Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-08-17 Thread Mel Gorman 
On Wed, Aug 12, 2015 at 05:16:50PM -0700, David Rientjes wrote:
> On Wed, 12 Aug 2015, Mel Gorman wrote:
> 
> > There is a seqcounter that protects against spurious allocation failures
> > when a task is changing the allowed nodes in a cpuset. There is no need
> > to check the seqcounter until a cpuset exists.
> > 
> > Signed-off-by: Mel Gorman 
> > Acked-by: David Rientjes 
> > Acked-by: Vlastimil Babka 
> > ---
> >  include/linux/cpuset.h | 6 ++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> > index 1b357997cac5..6eb27cb480b7 100644
> > --- a/include/linux/cpuset.h
> > +++ b/include/linux/cpuset.h
> > @@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
> > task_struct *p);
> >   */
> >  static inline unsigned int read_mems_allowed_begin(void)
> >  {
> > +   if (!cpusets_enabled())
> > +   return 0;
> > +
> > return read_seqcount_begin(>mems_allowed_seq);
> >  }
> >  
> > @@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
> >   */
> >  static inline bool read_mems_allowed_retry(unsigned int seq)
> >  {
> > +   if (!cpusets_enabled())
> > +   return false;
> > +
> > return read_seqcount_retry(>mems_allowed_seq, seq);
> >  }
> >  
> 
> This patch is an obvious improvement, but I think it's also possible to 
> change this to be
> 
>   if (nr_cpusets() <= 1)
>   return false;
> 
> and likewise in the existing cpusets_enabled() check in 
> get_page_from_freelist().  A root cpuset may not exclude mems on the 
> system so, even if mounted, there's no need to check or be worried about 
> concurrent change when there is only one cpuset.

Good idea. I'll make this a separate patch on top and rename cpuset_enabled
to cpuset_mems_enabled to be clear about what it's checking.

Thanks.

-- 
Mel Gorman
SUSE Labs
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Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-08-17 Thread Mel Gorman 
On Wed, Aug 12, 2015 at 05:16:50PM -0700, David Rientjes wrote:
 On Wed, 12 Aug 2015, Mel Gorman wrote:
 
  There is a seqcounter that protects against spurious allocation failures
  when a task is changing the allowed nodes in a cpuset. There is no need
  to check the seqcounter until a cpuset exists.
  
  Signed-off-by: Mel Gorman mgor...@techsingularity.net
  Acked-by: David Rientjes rient...@google.com
  Acked-by: Vlastimil Babka vba...@suse.cz
  ---
   include/linux/cpuset.h | 6 ++
   1 file changed, 6 insertions(+)
  
  diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
  index 1b357997cac5..6eb27cb480b7 100644
  --- a/include/linux/cpuset.h
  +++ b/include/linux/cpuset.h
  @@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
  task_struct *p);
*/
   static inline unsigned int read_mems_allowed_begin(void)
   {
  +   if (!cpusets_enabled())
  +   return 0;
  +
  return read_seqcount_begin(current-mems_allowed_seq);
   }
   
  @@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
*/
   static inline bool read_mems_allowed_retry(unsigned int seq)
   {
  +   if (!cpusets_enabled())
  +   return false;
  +
  return read_seqcount_retry(current-mems_allowed_seq, seq);
   }
   
 
 This patch is an obvious improvement, but I think it's also possible to 
 change this to be
 
   if (nr_cpusets() = 1)
   return false;
 
 and likewise in the existing cpusets_enabled() check in 
 get_page_from_freelist().  A root cpuset may not exclude mems on the 
 system so, even if mounted, there's no need to check or be worried about 
 concurrent change when there is only one cpuset.

Good idea. I'll make this a separate patch on top and rename cpuset_enabled
to cpuset_mems_enabled to be clear about what it's checking.

Thanks.

-- 
Mel Gorman
SUSE Labs
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Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-08-12 Thread David Rientjes 
On Wed, 12 Aug 2015, Mel Gorman wrote:

> There is a seqcounter that protects against spurious allocation failures
> when a task is changing the allowed nodes in a cpuset. There is no need
> to check the seqcounter until a cpuset exists.
> 
> Signed-off-by: Mel Gorman 
> Acked-by: David Rientjes 
> Acked-by: Vlastimil Babka 
> ---
>  include/linux/cpuset.h | 6 ++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index 1b357997cac5..6eb27cb480b7 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
> task_struct *p);
>   */
>  static inline unsigned int read_mems_allowed_begin(void)
>  {
> + if (!cpusets_enabled())
> + return 0;
> +
>   return read_seqcount_begin(>mems_allowed_seq);
>  }
>  
> @@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
>   */
>  static inline bool read_mems_allowed_retry(unsigned int seq)
>  {
> + if (!cpusets_enabled())
> + return false;
> +
>   return read_seqcount_retry(>mems_allowed_seq, seq);
>  }
>  

