[PATCH 0/5] mm: modest useability enhancements for node sysfs attrs

[PATCH 0/5] mm: modest useability enhancements for node sysfs attrs

[Alex Chiang]

I've been poking at memory/node hotplug lately, and found myself wondering
what node a memory section or CPU might belong to.

Yes, the information is there in sysfs, but to me, having a symlink pointing
back to the node is so much more convenient.

Thanks,
/ac

---

Alex Chiang (5):
      mm: add numa node symlink for memory section in sysfs
      mm: refactor register_cpu_under_node()
      mm: refactor unregister_cpu_under_node()
      mm: add numa node symlink for cpu devices in sysfs
      Documentation: ABI: document /sys/devices/system/cpu/


 Documentation/ABI/testing/sysfs-devices-cpu    |   42 ++++++++++++++++++
 Documentation/ABI/testing/sysfs-devices-memory |   14 ++++++
 Documentation/memory-hotplug.txt               |   11 +++--
 drivers/base/node.c                            |   56 +++++++++++++++++-------
 4 files changed, 102 insertions(+), 21 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-devices-cpu

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[PATCH 1/5] mm: add numa node symlink for memory section in sysfs

[Alex Chiang]

Commit c04fc586c (mm: show node to memory section relationship with
symlinks in sysfs) created symlinks from nodes to memory sections, e.g.

/sys/devices/system/node/node1/memory135 -> ../../memory/memory135

If you're examining the memory section though and are wondering what
node it might belong to, you can find it by grovelling around in
sysfs, but it's a little cumbersome.

Add a reverse symlink for each memory section that points back to the
node to which it belongs.

Cc: Gary Hade <garyhade@us.ibm.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Alex Chiang <achiang@hp.com>
---

 Documentation/ABI/testing/sysfs-devices-memory |   14 +++++++++++++-
 Documentation/memory-hotplug.txt               |   11 +++++++----
 drivers/base/node.c                            |   11 ++++++++++-
 3 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory
index 9fe91c0..bf1627b 100644
--- a/Documentation/ABI/testing/sysfs-devices-memory
+++ b/Documentation/ABI/testing/sysfs-devices-memory
@@ -60,6 +60,19 @@ Description:
 Users:		hotplug memory remove tools
 		https://w3.opensource.ibm.com/projects/powerpc-utils/
 
+
+What:		/sys/devices/system/memoryX/nodeY
+Date:		October 2009
+Contact:	Linux Memory Management list <linux-mm@kvack.org>
+Description:
+		When CONFIG_NUMA is enabled, a symbolic link that
+		points to the corresponding NUMA node directory.
+
+		For example, the following symbolic link is created for
+		memory section 9 on node0:
+		/sys/devices/system/memory/memory9/node0 -> ../../node/node0
+
+
 What:		/sys/devices/system/node/nodeX/memoryY
 Date:		September 2008
 Contact:	Gary Hade <garyhade@us.ibm.com>
@@ -70,4 +83,3 @@ Description:
 		memory section directory.  For example, the following symbolic
 		link is created for memory section 9 on node0.
 		/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
-
diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
index bbc8a6a..57e7e9c 100644
--- a/Documentation/memory-hotplug.txt
+++ b/Documentation/memory-hotplug.txt
@@ -160,12 +160,15 @@ Under each section, you can see 4 files.
 NOTE:
   These directories/files appear after physical memory hotplug phase.
 
-If CONFIG_NUMA is enabled the
-/sys/devices/system/memory/memoryXXX memory section
-directories can also be accessed via symbolic links located in
-the /sys/devices/system/node/node* directories.  For example:
+If CONFIG_NUMA is enabled the memoryXXX/ directories can also be accessed
+via symbolic links located in the /sys/devices/system/node/node* directories.
+
+For example:
 /sys/devices/system/node/node0/memory9 -> ../../memory/memory9
 
