linux-kernel - Re: [RFC][PATCH 1/2] mm: use MIGRATE

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Date:   Tue, 7 Mar 2017 11:47:58 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Xishi Qiu <qiuxishi@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Minchan Kim <minchan@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/2] mm: use MIGRATE_HIGHATOMIC as late as possible

On Tue 07-03-17 18:33:53, Xishi Qiu wrote:
> MIGRATE_HIGHATOMIC page blocks are reserved for an atomic
> high-order allocation, so use it as late as possible.

Why is this better? Are you seeing any problem which this patch
resolves? In other words the patch description should explain why not
only what (that is usually clear from looking at the diff).

> Signed-off-by: Xishi Qiu <qiuxishi@...wei.com>
> ---
>  mm/page_alloc.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 40d79a6..2331840 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2714,14 +2714,12 @@ struct page *rmqueue(struct zone *preferred_zone,
>  	spin_lock_irqsave(&zone->lock, flags);
>  
>  	do {
> -		page = NULL;
> -		if (alloc_flags & ALLOC_HARDER) {
> +		page = __rmqueue(zone, order, migratetype);
> +		if (!page && alloc_flags & ALLOC_HARDER) {
>  			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
>  			if (page)
>  				trace_mm_page_alloc_zone_locked(page, order, migratetype);
>  		}
> -		if (!page)
> -			page = __rmqueue(zone, order, migratetype);
>  	} while (page && check_new_pages(page, order));
>  	spin_unlock(&zone->lock);
>  	if (!page)
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs