linux-kernel - [PATCH] mm/mremap_pages: Save a few cycles in 'get_dev

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Message-Id: <b4a47154877853cc64be3a35dcfd594d40cc2bce.1635975283.git.christophe.jaillet@wanadoo.fr>
Date:   Wed,  3 Nov 2021 22:35:34 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH] mm/mremap_pages: Save a few cycles in 'get_dev_pagemap()'

Use 'percpu_ref_tryget_live_rcu()' instead of 'percpu_ref_tryget_live()' to
save a few cycles when it is known that the rcu lock is already
taken/released.

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
 mm/memremap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memremap.c b/mm/memremap.c
index 84de22c14567..012e8d23d365 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -506,7 +506,7 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
 	/* fall back to slow path lookup */
 	rcu_read_lock();
 	pgmap = xa_load(&pgmap_array, PHYS_PFN(phys));
-	if (pgmap && !percpu_ref_tryget_live(pgmap->ref))
+	if (pgmap && !percpu_ref_tryget_live_rcu(pgmap->ref))
 		pgmap = NULL;
 	rcu_read_unlock();
 
-- 
2.30.2