[PATCH 0/3] clean up some functions in mm/swap_slots.c

[PATCH 0/3] clean up some functions in mm/swap_slots.c

[Zhen Lei]

When I studied the code of mm/swap_slots.c, I found some places can be improved.

Zhen Lei (3):
  mm/swap: simplify alloc_swap_slot_cache()
  mm/swap: simplify enable_swap_slots_cache()
  mm/swap: remove redundant check for swap_slot_cache_initialized

 mm/swap_slots.c | 45 +++++++++++++++++++++------------------------
 1 file changed, 21 insertions(+), 24 deletions(-)

-- 
2.26.0.106.g9fadedd

[PATCH 1/3] mm/swap: simplify alloc_swap_slot_cache()

[Zhen Lei]

Both "slots" and "slots_ret" are only need to be freed when cache already
allocated. Make them closer, seems more clear.

No functional change.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 mm/swap_slots.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index 0975adc72253..01609b5f0c55 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -136,9 +136,16 @@ static int alloc_swap_slot_cache(unsigned int cpu)
 
 	mutex_lock(&swap_slots_cache_mutex);
 	cache = &per_cpu(swp_slots, cpu);
-	if (cache->slots || cache->slots_ret)
+	if (cache->slots || cache->slots_ret) {
 		/* cache already allocated */
-		goto out;
+		mutex_unlock(&swap_slots_cache_mutex);
+
+		kvfree(slots);
+		kvfree(slots_ret);
+
+		return 0;
+	}
+
 	if (!cache->lock_initialized) {
 		mutex_init(&cache->alloc_lock);
 		spin_lock_init(&cache->free_lock);
@@ -155,15 +162,8 @@ static int alloc_swap_slot_cache(unsigned int cpu)
 	 */
 	mb();
 	cache->slots = slots;
-	slots = NULL;
 	cache->slots_ret = slots_ret;
-	slots_ret = NULL;
-out:
 	mutex_unlock(&swap_slots_cache_mutex);
-	if (slots)
-		kvfree(slots);
-	if (slots_ret)
-		kvfree(slots_ret);
 	return 0;
 }
 
-- 
2.26.0.106.g9fadedd

[PATCH 2/3] mm/swap: simplify enable_swap_slots_cache()

[Zhen Lei]

Whether swap_slot_cache_initialized is true or false,
__reenable_swap_slots_cache() is always called. To make this meaning
clear, leave only one call to __reenable_swap_slots_cache(). This also
make it clearer what extra needs be done when swap_slot_cache_initialized
is false.

No functional change.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 mm/swap_slots.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index 01609b5f0c55..b40394473a3c 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -240,21 +240,19 @@ static int free_slot_cache(unsigned int cpu)
 
 int enable_swap_slots_cache(void)
 {
-	int ret = 0;
-
 	mutex_lock(&swap_slots_cache_enable_mutex);
-	if (swap_slot_cache_initialized) {
-		__reenable_swap_slots_cache();
-		goto out_unlock;
-	}
+	if (!swap_slot_cache_initialized) {
+		int ret;
 
-	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
-				alloc_swap_slot_cache, free_slot_cache);
-	if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
-			       "without swap slots cache.\n", __func__))
-		goto out_unlock;
+		ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
+					alloc_swap_slot_cache, free_slot_cache);
+		if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
+				       "without swap slots cache.\n", __func__))
+			goto out_unlock;
+
+		swap_slot_cache_initialized = true;
+	}
 
-	swap_slot_cache_initialized = true;
 	__reenable_swap_slots_cache();
 out_unlock:
 	mutex_unlock(&swap_slots_cache_enable_mutex);
-- 
2.26.0.106.g9fadedd

[PATCH 3/3] mm/swap: remove redundant check for swap_slot_cache_initialized

[Zhen Lei]

Because enable_swap_slots_cache can only become true in
enable_swap_slots_cache(), and depends on swap_slot_cache_initialized is
true before. That means, when enable_swap_slots_cache is true,
swap_slot_cache_initialized is true also.