+A backlink will also be created:
+/sys/devices/system/memory/memory9/node0 -> ../../node/node0
+
 --------------------------------
 4. Physical memory hot-add phase
 --------------------------------
diff --git a/drivers/base/node.c b/drivers/base/node.c
index 1fe5536..3108b21 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -268,6 +268,7 @@ static int get_nid_for_pfn(unsigned long pfn)
 /* register memory section under specified node if it spans that node */
 int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
 {
+	int ret;
 	unsigned long pfn, sect_start_pfn, sect_end_pfn;
 
 	if (!mem_blk)
@@ -284,9 +285,15 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
 			continue;
 		if (page_nid != nid)
 			continue;
-		return sysfs_create_link_nowarn(&node_devices[nid].sysdev.kobj,
+		ret = sysfs_create_link_nowarn(&node_devices[nid].sysdev.kobj,
 					&mem_blk->sysdev.kobj,
 					kobject_name(&mem_blk->sysdev.kobj));
+		if (ret)
+			return ret;
+
+		return sysfs_create_link_nowarn(&mem_blk->sysdev.kobj,
+				&node_devices[nid].sysdev.kobj,
+				kobject_name(&node_devices[nid].sysdev.kobj));
 	}
 	/* mem section does not span the specified node */
 	return 0;
@@ -315,6 +322,8 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk)
 			continue;
 		sysfs_remove_link(&node_devices[nid].sysdev.kobj,
 			 kobject_name(&mem_blk->sysdev.kobj));
+		sysfs_remove_link(&mem_blk->sysdev.kobj,
+			 kobject_name(&node_devices[nid].sysdev.kobj));
 	}
 	return 0;
 }

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Re: [PATCH 1/5] mm: add numa node symlink for memory section in sysfs

[KAMEZAWA Hiroyuki]

Alex Chiang wrote:
> Commit c04fc586c (mm: show node to memory section relationship with
> symlinks in sysfs) created symlinks from nodes to memory sections, e.g.
>
> /sys/devices/system/node/node1/memory135 -> ../../memory/memory135
>
> If you're examining the memory section though and are wondering what
> node it might belong to, you can find it by grovelling around in
> sysfs, but it's a little cumbersome.
>
> Add a reverse symlink for each memory section that points back to the
> node to which it belongs.
>
> Cc: Gary Hade <garyhade@us.ibm.com>
> Cc: Badari Pulavarty <pbadari@us.ibm.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Signed-off-by: Alex Chiang <achiang@hp.com>

2 yeas ago, I wanted to add this symlink. But don't...because
some vendor's host has no 1-to-1 relationship between a memsection
and a node. (I don't remember precisely, sorry....s390?)

Then, a memsection can be under prural nodes.

At brief look, this patch provides 1-to-1 relationship between them.
If it's ok for all stake-holders, I welcome this.

