[PATCH 1/2] mm: vmpressure: don't need call kfree if kstrndup fails

[PATCH 1/2] mm: vmpressure: don't need call kfree if kstrndup fails

[Yang Shi]

When kstrndup fails (returns NULL) there is no memory is allocated by
kmalloc, so no need to call kfree().

Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
 mm/vmpressure.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 4bac22f..0590f00 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -371,10 +371,8 @@ int vmpressure_register_event(struct mem_cgroup *memcg,
 	int ret = 0;
 
 	spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
-	if (!spec) {
-		ret = -ENOMEM;
-		goto out;
-	}
+	if (!spec)
+		return -ENOMEM;
 
 	/* Find required level */
 	token = strsep(&spec, ",");
-- 
1.8.3.1

[PATCH 2/2] mm: vmpressure: use mem_cgroup_is_root API

[Yang Shi]

Use mem_cgroup_is_root() API to check if memcg is root memcg instead of
open coding.

Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
 mm/vmpressure.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 0590f00..d69019f 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -280,7 +280,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
 		enum vmpressure_levels level;
 
 		/* For now, no users for root-level efficiency */
-		if (!memcg || memcg == root_mem_cgroup)
+		if (!memcg || mem_cgroup_is_root(memcg))
 			return;
 
 		spin_lock(&vmpr->sr_lock);
-- 
1.8.3.1

Re: [PATCH 2/2] mm: vmpressure: use mem_cgroup_is_root API

[David Rientjes]

On Tue, 11 Feb 2020, Yang Shi wrote:

> Use mem_cgroup_is_root() API to check if memcg is root memcg instead of
> open coding.
> 
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Acked-by: David Rientjes <rientjes@google.com>

Re: [PATCH 2/2] mm: vmpressure: use mem_cgroup_is_root API

[Michal Hocko]

On Tue 11-02-20 13:24:09, Yang Shi wrote:
> Use mem_cgroup_is_root() API to check if memcg is root memcg instead of
> open coding.

Yes, the direct use outside of memcontrol.c should be really an
exception. The only other similar case is cgwb_bdi_init and there is no
easy way to replace - except for adding a helper which is not worth it.

> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  mm/vmpressure.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 0590f00..d69019f 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -280,7 +280,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
>  		enum vmpressure_levels level;
>  
>  		/* For now, no users for root-level efficiency */
> -		if (!memcg || memcg == root_mem_cgroup)
> +		if (!memcg || mem_cgroup_is_root(memcg))
>  			return;
>  
>  		spin_lock(&vmpr->sr_lock);
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs

Re: [PATCH 2/2] mm: vmpressure: use mem_cgroup_is_root API

[Yang Shi]

On 2/12/20 12:23 AM, Michal Hocko wrote:
> On Tue 11-02-20 13:24:09, Yang Shi wrote:
>> Use mem_cgroup_is_root() API to check if memcg is root memcg instead of
>> open coding.
> Yes, the direct use outside of memcontrol.c should be really an
> exception. The only other similar case is cgwb_bdi_init and there is no
> easy way to replace - except for adding a helper which is not worth it.

Yes, it seems so. cgwb_bdi_init just deferences root_mem_cgroup to 
access its css. It is the only user outside memcontrol.c, so I agree a 
helper for it might be overkilling. Once we have more users, it should 
be considered.

>
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks.

>
> Thanks!
>
>> ---
>>   mm/vmpressure.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
>> index 0590f00..d69019f 100644
>> --- a/mm/vmpressure.c
>> +++ b/mm/vmpressure.c
>> @@ -280,7 +280,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
>>   		enum vmpressure_levels level;
>>   
>>   		/* For now, no users for root-level efficiency */
>> -		if (!memcg || memcg == root_mem_cgroup)
>> +		if (!memcg || mem_cgroup_is_root(memcg))
>>   			return;
>>   
>>   		spin_lock(&vmpr->sr_lock);
>> -- 
>> 1.8.3.1
>>

Re: [PATCH 2/2] mm: vmpressure: use mem_cgroup_is_root API

[David Hildenbrand]

On 11.02.20 06:24, Yang Shi wrote:
> Use mem_cgroup_is_root() API to check if memcg is root memcg instead of
> open coding.
> 
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> ---
>  mm/vmpressure.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 0590f00..d69019f 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -280,7 +280,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
>  		enum vmpressure_levels level;
>  
>  		/* For now, no users for root-level efficiency */
> -		if (!memcg || memcg == root_mem_cgroup)
> +		if (!memcg || mem_cgroup_is_root(memcg))
>  			return;
>  
>  		spin_lock(&vmpr->sr_lock);
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb

Re: [PATCH 1/2] mm: vmpressure: don't need call kfree if kstrndup fails

[David Rientjes]

On Tue, 11 Feb 2020, Yang Shi wrote:

> When kstrndup fails (returns NULL) there is no memory is allocated by
> kmalloc, so no need to call kfree().
> 
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Acked-by: David Rientjes <rientjes@google.com>

Re: [PATCH 1/2] mm: vmpressure: don't need call kfree if kstrndup fails

[David Hildenbrand]

On 11.02.20 06:24, Yang Shi wrote:
> When kstrndup fails (returns NULL) there is no memory is allocated by
> kmalloc, so no need to call kfree().

