linux-kernel - Re: [RFC PATCH 1/3] CMA: remove redundant retrying code in __alloc_contig_migrate

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Date:	Fri, 09 May 2014 08:44:06 -0700
From:	Michal Nazarewicz <mina86@...a86.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>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Minchan Kim <minchan@...nel.org>,
	Heesub Shin <heesub.shin@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] CMA: remove redundant retrying code in __alloc_contig_migrate_range

On Wed, May 07 2014, Joonsoo Kim wrote:
> We already have retry logic in migrate_pages(). It does retry 10 times.
> So if we keep this retrying code in __alloc_contig_migrate_range(), we
> would try to migrate some unmigratable page in 50 times. There is just one
> small difference in -ENOMEM case. migrate_pages() don't do retry
> in this case, however, current __alloc_contig_migrate_range() does. But,
> I think that this isn't problem, because in this case, we may fail again
> with same reason.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

I think there was a reason for the retries in
__alloc_contig_migrate_range but perhaps those are no longer valid.

Acked-by: Michal Nazarewicz <mina86@...a86.com>

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5dba293..674ade7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6185,7 +6185,6 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
>  	/* This function is based on compact_zone() from compaction.c. */
>  	unsigned long nr_reclaimed;
>  	unsigned long pfn = start;
> -	unsigned int tries = 0;
>  	int ret = 0;
>  
>  	migrate_prep();
> @@ -6204,10 +6203,6 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
>  				ret = -EINTR;
>  				break;
>  			}
> -			tries = 0;
> -		} else if (++tries == 5) {
> -			ret = ret < 0 ? ret : -EBUSY;
> -			break;
>  		}
>  
>  		nr_reclaimed = reclaim_clean_pages_from_list(cc->zone,
> @@ -6216,6 +6211,10 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
>  
>  		ret = migrate_pages(&cc->migratepages, alloc_migrate_target,
>  				    0, MIGRATE_SYNC, MR_CMA);
> +		if (ret) {
> +			ret = ret < 0 ? ret : -EBUSY;
> +			break;
> +		}
>  	}
>  	if (ret < 0) {
>  		putback_movable_pages(&cc->migratepages);

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +--<mpn@...gle.com>--<xmpp:mina86@...ber.org>--ooO--(_)--Ooo--


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