Thanks,
-Kame

> ---
>
>  Documentation/ABI/testing/sysfs-devices-memory |   14 +++++++++++++-
>  Documentation/memory-hotplug.txt               |   11 +++++++----
>  drivers/base/node.c                            |   11 ++++++++++-
>  3 files changed, 30 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-devices-memory
> b/Documentation/ABI/testing/sysfs-devices-memory
> index 9fe91c0..bf1627b 100644
> --- a/Documentation/ABI/testing/sysfs-devices-memory
> +++ b/Documentation/ABI/testing/sysfs-devices-memory
> @@ -60,6 +60,19 @@ Description:
>  Users:		hotplug memory remove tools
>  		https://w3.opensource.ibm.com/projects/powerpc-utils/
>
> +
> +What:		/sys/devices/system/memoryX/nodeY
> +Date:		October 2009
> +Contact:	Linux Memory Management list <linux-mm@kvack.org>
> +Description:
> +		When CONFIG_NUMA is enabled, a symbolic link that
> +		points to the corresponding NUMA node directory.
> +
> +		For example, the following symbolic link is created for
> +		memory section 9 on node0:
> +		/sys/devices/system/memory/memory9/node0 -> ../../node/node0
> +
> +
>  What:		/sys/devices/system/node/nodeX/memoryY
>  Date:		September 2008
>  Contact:	Gary Hade <garyhade@us.ibm.com>
> @@ -70,4 +83,3 @@ Description:
>  		memory section directory.  For example, the following symbolic
>  		link is created for memory section 9 on node0.
>  		/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
> -
> diff --git a/Documentation/memory-hotplug.txt
> b/Documentation/memory-hotplug.txt
> index bbc8a6a..57e7e9c 100644
> --- a/Documentation/memory-hotplug.txt
> +++ b/Documentation/memory-hotplug.txt
> @@ -160,12 +160,15 @@ Under each section, you can see 4 files.
>  NOTE:
>    These directories/files appear after physical memory hotplug phase.
>
> -If CONFIG_NUMA is enabled the
> -/sys/devices/system/memory/memoryXXX memory section
> -directories can also be accessed via symbolic links located in
> -the /sys/devices/system/node/node* directories.  For example:
> +If CONFIG_NUMA is enabled the memoryXXX/ directories can also be accessed
> +via symbolic links located in the /sys/devices/system/node/node*
> directories.
> +
> +For example:
>  /sys/devices/system/node/node0/memory9 -> ../../memory/memory9
>
> +A backlink will also be created:
> +/sys/devices/system/memory/memory9/node0 -> ../../node/node0
> +
>  --------------------------------
>  4. Physical memory hot-add phase
>  --------------------------------
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 1fe5536..3108b21 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -268,6 +268,7 @@ static int get_nid_for_pfn(unsigned long pfn)
>  /* register memory section under specified node if it spans that node */
>  int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
>  {
> +	int ret;
>  	unsigned long pfn, sect_start_pfn, sect_end_pfn;
>
>  	if (!mem_blk)
> @@ -284,9 +285,15 @@ int register_mem_sect_under_node(struct memory_block
> *mem_blk, int nid)
>  			continue;
>  		if (page_nid != nid)
>  			continue;
> -		return sysfs_create_link_nowarn(&node_devices[nid].sysdev.kobj,
> +		ret = sysfs_create_link_nowarn(&node_devices[nid].sysdev.kobj,
>  					&mem_blk->sysdev.kobj,
>  					kobject_name(&mem_blk->sysdev.kobj));
> +		if (ret)
> +			return ret;
> +
> +		return sysfs_create_link_nowarn(&mem_blk->sysdev.kobj,
> +				&node_devices[nid].sysdev.kobj,
> +				kobject_name(&node_devices[nid].sysdev.kobj));
>  	}
>  	/* mem section does not span the specified node */
>  	return 0;
> @@ -315,6 +322,8 @@ int unregister_mem_sect_under_nodes(struct
> memory_block *mem_blk)
>  			continue;
>  		sysfs_remove_link(&node_devices[nid].sysdev.kobj,
>  			 kobject_name(&mem_blk->sysdev.kobj));
> +		sysfs_remove_link(&mem_blk->sysdev.kobj,
> +			 kobject_name(&node_devices[nid].sysdev.kobj));
>  	}
>  	return 0;
>  }
>
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Re: [PATCH 1/5] mm: add numa node symlink for memory section in sysfs

[Alex Chiang]

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>:
> Alex Chiang wrote:
> > Commit c04fc586c (mm: show node to memory section relationship with
> > symlinks in sysfs) created symlinks from nodes to memory sections, e.g.
> >
> > /sys/devices/system/node/node1/memory135 -> ../../memory/memory135
> >
> > If you're examining the memory section though and are wondering what
> > node it might belong to, you can find it by grovelling around in
> > sysfs, but it's a little cumbersome.
> >
> > Add a reverse symlink for each memory section that points back to the
> > node to which it belongs.
> >
> > Cc: Gary Hade <garyhade@us.ibm.com>
> > Cc: Badari Pulavarty <pbadari@us.ibm.com>
> > Cc: Ingo Molnar <mingo@elte.hu>
> > Signed-off-by: Alex Chiang <achiang@hp.com>
> 
> 2 yeas ago, I wanted to add this symlink. But don't...because
> some vendor's host has no 1-to-1 relationship between a memsection
> and a node. (I don't remember precisely, sorry....s390?)

Hm, ok. I'll cc the s390 folks in the next version of this series.

Thanks for the pointer.

