linux-kernel - [PATCH] devres: Slightly optimize alloc

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Message-Id: <d255bd871484e63cdd628e819f929e2df59afb02.1658352383.git.christophe.jaillet@wanadoo.fr>
Date:   Wed, 20 Jul 2022 23:26:36 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH] devres: Slightly optimize alloc_dr()

If the gfp flag used for the memory allocation already has __GFP_ZERO,
then there is no need to explicitly clear the "struct devres_node". It is
already zeroed.

This saves a few cycles when using devm_zalloc() and co.

In the case of devres_alloc() (which calls __devres_alloc_node()), the
compiler could remove the test and the memset() because it should be able
to see that the __GFP_ZERO flag is set.
So this would make the code both faster and smaller.

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
 drivers/base/devres.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index 864d0b3f566e..4ab2b50ee38f 100644
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -117,7 +117,9 @@ static __always_inline struct devres * alloc_dr(dr_release_t release,
 	if (unlikely(!dr))
 		return NULL;
 
-	memset(dr, 0, offsetof(struct devres, data));
+	/* No need to clear memory twice */
+	if (!(gfp & __GFP_ZERO))
+		memset(dr, 0, offsetof(struct devres, data));
 
 	INIT_LIST_HEAD(&dr->node.entry);
 	dr->node.release = release;
-- 
2.34.1