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From:   Wonhyuk Yang <vvghjk1234@gmail.com>
To:     vvghjk1234@gmail.com, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Roman Gushchin <roman.gushchin@linux.dev>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH] mm/slub: Remove repeated action in calculate_order()
Date:   Sat, 16 Apr 2022 15:11:04 +0900
Message-Id: <20220416061104.481674-1-vvghjk1234@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

To calculate order, calc_slab_order() is called repeatly
changing the fract_leftover. Thus, the branch which is not dependent
on fract_leftover is executed repeatly. So make it run only once.

Plus, when min_object reached to 0, we set fract_leftover to 1.
In this case, we can calculate order by max(slub_min_order,
get_order(size) instead of calling calc_slab_order().

No functional impact expectd.

Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
---
 mm/slub.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index ed5c2c03a47a..e7a394d7b75a 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3795,9 +3795,6 @@ static inline unsigned int calc_slab_order(unsigned int size,
 	unsigned int min_order = slub_min_order;
 	unsigned int order;
 
-	if (order_objects(min_order, size) > MAX_OBJS_PER_PAGE)
-		return get_order(size * MAX_OBJS_PER_PAGE) - 1;
-
 	for (order = max(min_order, (unsigned int)get_order(min_objects * size));
 			order <= max_order; order++) {
 
@@ -3820,6 +3817,11 @@ static inline int calculate_order(unsigned int size)
 	unsigned int max_objects;
 	unsigned int nr_cpus;
 
+	if (unlikely(order_objects(slub_min_order, size) > MAX_OBJS_PER_PAGE)) {
+		order = get_order(size * MAX_OBJS_PER_PAGE) - 1;
+		goto out;
+	}
+
 	/*
 	 * Attempt to find best configuration for a slab. This
 	 * works by first attempting to generate a layout with
@@ -3865,14 +3867,8 @@ static inline int calculate_order(unsigned int size)
 	 * We were unable to place multiple objects in a slab. Now
 	 * lets see if we can place a single object there.
 	 */
-	order = calc_slab_order(size, 1, slub_max_order, 1);
-	if (order <= slub_max_order)
-		return order;
-
-	/*
-	 * Doh this slab cannot be placed using slub_max_order.
-	 */
-	order = calc_slab_order(size, 1, MAX_ORDER, 1);
+	order = max_t(unsigned int, slub_min_order, (unsigned int)get_order(size));
+out:
 	if (order < MAX_ORDER)
 		return order;
 	return -ENOSYS;
-- 
2.30.2