/ac

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[PATCH 2/5] mm: refactor register_cpu_under_node()

[Alex Chiang]

By returning early if the node is not online, we can unindent the
interesting code by one level.

No functional change.

Signed-off-by: Alex Chiang <achiang@hp.com>
---

 drivers/base/node.c |   20 +++++++++++---------
 1 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 3108b21..ef7dd22 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -227,16 +227,18 @@ struct node node_devices[MAX_NUMNODES];
  */
 int register_cpu_under_node(unsigned int cpu, unsigned int nid)
 {
-	if (node_online(nid)) {
-		struct sys_device *obj = get_cpu_sysdev(cpu);
-		if (!obj)
-			return 0;
-		return sysfs_create_link(&node_devices[nid].sysdev.kobj,
-					 &obj->kobj,
-					 kobject_name(&obj->kobj));
-	 }
+	struct sys_device *obj;
 
-	return 0;
+	if (!node_online(nid))
+		return 0;
+
+	obj = get_cpu_sysdev(cpu);
+	if (!obj)
+		return 0;
+
+	return sysfs_create_link(&node_devices[nid].sysdev.kobj,
+				&obj->kobj,
+				kobject_name(&obj->kobj));
 }
 
 int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)

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[PATCH 3/5] mm: refactor unregister_cpu_under_node()

[Alex Chiang]

By returning early if the node is not online, we can unindent the
interesting code by two levels.

No functional change.

Signed-off-by: Alex Chiang <achiang@hp.com>
---

 drivers/base/node.c |   18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index ef7dd22..ffda067 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -243,12 +243,18 @@ int register_cpu_under_node(unsigned int cpu, unsigned int nid)
 
 int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
 {
-	if (node_online(nid)) {
-		struct sys_device *obj = get_cpu_sysdev(cpu);
-		if (obj)
-			sysfs_remove_link(&node_devices[nid].sysdev.kobj,
-					 kobject_name(&obj->kobj));
-	}
+	struct sys_device *obj;
+
+	if (!node_online(nid))
+		return 0;
+
+	obj = get_cpu_sysdev(cpu);
+	if (!obj)
+		return 0;
+
+	sysfs_remove_link(&node_devices[nid].sysdev.kobj,
+			  kobject_name(&obj->kobj));
+
 	return 0;
 }
 

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[PATCH 4/5] mm: add numa node symlink for cpu devices in sysfs

[Alex Chiang]

You can discover which CPUs belong to a NUMA node by examining
/sys/devices/system/node/$node/

However, it's not convenient to go in the other direction, when looking at
/sys/devices/system/cpu/$cpu/

Yes, you can muck about in sysfs, but adding these symlinks makes
life a lot more convenient.

Signed-off-by: Alex Chiang <achiang@hp.com>
---

 drivers/base/node.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index ffda067..47a4997 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -227,6 +227,7 @@ struct node node_devices[MAX_NUMNODES];
  */
 int register_cpu_under_node(unsigned int cpu, unsigned int nid)
 {
+	int ret;
 	struct sys_device *obj;
 
 	if (!node_online(nid))
@@ -236,9 +237,13 @@ int register_cpu_under_node(unsigned int cpu, unsigned int nid)
 	if (!obj)
 		return 0;
 
-	return sysfs_create_link(&node_devices[nid].sysdev.kobj,
+	ret = sysfs_create_link(&node_devices[nid].sysdev.kobj,
 				&obj->kobj,
 				kobject_name(&obj->kobj));
+
+	return sysfs_create_link(&obj->kobj,
+				 &node_devices[nid].sysdev.kobj,
+				 kobject_name(&node_devices[nid].sysdev.kobj));
 }
 
 int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
@@ -254,6 +259,8 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
 
 	sysfs_remove_link(&node_devices[nid].sysdev.kobj,
 			  kobject_name(&obj->kobj));
+	sysfs_remove_link(&obj->kobj,
+			  kobject_name(&node_devices[nid].sysdev.kobj));
 
 	return 0;
 }

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Re: [PATCH 4/5] mm: add numa node symlink for cpu devices in sysfs

[David Rientjes]

On Mon, 19 Oct 2009, Alex Chiang wrote:

> You can discover which CPUs belong to a NUMA node by examining
> /sys/devices/system/node/$node/
> 

You mean /sys/devices/system/node/node# ?

