linux-kernel - [PATCH v2] mm/mremap_pages: Save a few cycles in get_dev

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Message-Id: <9ef1562a1975371360f3e263856e9f1c5749b656.1662136782.git.christophe.jaillet@wanadoo.fr>
Date:   Fri,  2 Sep 2022 18:39:52 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        linux-mm@...ck.org
Subject: [PATCH v2] 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>
---
Matthew Wilcox <willy@...radead.org> commented on v1 that it is just a slow
path... but it is also just an easy patch :)

If considered as useless, let me know and I'll drop it from my WIP list.

Changes in v2:
  * (no code change)
  * synch with latest -next

v1:
  https://lore.kernel.org/all/b4a47154877853cc64be3a35dcfd594d40cc2bce.1635975283.git.christophe.jaillet@wanadoo.fr/
---
 mm/memremap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memremap.c b/mm/memremap.c
index 58b20c3c300b..25029a474d30 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -454,7 +454,7 @@ 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();
 
-- 
2.34.1