"When kstrndup fails, no memory was allocated and we can exit directly."

Reviewed-by: David Hildenbrand <david@redhat.com>

> 
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> ---
>  mm/vmpressure.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 4bac22f..0590f00 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -371,10 +371,8 @@ int vmpressure_register_event(struct mem_cgroup *memcg,
>  	int ret = 0;
>  
>  	spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
> -	if (!spec) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> +	if (!spec)
> +		return -ENOMEM;
>  
>  	/* Find required level */
>  	token = strsep(&spec, ",");
> 


-- 
Thanks,

David / dhildenb

Re: [PATCH 1/2] mm: vmpressure: don't need call kfree if kstrndup fails

[Yang Shi]

On 2/12/20 3:21 AM, David Hildenbrand wrote:
> On 11.02.20 06:24, Yang Shi wrote:
>> When kstrndup fails (returns NULL) there is no memory is allocated by
>> kmalloc, so no need to call kfree().
> "When kstrndup fails, no memory was allocated and we can exit directly."

Thanks for correcting the commit log.

Andrew, do you prefer I send an updated version or you would just update 
the patch in -mm tree?

>
> Reviewed-by: David Hildenbrand <david@redhat.com>
>
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>> ---
>>   mm/vmpressure.c | 6 ++----
>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
>> index 4bac22f..0590f00 100644
>> --- a/mm/vmpressure.c
>> +++ b/mm/vmpressure.c
>> @@ -371,10 +371,8 @@ int vmpressure_register_event(struct mem_cgroup *memcg,
>>   	int ret = 0;
>>   
>>   	spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
>> -	if (!spec) {
>> -		ret = -ENOMEM;
>> -		goto out;
>> -	}
>> +	if (!spec)
>> +		return -ENOMEM;
>>   
>>   	/* Find required level */
>>   	token = strsep(&spec, ",");
>>
>

Re: [PATCH 1/2] mm: vmpressure: don't need call kfree if kstrndup fails

[Andrew Morton]

On Wed, 12 Feb 2020 19:14:27 -0800 Yang Shi <yang.shi@linux.alibaba.com> wrote:

> On 2/12/20 3:21 AM, David Hildenbrand wrote:
> > On 11.02.20 06:24, Yang Shi wrote:
> >> When kstrndup fails (returns NULL) there is no memory is allocated by
> >> kmalloc, so no need to call kfree().
> > "When kstrndup fails, no memory was allocated and we can exit directly."
> 
> Thanks for correcting the commit log.
> 
> Andrew, do you prefer I send an updated version or you would just update 
> the patch in -mm tree?

I have already done this.

From: Yang Shi <yang.shi@linux.alibaba.com>
Subject: mm: vmpressure: don't need call kfree if kstrndup fails

When kstrndup fails, no memory was allocated and we can exit directly.

[david@redhat.com: reword changelog]
Link: http://lkml.kernel.org/r/1581398649-125989-1-git-send-email-yang.shi@linux.alibaba.com
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmpressure.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/mm/vmpressure.c~mm-vmpressure-dont-need-call-kfree-if-kstrndup-fails
+++ a/mm/vmpressure.c
@@ -371,10 +371,8 @@ int vmpressure_register_event(struct mem
 	int ret = 0;
 
 	spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
-	if (!spec) {
-		ret = -ENOMEM;
-		goto out;
-	}
+	if (!spec)
+		return -ENOMEM;
 
 	/* Find required level */
 	token = strsep(&spec, ",");
_

Re: [PATCH 1/2] mm: vmpressure: don't need call kfree if kstrndup fails

[Yang Shi]

On 2/12/20 8:48 PM, Andrew Morton wrote:
> On Wed, 12 Feb 2020 19:14:27 -0800 Yang Shi <yang.shi@linux.alibaba.com> wrote:
>
>> On 2/12/20 3:21 AM, David Hildenbrand wrote:
>>> On 11.02.20 06:24, Yang Shi wrote:
>>>> When kstrndup fails (returns NULL) there is no memory is allocated by
>>>> kmalloc, so no need to call kfree().
>>> "When kstrndup fails, no memory was allocated and we can exit directly."
>> Thanks for correcting the commit log.
>>
>> Andrew, do you prefer I send an updated version or you would just update
>> the patch in -mm tree?
> I have already done this.

Thanks!

>
> From: Yang Shi <yang.shi@linux.alibaba.com>
> Subject: mm: vmpressure: don't need call kfree if kstrndup fails
>
> When kstrndup fails, no memory was allocated and we can exit directly.
>
> [david@redhat.com: reword changelog]
> Link: http://lkml.kernel.org/r/1581398649-125989-1-git-send-email-yang.shi@linux.alibaba.com
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Acked-by: David Rientjes <rientjes@google.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
>   mm/vmpressure.c |    6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> --- a/mm/vmpressure.c~mm-vmpressure-dont-need-call-kfree-if-kstrndup-fails
> +++ a/mm/vmpressure.c
> @@ -371,10 +371,8 @@ int vmpressure_register_event(struct mem
>   	int ret = 0;
>   
>   	spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
> -	if (!spec) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> +	if (!spec)
> +		return -ENOMEM;
>   
>   	/* Find required level */
>   	token = strsep(&spec, ",");
> _