> However, it's not convenient to go in the other direction, when looking at
> /sys/devices/system/cpu/$cpu/
> 

.../cpu/cpu# ?

> Yes, you can muck about in sysfs, but adding these symlinks makes
> life a lot more convenient.
> 
> Signed-off-by: Alex Chiang <achiang@hp.com>
> ---
> 
>  drivers/base/node.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index ffda067..47a4997 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -227,6 +227,7 @@ struct node node_devices[MAX_NUMNODES];
>   */
>  int register_cpu_under_node(unsigned int cpu, unsigned int nid)
>  {
> +	int ret;
>  	struct sys_device *obj;
>  
>  	if (!node_online(nid))
> @@ -236,9 +237,13 @@ int register_cpu_under_node(unsigned int cpu, unsigned int nid)
>  	if (!obj)
>  		return 0;
>  
> -	return sysfs_create_link(&node_devices[nid].sysdev.kobj,
> +	ret = sysfs_create_link(&node_devices[nid].sysdev.kobj,
>  				&obj->kobj,
>  				kobject_name(&obj->kobj));
> +
> +	return sysfs_create_link(&obj->kobj,
> +				 &node_devices[nid].sysdev.kobj,
> +				 kobject_name(&node_devices[nid].sysdev.kobj));
>  }
>  
>  int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)

That can't be right, you're ignoring the return value of the first 
sysfs_create_link().

The return values of register_cpu_under_node() and 
unregister_cpu_under_node() are always ignored, so it would probably be 
best to convert these to be void functions.  That doesn't mean you can 
simply ignore the result of the first sysfs_create_link(), though: the 
second should probably be suppressed if the first returns an error.

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Re: [PATCH 4/5] mm: add numa node symlink for cpu devices in sysfs

[Alex Chiang]

* David Rientjes <rientjes@google.com>:
> On Mon, 19 Oct 2009, Alex Chiang wrote:
> 
> > You can discover which CPUs belong to a NUMA node by examining
> > /sys/devices/system/node/$node/
> > 
> 
> You mean /sys/devices/system/node/node# ?

Hm, in PCI land, I've been using $foo to indicate a variable in
documentation I've written, but I can certainly use foo# if
that's the preferred style.

> > However, it's not convenient to go in the other direction, when looking at
> > /sys/devices/system/cpu/$cpu/
> > 
> 
> .../cpu/cpu# ?
> 
> > Yes, you can muck about in sysfs, but adding these symlinks makes
> > life a lot more convenient.
> > 
> > Signed-off-by: Alex Chiang <achiang@hp.com>
> > ---
> > 
> >  drivers/base/node.c |    9 ++++++++-
> >  1 files changed, 8 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/base/node.c b/drivers/base/node.c
> > index ffda067..47a4997 100644
> > --- a/drivers/base/node.c
> > +++ b/drivers/base/node.c
> > @@ -227,6 +227,7 @@ struct node node_devices[MAX_NUMNODES];
> >   */
> >  int register_cpu_under_node(unsigned int cpu, unsigned int nid)
> >  {
> > +	int ret;
> >  	struct sys_device *obj;
> >  
> >  	if (!node_online(nid))
> > @@ -236,9 +237,13 @@ int register_cpu_under_node(unsigned int cpu, unsigned int nid)
> >  	if (!obj)
> >  		return 0;
> >  
> > -	return sysfs_create_link(&node_devices[nid].sysdev.kobj,
> > +	ret = sysfs_create_link(&node_devices[nid].sysdev.kobj,
> >  				&obj->kobj,
> >  				kobject_name(&obj->kobj));
> > +
> > +	return sysfs_create_link(&obj->kobj,
> > +				 &node_devices[nid].sysdev.kobj,
> > +				 kobject_name(&node_devices[nid].sysdev.kobj));
> >  }
> >  
> >  int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
> 
> That can't be right, you're ignoring the return value of the first 
> sysfs_create_link().

