linux-kernel - [PATCH 3/5] mm: vmscan: remove old flusher wakeup from direct reclaim path

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Date:   Mon, 23 Jan 2017 13:16:39 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH 3/5] mm: vmscan: remove old flusher wakeup from direct reclaim path

Direct reclaim has been replaced by kswapd reclaim in pretty much all
common memory pressure situations, so this code most likely doesn't
accomplish the described effect anymore. The previous patch wakes up
flushers for all reclaimers when we encounter dirty pages at the tail
end of the LRU. Remove the crufty old direct reclaim invocation.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/vmscan.c | 17 -----------------
 1 file changed, 17 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 56ea8d24041f..915fc658de41 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2757,8 +2757,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 					  struct scan_control *sc)
 {
 	int initial_priority = sc->priority;
-	unsigned long total_scanned = 0;
-	unsigned long writeback_threshold;
 retry:
 	delayacct_freepages_start();
 
@@ -2771,7 +2769,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 		sc->nr_scanned = 0;
 		shrink_zones(zonelist, sc);
 
-		total_scanned += sc->nr_scanned;
 		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
 			break;
 
@@ -2784,20 +2781,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 		 */
 		if (sc->priority < DEF_PRIORITY - 2)
 			sc->may_writepage = 1;
-
-		/*
-		 * Try to write back as many pages as we just scanned.  This
-		 * tends to cause slow streaming writers to write data to the
-		 * disk smoothly, at the dirtying rate, which is nice.   But
-		 * that's undesirable in laptop mode, where we *want* lumpy
-		 * writeout.  So in laptop mode, write out the whole world.
-		 */
-		writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
-		if (total_scanned > writeback_threshold) {
-			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
-						WB_REASON_VMSCAN);
-			sc->may_writepage = 1;
-		}
 	} while (--sc->priority >= 0);
 
 	delayacct_freepages_end();
-- 
2.11.0