef CONFIG_CMA_AGGRESSIVE
> +	if (cma_aggressive_switch
> +	    && migratetype == MIGRATE_MOVABLE
> +	    && atomic_read(&cma_alloc_counter) == 0
> +	    && global_page_state(NR_FREE_CMA_PAGES) > cma_aggressive_free_min
> +							+ (1 << order))
> +		migratetype = MIGRATE_CMA;
> +#endif
> +retry:

I don't get it why cma_alloc_counter should be tested.
When cma alloc is progress, pageblock is isolated so that pages on that
pageblock cannot be allocated. Why should we prevent aggressive
allocation in this case?

Thanks.
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