This was a simple oversight. my intent was to return early if the
first call to sysfs_create_link() failed.

> The return values of register_cpu_under_node() and 
> unregister_cpu_under_node() are always ignored, so it would probably be 
> best to convert these to be void functions.  That doesn't mean you can 
> simply ignore the result of the first sysfs_create_link(), though: the 
> second should probably be suppressed if the first returns an error.
> 

I didn't want to change too much in the patch. Changing the
function signature seems a bit overeager, but if you have strong
feelings, I can do so.

Thanks for the review.

/ac

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Re: [PATCH 4/5] mm: add numa node symlink for cpu devices in sysfs

[David Rientjes]

On Tue, 20 Oct 2009, Alex Chiang wrote:

> * David Rientjes <rientjes@google.com>:
> > On Mon, 19 Oct 2009, Alex Chiang wrote:
> > 
> > > You can discover which CPUs belong to a NUMA node by examining
> > > /sys/devices/system/node/$node/
> > > 
> > 
> > You mean /sys/devices/system/node/node# ?
> 
> Hm, in PCI land, I've been using $foo to indicate a variable in
> documentation I've written, but I can certainly use foo# if
> that's the preferred style.
> 

I'm referring to the directories in /sys/devices/system/node/ being 
'node13' for example, and not '13' as your changelog indicates.

> > > However, it's not convenient to go in the other direction, when looking at
> > > /sys/devices/system/cpu/$cpu/
> > > 
> > 
> > .../cpu/cpu# ?
> > 

Same here.

> > The return values of register_cpu_under_node() and 
> > unregister_cpu_under_node() are always ignored, so it would probably be 
> > best to convert these to be void functions.  That doesn't mean you can 
> > simply ignore the result of the first sysfs_create_link(), though: the 
> > second should probably be suppressed if the first returns an error.
> > 
> 
> I didn't want to change too much in the patch. Changing the
> function signature seems a bit overeager, but if you have strong
> feelings, I can do so.
> 

It's entirely up to you if you want to change them to be void.  I thought 
it would be cleaner if the first patch in the series would convert them to 
void on the basis that the return value is never actually used and then 
the following patches simply return on error conditions.

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Re: [PATCH 4/5] mm: add numa node symlink for cpu devices in sysfs

[Alex Chiang]

* David Rientjes <rientjes@google.com>:
> On Tue, 20 Oct 2009, Alex Chiang wrote:
> > * David Rientjes <rientjes@google.com>:
> > > The return values of register_cpu_under_node() and 
> > > unregister_cpu_under_node() are always ignored, so it would probably be 
> > > best to convert these to be void functions.  That doesn't mean you can 
> > > simply ignore the result of the first sysfs_create_link(), though: the 
> > > second should probably be suppressed if the first returns an error.
> > 
> > I didn't want to change too much in the patch. Changing the
> > function signature seems a bit overeager, but if you have strong
> > feelings, I can do so.
> 
> It's entirely up to you if you want to change them to be void.  I thought 
> it would be cleaner if the first patch in the series would convert them to 
> void on the basis that the return value is never actually used and then 
> the following patches simply return on error conditions.

I made the conversion as you suggested, but discovered under
sparse that:

	drivers/base/node.c: In function a??register_cpu_under_nodea??:
	drivers/base/node.c:245: warning: ignoring return value of
	a??sysfs_create_linka??, declared with attribute warn_unused_result

I wasn't very happy with the result after doing something with
the return value of sysfs_create_link to make sparse shutup.
Seemed unnatural and very much had the feeling of jumping through
hoops just to make an automated tool be quiet.

So, I'll just leave [un]register_cpu_under_node() as returning
int. It not only makes the patch feel better, but if we do ever
want to decide to unroll due to an error in sysfs_create_link,
we'll have the information available at the callsites.

Thanks.
/ac

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[PATCH 5/5] Documentation: ABI: document /sys/devices/system/cpu/

[Alex Chiang]

This interface has been around for a long time, but hasn't been
officially documented.

Since I wanted to extend the ABI, I figured I would document what
already existed.

