[PATCH v2 1/2] percpu: Add __this_cpu_try_cmpxchg()

[PATCH v2 1/2] percpu: Add __this_cpu_try_cmpxchg()

[Uros Bizjak]

Add __this_cpu_try_cmpxchg() version of the percpu op.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
---
 include/linux/percpu-defs.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
index ec3573119923..8efce7414fad 100644
--- a/include/linux/percpu-defs.h
+++ b/include/linux/percpu-defs.h
@@ -475,6 +475,12 @@ do {									\
 	raw_cpu_cmpxchg(pcp, oval, nval);				\
 })
 
+#define __this_cpu_try_cmpxchg(pcp, ovalp, nval)			\
+({									\
+	__this_cpu_preempt_check("try_cmpxchg");			\
+	raw_cpu_try_cmpxchg(pcp, ovalp, nval);				\
+})
+
 #define __this_cpu_sub(pcp, val)	__this_cpu_add(pcp, -(typeof(pcp))(val))
 #define __this_cpu_inc(pcp)		__this_cpu_add(pcp, 1)
 #define __this_cpu_dec(pcp)		__this_cpu_sub(pcp, 1)
-- 
2.42.0

[PATCH v2 2/2] mm/vmalloc: Use __this_cpu_try_cmpxchg() in preload_this_cpu_lock()

[Uros Bizjak]

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.

The generated code improves from:

    4bb6:	48 85 f6             	test   %rsi,%rsi
    4bb9:	0f 84 10 fa ff ff    	je     45cf <...>
    4bbf:	4c 89 e8             	mov    %r13,%rax
    4bc2:	65 48 0f b1 35 00 00 	cmpxchg %rsi,%gs:0x0(%rip)
    4bc9:	00 00
    4bcb:	48 85 c0             	test   %rax,%rax
    4bce:	0f 84 fb f9 ff ff    	je     45cf <...>

to:

    4bb6:	48 85 f6             	test   %rsi,%rsi
    4bb9:	0f 84 10 fa ff ff    	je     45cf <...>
    4bbf:	4c 89 e8             	mov    %r13,%rax
    4bc2:	65 48 0f b1 35 00 00 	cmpxchg %rsi,%gs:0x0(%rip)
    4bc9:	00 00
    4bcb:	0f 84 fe f9 ff ff    	je     45cf <...>

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
---
v2: Show generated code improvement in the commit message.
---
 mm/vmalloc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5d3aa2dc88a8..4f34d935d648 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);
 }
 
-- 
2.42.0

Re: [PATCH v2 2/2] mm/vmalloc: Use __this_cpu_try_cmpxchg() in preload_this_cpu_lock()

[Uladzislau Rezki]

On Tue, May 28, 2024 at 04:43:14PM +0200, Uros Bizjak wrote:
> 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.
> 
> The generated code improves from:
> 
>     4bb6:	48 85 f6             	test   %rsi,%rsi
>     4bb9:	0f 84 10 fa ff ff    	je     45cf <...>
>     4bbf:	4c 89 e8             	mov    %r13,%rax
>     4bc2:	65 48 0f b1 35 00 00 	cmpxchg %rsi,%gs:0x0(%rip)
>     4bc9:	00 00
>     4bcb:	48 85 c0             	test   %rax,%rax
>     4bce:	0f 84 fb f9 ff ff    	je     45cf <...>
> 
> to:
> 
>     4bb6:	48 85 f6             	test   %rsi,%rsi
>     4bb9:	0f 84 10 fa ff ff    	je     45cf <...>
>     4bbf:	4c 89 e8             	mov    %r13,%rax
>     4bc2:	65 48 0f b1 35 00 00 	cmpxchg %rsi,%gs:0x0(%rip)
>     4bc9:	00 00
>     4bcb:	0f 84 fe f9 ff ff    	je     45cf <...>
> 
> No functional change intended.
> 
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Uladzislau Rezki <urezki@gmail.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Lorenzo Stoakes <lstoakes@gmail.com>
> Cc: Dennis Zhou <dennis@kernel.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Christoph Lameter <cl@linux.com>
> ---
> v2: Show generated code improvement in the commit message.
> ---
>  mm/vmalloc.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 5d3aa2dc88a8..4f34d935d648 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);
>  }
>  
> -- 
> 2.42.0
> 
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

Thanks!

--
Uladzislau Rezki

Re: [PATCH v2 1/2] percpu: Add __this_cpu_try_cmpxchg()

[Uladzislau Rezki]

On Tue, May 28, 2024 at 04:43:13PM +0200, Uros Bizjak wrote:
> Add __this_cpu_try_cmpxchg() version of the percpu op.
> 
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Uladzislau Rezki <urezki@gmail.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Lorenzo Stoakes <lstoakes@gmail.com>
> Cc: Dennis Zhou <dennis@kernel.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Christoph Lameter <cl@linux.com>
> ---
>  include/linux/percpu-defs.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
> index ec3573119923..8efce7414fad 100644
> --- a/include/linux/percpu-defs.h
> +++ b/include/linux/percpu-defs.h
> @@ -475,6 +475,12 @@ do {									\
>  	raw_cpu_cmpxchg(pcp, oval, nval);				\
>  })
>  
> +#define __this_cpu_try_cmpxchg(pcp, ovalp, nval)			\
> +({									\
> +	__this_cpu_preempt_check("try_cmpxchg");			\
> +	raw_cpu_try_cmpxchg(pcp, ovalp, nval);				\
> +})
> +
>  #define __this_cpu_sub(pcp, val)	__this_cpu_add(pcp, -(typeof(pcp))(val))
>  #define __this_cpu_inc(pcp)		__this_cpu_add(pcp, 1)
>  #define __this_cpu_dec(pcp)		__this_cpu_sub(pcp, 1)
> -- 
> 2.42.0
> 
Acked-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

Thanks!

--
Uladzislau Rezki