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Date:   Fri, 23 Mar 2018 09:38:47 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Zhaoyang Huang <huangzhaoyang@gmail.com>
Cc:     zhaoyang.huang@spreadtrum.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Mel Gorman <mgorman@techsingularity.net>,
        Johannes Weiner <hannes@cmpxchg.org>,
        vel Tatashin <pasha.tatashin@oracle.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        kernel-patch-test@lists.linaro.org
Subject: Re: [PATCH v1] mm: help the ALLOC_HARDER allocation pass the
 watermarki when CMA on
Message-ID: <20180323083847.GJ23100@dhcp22.suse.cz>
References: <1521791852-7048-1-git-send-email-zhaoyang.huang@spreadtrum.com>
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On Fri 23-03-18 15:57:32, Zhaoyang Huang wrote:
> For the type of 'ALLOC_HARDER' page allocation, there is an express
> highway for the whole process which lead the allocation reach __rmqueue_xxx
> easier than other type.
> However, when CMA is enabled, the free_page within zone_watermark_ok() will
> be deducted for number the pages in CMA type, which may cause the watermark
> check fail, but there are possible enough HighAtomic or Unmovable and
> Reclaimable pages in the zone. So add 'alloc_harder' here to
> count CMA pages in to clean the obstacles on the way to the final.

This is no longer the case in the current mmotm tree. Have a look at
Joonsoo's zone movable based CMA patchset http://lkml.kernel.org/r/1512114786-5085-1-git-send-email-iamjoonsoo.kim@lge.com

> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@spreadtrum.com>
> ---
>  mm/page_alloc.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 635d7dd..cc18620 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3045,8 +3045,11 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
>  
>  
>  #ifdef CONFIG_CMA
> -	/* If allocation can't use CMA areas don't use free CMA pages */
> -	if (!(alloc_flags & ALLOC_CMA))
> +	/*
> +	 * If allocation can't use CMA areas and no alloc_harder set for none
> +	 * order0 allocation, don't use free CMA pages.
> +	 */
> +	if (!(alloc_flags & ALLOC_CMA) && (!alloc_harder || !order))
>  		free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
>  #endif
>  
> -- 
> 1.9.1
> 

-- 
Michal Hocko
SUSE Labs