So the condition:
"swap_slot_cache_enabled && swap_slot_cache_initialized"
can be reduced to "swap_slot_cache_enabled"

And in mathematics:
"!swap_slot_cache_enabled || !swap_slot_cache_initialized"
is equal to "!(swap_slot_cache_enabled && swap_slot_cache_initialized)"

So no functional change.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 mm/swap_slots.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index b40394473a3c..3e6453573a89 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -46,8 +46,7 @@ static void __drain_swap_slots_cache(unsigned int type);
 static void deactivate_swap_slots_cache(void);
 static void reactivate_swap_slots_cache(void);
 
-#define use_swap_slot_cache (swap_slot_cache_active && \
-		swap_slot_cache_enabled && swap_slot_cache_initialized)
+#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)
 #define SLOTS_CACHE 0x1
 #define SLOTS_CACHE_RET 0x2
 
@@ -94,7 +93,7 @@ static bool check_cache_active(void)
 {
 	long pages;
 
-	if (!swap_slot_cache_enabled || !swap_slot_cache_initialized)
+	if (!swap_slot_cache_enabled)
 		return false;
 
 	pages = get_nr_swap_pages();
-- 
2.26.0.106.g9fadedd

Re: [PATCH 1/3] mm/swap: simplify alloc_swap_slot_cache()

[Tim Chen]

On 4/29/20 11:11 PM, Zhen Lei wrote:
> Both "slots" and "slots_ret" are only need to be freed when cache already
> allocated. Make them closer, seems more clear.
> 
> No functional change.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> ---
>  mm/swap_slots.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/swap_slots.c b/mm/swap_slots.c
> index 0975adc72253..01609b5f0c55 100644
> --- a/mm/swap_slots.c
> +++ b/mm/swap_slots.c
> @@ -136,9 +136,16 @@ static int alloc_swap_slot_cache(unsigned int cpu)
>  
>  	mutex_lock(&swap_slots_cache_mutex);
>  	cache = &per_cpu(swp_slots, cpu);
> -	if (cache->slots || cache->slots_ret)
> +	if (cache->slots || cache->slots_ret) {
>  		/* cache already allocated */
> -		goto out;
> +		mutex_unlock(&swap_slots_cache_mutex);
> +
> +		kvfree(slots);
> +		kvfree(slots_ret);
> +
> +		return 0;
> +	}
> +
>  	if (!cache->lock_initialized) {
>  		mutex_init(&cache->alloc_lock);
>  		spin_lock_init(&cache->free_lock);
> @@ -155,15 +162,8 @@ static int alloc_swap_slot_cache(unsigned int cpu)
>  	 */
>  	mb();
>  	cache->slots = slots;
> -	slots = NULL;
>  	cache->slots_ret = slots_ret;
> -	slots_ret = NULL;
> -out:
>  	mutex_unlock(&swap_slots_cache_mutex);
> -	if (slots)
> -		kvfree(slots);
> -	if (slots_ret)
> -		kvfree(slots_ret);
>  	return 0;
>  }
>  
> 

Acked-by: Tim Chen <tim.c.chen@linux.intel.com>

Re: [PATCH 2/3] mm/swap: simplify enable_swap_slots_cache()

[Tim Chen]

On 4/29/20 11:11 PM, Zhen Lei wrote:
> Whether swap_slot_cache_initialized is true or false,
> __reenable_swap_slots_cache() is always called. To make this meaning
> clear, leave only one call to __reenable_swap_slots_cache(). This also
> make it clearer what extra needs be done when swap_slot_cache_initialized
> is false.
> 
> No functional change.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>