This patch is an obvious improvement, but I think it's also possible to 
change this to be

if (nr_cpusets() <= 1)
return false;

and likewise in the existing cpusets_enabled() check in 
get_page_from_freelist().  A root cpuset may not exclude mems on the 
system so, even if mounted, there's no need to check or be worried about 
concurrent change when there is only one cpuset.
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[PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-08-12 Thread Mel Gorman 
There is a seqcounter that protects against spurious allocation failures
when a task is changing the allowed nodes in a cpuset. There is no need
to check the seqcounter until a cpuset exists.

Signed-off-by: Mel Gorman 
Acked-by: David Rientjes 
Acked-by: Vlastimil Babka 
---
 include/linux/cpuset.h | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 1b357997cac5..6eb27cb480b7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
task_struct *p);
  */
 static inline unsigned int read_mems_allowed_begin(void)
 {
+   if (!cpusets_enabled())
+   return 0;
+
return read_seqcount_begin(>mems_allowed_seq);
 }
 
@@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
  */
 static inline bool read_mems_allowed_retry(unsigned int seq)
 {
+   if (!cpusets_enabled())
+   return false;
+
return read_seqcount_retry(>mems_allowed_seq, seq);
 }
 
-- 
2.4.6

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Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-08-12 Thread David Rientjes 
On Wed, 12 Aug 2015, Mel Gorman wrote:

 There is a seqcounter that protects against spurious allocation failures
 when a task is changing the allowed nodes in a cpuset. There is no need
 to check the seqcounter until a cpuset exists.
 
 Signed-off-by: Mel Gorman mgor...@techsingularity.net
 Acked-by: David Rientjes rient...@google.com
 Acked-by: Vlastimil Babka vba...@suse.cz
 ---
  include/linux/cpuset.h | 6 ++
  1 file changed, 6 insertions(+)
 
 diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
 index 1b357997cac5..6eb27cb480b7 100644
 --- a/include/linux/cpuset.h
 +++ b/include/linux/cpuset.h
 @@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
 task_struct *p);
   */
  static inline unsigned int read_mems_allowed_begin(void)
  {
 + if (!cpusets_enabled())
 + return 0;
 +
   return read_seqcount_begin(current-mems_allowed_seq);
  }
  
 @@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
   */
  static inline bool read_mems_allowed_retry(unsigned int seq)
  {
 + if (!cpusets_enabled())
 + return false;
 +
   return read_seqcount_retry(current-mems_allowed_seq, seq);
  }
  

This patch is an obvious improvement, but I think it's also possible to 
change this to be

if (nr_cpusets() = 1)
return false;

and likewise in the existing cpusets_enabled() check in 
get_page_from_freelist().  A root cpuset may not exclude mems on the 
system so, even if mounted, there's no need to check or be worried about 
concurrent change when there is only one cpuset.
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
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Please read the FAQ at  http://www.tux.org/lkml/

[PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-08-12 Thread Mel Gorman 
There is a seqcounter that protects against spurious allocation failures
when a task is changing the allowed nodes in a cpuset. There is no need
to check the seqcounter until a cpuset exists.

Signed-off-by: Mel Gorman mgor...@techsingularity.net
Acked-by: David Rientjes rient...@google.com
Acked-by: Vlastimil Babka vba...@suse.cz
---
 include/linux/cpuset.h | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 1b357997cac5..6eb27cb480b7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
task_struct *p);
  */
 static inline unsigned int read_mems_allowed_begin(void)
 {
+   if (!cpusets_enabled())
+   return 0;
+
return read_seqcount_begin(current-mems_allowed_seq);
 }
 
@@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
  */
 static inline bool read_mems_allowed_retry(unsigned int seq)
 {
+   if (!cpusets_enabled())
+   return false;
+
return read_seqcount_retry(current-mems_allowed_seq, seq);
 }
 
-- 
2.4.6

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Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-07-28 Thread Vlastimil Babka 

On 07/20/2015 10:00 AM, Mel Gorman wrote:

From: Mel Gorman 

There is a seqcounter that protects spurious allocation fails when a task
is changing the allowed nodes in a cpuset. There is no need to check the
seqcounter until a cpuset exists.


If cpusets become enabled betwen _begin and _retry, then it will retry 
due to comparing with 0, but not crash, so it's safe.



