linux-kernel - Re: [PATCH v3 3/7] mm/compaction: initialize compact_order_failed to MAX

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Date:	Fri, 4 Dec 2015 16:36:28 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Joonsoo Kim <js1304@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v3 3/7] mm/compaction: initialize compact_order_failed to
 MAX_ORDER

On 12/03/2015 08:11 AM, Joonsoo Kim wrote:
> If compact_order_failed is initialized to 0 and order-9
> compaction is continually failed, defer counter will be updated
> to activate deferring. Although other defer counters will be properly
> updated, compact_order_failed will not be updated because failed order
> cannot be lower than compact_order_failed, 0. In this case,
> low order compaction such as 2, 3 could be deferred due to
> this wrongly initialized compact_order_failed value. This patch
> removes this possibility by initializing it to MAX_ORDER.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

Good catch.

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>   mm/page_alloc.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d0499ff..7002c66 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5273,6 +5273,9 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
>   		zone_seqlock_init(zone);
>   		zone->zone_pgdat = pgdat;
>   		zone_pcp_init(zone);
> +#ifdef CONFIG_COMPACTION
> +		zone->compact_order_failed = MAX_ORDER;
> +#endif
>
>   		/* For bootup, initialized properly in watermark setup */
>   		mod_zone_page_state(zone, NR_ALLOC_BATCH, zone->managed_pages);
>

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