linux-kernel - [PATCH 2/2] mm, page_alloc: use unlikely() in task

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Date:   Tue, 16 Jun 2020 10:26:49 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     vbabka@...e.cz
Cc:     akpm@...ux-foundation.org, alex.shi@...ux.alibaba.com,
        hughd@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        liwang@...hat.com, mgorman@...hsingularity.net
Subject: [PATCH 2/2] mm, page_alloc: use unlikely() in task_capc()

Hugh noted that task_capc() could use unlikely(), as most of the time there is
no capture in progress and we are in page freeing hot path. Indeed adding
unlikely() redirects produces assembly that better matches the assumption and
moves all the tests away from the hot path.

I have also noticed that we don't need to test for cc->direct_compaction as the
only place we set current->task_capture is compact_zone_order() which also
always sets cc->direct_compaction true.

Suggested-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/page_alloc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 48eb0f1410d4..8a4e342d7e8f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -813,11 +813,10 @@ static inline struct capture_control *task_capc(struct zone *zone)
 {
 	struct capture_control *capc = current->capture_control;

-	return capc &&
+	return unlikely(capc &&
 		!(current->flags & PF_KTHREAD) &&
 		!capc->page &&
-		capc->cc->zone == zone &&
-		capc->cc->direct_compaction ? capc : NULL;
+		capc->cc->zone == zone) ? capc : NULL;
 }

 static inline bool
-- 
2.27.0