Cc: Greg KH <greg@kroah.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Alex Chiang <achiang@hp.com>
---

 Documentation/ABI/testing/sysfs-devices-cpu |   42 +++++++++++++++++++++++++++
 1 files changed, 42 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-devices-cpu

diff --git a/Documentation/ABI/testing/sysfs-devices-cpu b/Documentation/ABI/testing/sysfs-devices-cpu
new file mode 100644
index 0000000..9070889
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-cpu
@@ -0,0 +1,42 @@
+What:		/sys/devices/system/cpu/
+Date:		October 2009
+Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description:
+		A collection of CPU attributes, including cache information,
+		topology, and frequency. It also contains a mechanism to
+		logically hotplug CPUs.
+
+		The actual attributes present are architecture and
+		configuration dependent.
+
+
+What:		/sys/devices/system/cpu/$cpu/online
+Date:		January 2006
+Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description:
+		When CONFIG_HOTPLUG_CPU is enabled, allows the user to
+		discover and change the online state of a CPU. To discover
+		the state:
+
+		cat /sys/devices/system/cpu/$cpu/online
+
+		A value of 0 indicates the CPU is offline. A value of 1
+		indicates it is online. To change the state, echo the
+		desired new state into the file:
+
+		echo [0|1] > /sys/devices/system/cpu/$cpu/online
+
+		For more information, please read Documentation/cpu-hotplug.txt
+
+
+What:		/sys/devices/system/cpu/$cpu/node
+Date:		October 2009
+Contact:	Linux memory management mailing list <linux-mm@kvack.org>
+Description:
+		When CONFIG_NUMA is enabled, a symbolic link that points
+		to the corresponding NUMA node directory.
+
+		For example, the following symlink is created for cpu42
+		in NUMA node 2:
+
+		/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2

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Re: [PATCH 5/5] Documentation: ABI: document /sys/devices/system/cpu/

[David Rientjes]

On Mon, 19 Oct 2009, Alex Chiang wrote:

> diff --git a/Documentation/ABI/testing/sysfs-devices-cpu b/Documentation/ABI/testing/sysfs-devices-cpu
> new file mode 100644
> index 0000000..9070889
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-devices-cpu

Shouldn't this be called sysfs-devices-system-cpu?

I see what you're doing: /sys/devices/system/node/* files are contained in 
sysfs-devices-memory, but I think it would be helpful to have a more 
strict naming scheme so that the contents of a sysfs directory are 
described by a file of the same name.

> @@ -0,0 +1,42 @@
> +What:		/sys/devices/system/cpu/
> +Date:		October 2009
> +Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> +Description:
> +		A collection of CPU attributes, including cache information,
> +		topology, and frequency. It also contains a mechanism to
> +		logically hotplug CPUs.
> +
> +		The actual attributes present are architecture and
> +		configuration dependent.
> +
> +
> +What:		/sys/devices/system/cpu/$cpu/online

cpu# ?

> +Date:		January 2006
> +Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> +Description:
> +		When CONFIG_HOTPLUG_CPU is enabled, allows the user to
> +		discover and change the online state of a CPU. To discover
> +		the state:

This is present even without CONFIG_HOTPLUG_CPU.

> +
> +		cat /sys/devices/system/cpu/$cpu/online
> +
> +		A value of 0 indicates the CPU is offline. A value of 1
> +		indicates it is online. To change the state, echo the
> +		desired new state into the file:
> +
> +		echo [0|1] > /sys/devices/system/cpu/$cpu/online
> +
> +		For more information, please read Documentation/cpu-hotplug.txt
> +
> +
> +What:		/sys/devices/system/cpu/$cpu/node
> +Date:		October 2009
> +Contact:	Linux memory management mailing list <linux-mm@kvack.org>
> +Description:
> +		When CONFIG_NUMA is enabled, a symbolic link that points
> +		to the corresponding NUMA node directory.
> +
> +		For example, the following symlink is created for cpu42
> +		in NUMA node 2:
> +
> +		/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
> 


Would it be possible for you to document all entities in 
/sys/devices/system/cpu/* in this new file (requiring a folding of 
Documentation/ABI/testing/sysfs-devices-cache_disable into it)?

