linux-kernel - [PATCH 2/2] mm/vmalloc: Use __this_cpu_try_cmpxchg() in preload_this_cpu

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Message-ID: <20240523080136.9863-2-ubizjak@gmail.com>
Date: Thu, 23 May 2024 10:00:32 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Lorenzo Stoakes <lstoakes@...il.com>,
	Dennis Zhou <dennis@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux.com>
Subject: [PATCH 2/2] mm/vmalloc: Use __this_cpu_try_cmpxchg() in preload_this_cpu_lock()

Use __this_cpu_try_cmpxchg() instead of
__this_cpu_cmpxchg (*ptr, old, new) == old in
preload_this_cpu_lock().  x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Uladzislau Rezki <urezki@...il.com>
Cc: Christoph Hellwig <hch@...radead.org>
Cc: Lorenzo Stoakes <lstoakes@...il.com>
Cc: Dennis Zhou <dennis@...nel.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: Christoph Lameter <cl@...ux.com>
---
 mm/vmalloc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 6641be0ca80b..0120faee5471 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1816,7 +1816,7 @@ static void free_vmap_area(struct vmap_area *va)
 static inline void
 preload_this_cpu_lock(spinlock_t *lock, gfp_t gfp_mask, int node)
 {
-	struct vmap_area *va = NULL;
+	struct vmap_area *va = NULL, *tmp;
 
 	/*
 	 * Preload this CPU with one extra vmap_area object. It is used
@@ -1832,7 +1832,8 @@ preload_this_cpu_lock(spinlock_t *lock, gfp_t gfp_mask, int node)
 
 	spin_lock(lock);
 
-	if (va && __this_cpu_cmpxchg(ne_fit_preload_node, NULL, va))
+	tmp = NULL;
+	if (va && !__this_cpu_try_cmpxchg(ne_fit_preload_node, &tmp, va))
 		kmem_cache_free(vmap_area_cachep, va);
 }
 
-- 
2.45.1