linux-kernel - [PATCH 2/3] thp: change deferred_split_count() to return number of THP in queue

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Date:	Thu, 21 Jan 2016 15:09:22 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH 2/3] thp: change deferred_split_count() to return number of THP in queue

I've got meaning of shrinker::count_objects() wrong: it should return
number of potentially freeable objects, which is not necessary correlate
with freeable memory.

Returning 256 per THP in queue is not reasonable:
shrinker::scan_objects() never called with nr_to_scan > 128 in my setup.

Let's return 1 per THP and correct scan_object accordingly.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/huge_memory.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 769ea8db5771..36f98459f854 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3465,12 +3465,7 @@ static unsigned long deferred_split_count(struct shrinker *shrink,
 		struct shrink_control *sc)
 {
 	struct pglist_data *pgdata = NODE_DATA(sc->nid);
-	/*
-	 * Split a page from split_queue will free up at least one page,
-	 * at most HPAGE_PMD_NR - 1. We don't track exact number.
-	 * Let's use HPAGE_PMD_NR / 2 as ballpark.
-	 */
-	return ACCESS_ONCE(pgdata->split_queue_len) * HPAGE_PMD_NR / 2;
+	return ACCESS_ONCE(pgdata->split_queue_len);
 }
 
 static unsigned long deferred_split_scan(struct shrinker *shrink,
@@ -3511,7 +3506,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 	list_splice_tail(&list, &pgdata->split_queue);
 	spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
 
-	return split * HPAGE_PMD_NR / 2;
+	return split;
 }
 
 static struct shrinker deferred_split_shrinker = {
-- 
2.7.0.rc3