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

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Date:	Thu,  8 May 2014 09:32:22 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	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>,
	Michal Nazarewicz <mina86@...a86.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH 1/3] CMA: remove redundant retrying code in __alloc_contig_migrate_range

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>

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);
-- 
1.7.9.5

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