Acked-by: Tim Chen <tim.c.chen@linux.intel.com>

> ---
>  mm/swap_slots.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/swap_slots.c b/mm/swap_slots.c
> index 01609b5f0c55..b40394473a3c 100644
> --- a/mm/swap_slots.c
> +++ b/mm/swap_slots.c
> @@ -240,21 +240,19 @@ static int free_slot_cache(unsigned int cpu)
>  
>  int enable_swap_slots_cache(void)
>  {
> -	int ret = 0;
> -
>  	mutex_lock(&swap_slots_cache_enable_mutex);
> -	if (swap_slot_cache_initialized) {
> -		__reenable_swap_slots_cache();
> -		goto out_unlock;
> -	}
> +	if (!swap_slot_cache_initialized) {
> +		int ret;
>  
> -	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
> -				alloc_swap_slot_cache, free_slot_cache);
> -	if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
> -			       "without swap slots cache.\n", __func__))
> -		goto out_unlock;
> +		ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
> +					alloc_swap_slot_cache, free_slot_cache);
> +		if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
> +				       "without swap slots cache.\n", __func__))
> +			goto out_unlock;
> +
> +		swap_slot_cache_initialized = true;
> +	}
>  
> -	swap_slot_cache_initialized = true;
>  	__reenable_swap_slots_cache();
>  out_unlock:
>  	mutex_unlock(&swap_slots_cache_enable_mutex);
> 

Re: [PATCH 3/3] mm/swap: remove redundant check for swap_slot_cache_initialized

[Tim Chen]

On 4/29/20 11:11 PM, Zhen Lei wrote:
> Because enable_swap_slots_cache can only become true in
> enable_swap_slots_cache(), and depends on swap_slot_cache_initialized is
> true before. That means, when enable_swap_slots_cache is true,
> swap_slot_cache_initialized is true also.
> 
> So the condition:
> "swap_slot_cache_enabled && swap_slot_cache_initialized"
> can be reduced to "swap_slot_cache_enabled"
> 
> And in mathematics:
> "!swap_slot_cache_enabled || !swap_slot_cache_initialized"
> is equal to "!(swap_slot_cache_enabled && swap_slot_cache_initialized)"
> 
> So no functional change.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> ---
>  mm/swap_slots.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/swap_slots.c b/mm/swap_slots.c
> index b40394473a3c..3e6453573a89 100644
> --- a/mm/swap_slots.c
> +++ b/mm/swap_slots.c
> @@ -46,8 +46,7 @@ static void __drain_swap_slots_cache(unsigned int type);
>  static void deactivate_swap_slots_cache(void);
>  static void reactivate_swap_slots_cache(void);
>  
> -#define use_swap_slot_cache (swap_slot_cache_active && \
> -		swap_slot_cache_enabled && swap_slot_cache_initialized)
> +#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)

Yes, swap_slot_cache_enabled does imply swap_slot_cache_initialized
in current code.  So checking swap_slot_cache_enabled is
enough here.

>  #define SLOTS_CACHE 0x1
>  #define SLOTS_CACHE_RET 0x2
>  
> @@ -94,7 +93,7 @@ static bool check_cache_active(void)
>  {
>  	long pages;
>  
> -	if (!swap_slot_cache_enabled || !swap_slot_cache_initialized)
> +	if (!swap_slot_cache_enabled)

This simplification is okay.   !swap_slot_cache_initialize implies !swap_slot_cache_enabled.
So only !swap_slot_cache_enabled needs to be checked.

>  		return false;
>  
>  	pages = get_nr_swap_pages();
> 

Acked-by: Tim Chen <tim.c.chen@linux.intel.com>

Re: [PATCH 0/3] clean up some functions in mm/swap_slots.c

[Leizhen (ThunderTown)]

Hi, all:
  Are these patches acceptable？
  All these three patches are "Acked-by: Tim Chen <tim.c.chen@linux.intel.com>" two months ago.

On 2020/4/30 14:11, Zhen Lei wrote:
> When I studied the code of mm/swap_slots.c, I found some places can be improved.
> 
> Zhen Lei (3):
>   mm/swap: simplify alloc_swap_slot_cache()
>   mm/swap: simplify enable_swap_slots_cache()
>   mm/swap: remove redundant check for swap_slot_cache_initialized
> 
>  mm/swap_slots.c | 45 +++++++++++++++++++++------------------------
>  1 file changed, 21 insertions(+), 24 deletions(-)
>