linux-kernel - [tip: sched/psi] devres: Slightly optimize alloc

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Date:   Fri, 09 Sep 2022 14:00:20 -0000
From:   "tip-bot2 for Christophe JAILLET" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/psi] devres: Slightly optimize alloc_dr()

The following commit has been merged into the sched/psi branch of tip:

Commit-ID:     61742a7cd5b194d2cc52d78de8ec6967634a4cd6
Gitweb:        https://git.kernel.org/tip/61742a7cd5b194d2cc52d78de8ec6967634a4cd6
Author:        Christophe JAILLET <christophe.jaillet@...adoo.fr>
AuthorDate:    Wed, 20 Jul 2022 23:26:36 +02:00
Committer:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CommitterDate: Thu, 01 Sep 2022 18:17:14 +02:00

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>
Link: https://lore.kernel.org/r/d255bd871484e63cdd628e819f929e2df59afb02.1658352383.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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 864d0b3..4ab2b50 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;