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Re: [PATCH 5/5] Documentation: ABI: document /sys/devices/system/cpu/

[Alex Chiang]

* David Rientjes <rientjes@google.com>:
> On Mon, 19 Oct 2009, Alex Chiang wrote:
> 
> > diff --git a/Documentation/ABI/testing/sysfs-devices-cpu b/Documentation/ABI/testing/sysfs-devices-cpu
> > new file mode 100644
> > index 0000000..9070889
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-devices-cpu
> 
> Shouldn't this be called sysfs-devices-system-cpu?
> 
> I see what you're doing: /sys/devices/system/node/* files are contained in 
> sysfs-devices-memory, but I think it would be helpful to have a more 
> strict naming scheme so that the contents of a sysfs directory are 
> described by a file of the same name.

Yeah, I was just trying to follow an earlier example. But you're
right, since I'm creating a brand new file, I can do it the Right
Way (tm).

> > @@ -0,0 +1,42 @@
> > +What:		/sys/devices/system/cpu/
> > +Date:		October 2009
> > +Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> > +Description:
> > +		A collection of CPU attributes, including cache information,
> > +		topology, and frequency. It also contains a mechanism to
> > +		logically hotplug CPUs.
> > +
> > +		The actual attributes present are architecture and
> > +		configuration dependent.
> > +
> > +
> > +What:		/sys/devices/system/cpu/$cpu/online
> 
> cpu# ?

Sure, will change (depending on response to my earlier email).

> > +Date:		January 2006
> > +Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> > +Description:
> > +		When CONFIG_HOTPLUG_CPU is enabled, allows the user to
> > +		discover and change the online state of a CPU. To discover
> > +		the state:
> 
> This is present even without CONFIG_HOTPLUG_CPU.

That's what I get for not checking. Thank you for correcting me.

> > +
> > +		cat /sys/devices/system/cpu/$cpu/online
> > +
> > +		A value of 0 indicates the CPU is offline. A value of 1
> > +		indicates it is online. To change the state, echo the
> > +		desired new state into the file:
> > +
> > +		echo [0|1] > /sys/devices/system/cpu/$cpu/online
> > +
> > +		For more information, please read Documentation/cpu-hotplug.txt
> > +
> > +
> > +What:		/sys/devices/system/cpu/$cpu/node
> > +Date:		October 2009
> > +Contact:	Linux memory management mailing list <linux-mm@kvack.org>
> > +Description:
> > +		When CONFIG_NUMA is enabled, a symbolic link that points
> > +		to the corresponding NUMA node directory.
> > +
> > +		For example, the following symlink is created for cpu42
> > +		in NUMA node 2:
> > +
> > +		/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
> > 
> 
> 
> Would it be possible for you to document all entities in 
> /sys/devices/system/cpu/* in this new file (requiring a folding of 
> Documentation/ABI/testing/sysfs-devices-cache_disable into it)?
 
I'll give it a go. There are quite a few things in that directory
though, like topology information, frequency, etc. that I wasn't
so excited about documenting.

But if that's the tax to create my new symlinks, I'll pay it. ;)

Thanks for the review,
/ac

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Re: [PATCH 5/5] Documentation: ABI: document /sys/devices/system/cpu/

[David Rientjes]

On Tue, 20 Oct 2009, Alex Chiang wrote:

> > Would it be possible for you to document all entities in 
> > /sys/devices/system/cpu/* in this new file (requiring a folding of 
> > Documentation/ABI/testing/sysfs-devices-cache_disable into it)?
>  
> I'll give it a go. There are quite a few things in that directory
> though, like topology information, frequency, etc. that I wasn't
> so excited about documenting.
> 

Those are usually the ones where documentation is the most valuable and 
I'm sure would be greatly appreciated.

> But if that's the tax to create my new symlinks, I'll pay it. ;)
> 

It's definitely not required, I just thought it was a good opportunity to 
document all the contents under /sys/devices/system/cpu if you're going to 
do some of them.  It's up to you.

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