Signed-off-by: Mel Gorman 


Acked-by: Vlastimil Babka 


---
  include/linux/cpuset.h | 6 ++
  1 file changed, 6 insertions(+)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 1b357997cac5..6eb27cb480b7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
task_struct *p);
   */
  static inline unsigned int read_mems_allowed_begin(void)
  {
+   if (!cpusets_enabled())
+   return 0;
+
return read_seqcount_begin(>mems_allowed_seq);
  }

@@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
   */
  static inline bool read_mems_allowed_retry(unsigned int seq)
  {
+   if (!cpusets_enabled())
+   return false;
+
return read_seqcount_retry(>mems_allowed_seq, seq);
  }




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Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-07-28 Thread Vlastimil Babka 

On 07/20/2015 10:00 AM, Mel Gorman wrote:

From: Mel Gorman mgor...@suse.de

There is a seqcounter that protects spurious allocation fails when a task
is changing the allowed nodes in a cpuset. There is no need to check the
seqcounter until a cpuset exists.


If cpusets become enabled betwen _begin and _retry, then it will retry 
due to comparing with 0, but not crash, so it's safe.



Signed-off-by: Mel Gorman mgor...@sujse.de


Acked-by: Vlastimil Babka vba...@suse.cz


---
  include/linux/cpuset.h | 6 ++
  1 file changed, 6 insertions(+)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 1b357997cac5..6eb27cb480b7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
task_struct *p);
   */
  static inline unsigned int read_mems_allowed_begin(void)
  {
+   if (!cpusets_enabled())
+   return 0;
+
return read_seqcount_begin(current-mems_allowed_seq);
  }

@@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
   */
  static inline bool read_mems_allowed_retry(unsigned int seq)
  {
+   if (!cpusets_enabled())
+   return false;
+
return read_seqcount_retry(current-mems_allowed_seq, seq);
  }




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Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-07-21 Thread David Rientjes 
On Mon, 20 Jul 2015, Mel Gorman wrote:

> From: Mel Gorman 
> 
> There is a seqcounter that protects spurious allocation fails when a task
> is changing the allowed nodes in a cpuset. There is no need to check the
> seqcounter until a cpuset exists.
> 
> Signed-off-by: Mel Gorman 

Acked-by: David Rientjes 

but there's a typo in your email address in the signed-off-by line.  Nice 
to know you actually type them by hand though :)
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Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-07-21 Thread David Rientjes 
On Mon, 20 Jul 2015, Mel Gorman wrote:

 From: Mel Gorman mgor...@suse.de
 
 There is a seqcounter that protects spurious allocation fails when a task
 is changing the allowed nodes in a cpuset. There is no need to check the
 seqcounter until a cpuset exists.
 
 Signed-off-by: Mel Gorman mgor...@sujse.de

Acked-by: David Rientjes rient...@google.com

but there's a typo in your email address in the signed-off-by line.  Nice 
to know you actually type them by hand though :)
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[PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-07-20 Thread Mel Gorman 
From: Mel Gorman 

There is a seqcounter that protects spurious allocation fails when a task
is changing the allowed nodes in a cpuset. There is no need to check the
seqcounter until a cpuset exists.

Signed-off-by: Mel Gorman 
---
 include/linux/cpuset.h | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 1b357997cac5..6eb27cb480b7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
task_struct *p);
  */
 static inline unsigned int read_mems_allowed_begin(void)
 {
+   if (!cpusets_enabled())
+   return 0;
+
return read_seqcount_begin(>mems_allowed_seq);
 }
 
@@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
  */
 static inline bool read_mems_allowed_retry(unsigned int seq)
 {
+   if (!cpusets_enabled())
+   return false;
+
return read_seqcount_retry(>mems_allowed_seq, seq);
 }
 
-- 
2.4.3

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[PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

2015-07-20 Thread Mel Gorman 
From: Mel Gorman mgor...@suse.de

There is a seqcounter that protects spurious allocation fails when a task
is changing the allowed nodes in a cpuset. There is no need to check the
seqcounter until a cpuset exists.

Signed-off-by: Mel Gorman mgor...@sujse.de
---
 include/linux/cpuset.h | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 1b357997cac5..6eb27cb480b7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct 
task_struct *p);
  */
 static inline unsigned int read_mems_allowed_begin(void)
 {
+   if (!cpusets_enabled())
+   return 0;
+
return read_seqcount_begin(current-mems_allowed_seq);
 }
 
@@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
  */
 static inline bool read_mems_allowed_retry(unsigned int seq)
 {
+   if (!cpusets_enabled())
+   return false;
+
return read_seqcount_retry(current-mems_allowed_seq, seq);
 }
 
-- 
2.4.3

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