[PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype list

[PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype list

[Pan Xinhui]

From: Pan Xinhui <xinhuix.pan@intel.com>

There are many nodes in the PAT memtype rb-tree. When we dump this tree
we call kzalloc every time to copy nodes. Actually these kzalloc are not
necessary. Lets do a optimization now.

Let seq_file core create an *entry* when open and free it when release.
*entry* is stored as seq->private, so we can use it in seq_operations
callback who traverse/output the PAT memtype rb-tree only. Lots of
unnecessary kzalloc could be avoided now.

Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
---
v1 -> v2:
	Use seq_open/release_private. let seq_file core handle memory alloc/free.
	seq_operations callbacks now only traverse/output the PAT rb-tree.
---
 arch/x86/mm/pat.c | 28 ++++++++++------------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 268b2c8..53920be 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -1001,41 +1001,33 @@ EXPORT_SYMBOL_GPL(pgprot_writethrough);
 
 #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_PAT)
 
-static struct memtype *memtype_get_idx(loff_t pos)
+static struct memtype *memtype_get_idx(struct memtype *entry, loff_t pos)
 {
-	struct memtype *print_entry;
 	int ret;
 
-	print_entry  = kzalloc(sizeof(struct memtype), GFP_KERNEL);
-	if (!print_entry)
-		return NULL;
-
 	spin_lock(&memtype_lock);
-	ret = rbt_memtype_copy_nth_element(print_entry, pos);
+	ret = rbt_memtype_copy_nth_element(entry, pos);
 	spin_unlock(&memtype_lock);
 
-	if (!ret) {
-		return print_entry;
-	} else {
-		kfree(print_entry);
-		return NULL;
-	}
+	return ret ? NULL : entry;
 }
 
 static void *memtype_seq_start(struct seq_file *seq, loff_t *pos)
 {
+	struct memtype *entry = seq->private;
+
 	if (*pos == 0) {
 		++*pos;
 		seq_puts(seq, "PAT memtype list:\n");
 	}
 
-	return memtype_get_idx(*pos);
+	return memtype_get_idx(entry, *pos);
 }
 
 static void *memtype_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
 	++*pos;
-	return memtype_get_idx(*pos);
+	return memtype_get_idx((struct memtype *)v, *pos);
 }
 
 static void memtype_seq_stop(struct seq_file *seq, void *v)
@@ -1048,7 +1040,6 @@ static int memtype_seq_show(struct seq_file *seq, void *v)
 
 	seq_printf(seq, "%s @ 0x%Lx-0x%Lx\n", cattr_name(print_entry->type),
 			print_entry->start, print_entry->end);
-	kfree(print_entry);
 
 	return 0;
 }
@@ -1062,14 +1053,15 @@ static const struct seq_operations memtype_seq_ops = {
 
 static int memtype_seq_open(struct inode *inode, struct file *file)
 {
-	return seq_open(file, &memtype_seq_ops);
+	return seq_open_private(file, &memtype_seq_ops,
+							sizeof(struct memtype));
 }
 
 static const struct file_operations memtype_fops = {
 	.open    = memtype_seq_open,
 	.read    = seq_read,
 	.llseek  = seq_lseek,
-	.release = seq_release,
+	.release = seq_release_private,
 };
 
 static int __init pat_memtype_list_init(void)
-- 
1.9.1

[PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype list

[Pan Xinhui]

From: Pan Xinhui <xinhuix.pan@intel.com>

There are many nodes in the PAT memtype rb-tree. When we dump this tree
we call kzalloc every time to copy nodes. Actually these kzalloc are not
necessary. Lets do a optimization now.

Create an *entry* in memtype_seq_start(), and free it in
memtype_seq_stop(). These two callback functions are alwasys called in
pair. Also because memtype_seq_show() is usually used only for
outputing. Seems memtype_seq_show is not the best place to free the
*entry*

And reuse the *entry* in memtype_seq_next() to enhance the performance.

Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
---
 arch/x86/mm/pat.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 268b2c8..6302119 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -1001,45 +1001,42 @@ EXPORT_SYMBOL_GPL(pgprot_writethrough);
 
 #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_PAT)
 
-static struct memtype *memtype_get_idx(loff_t pos)
+static struct memtype *memtype_get_idx(struct memtype *entry, loff_t pos)
 {
-	struct memtype *print_entry;
 	int ret;
 
-	print_entry  = kzalloc(sizeof(struct memtype), GFP_KERNEL);
-	if (!print_entry)
-		return NULL;
-
 	spin_lock(&memtype_lock);
-	ret = rbt_memtype_copy_nth_element(print_entry, pos);
+	ret = rbt_memtype_copy_nth_element(entry, pos);
 	spin_unlock(&memtype_lock);
 
-	if (!ret) {
-		return print_entry;
-	} else {
-		kfree(print_entry);
-		return NULL;
-	}
+	return ret ? NULL : entry;
 }
 
 static void *memtype_seq_start(struct seq_file *seq, loff_t *pos)
 {
+	struct memtype *entry;
+
 	if (*pos == 0) {
 		++*pos;
 		seq_puts(seq, "PAT memtype list:\n");
 	}
 
-	return memtype_get_idx(*pos);
+	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+	seq->private = entry;
+	if (!entry)
+		return NULL;
+	return memtype_get_idx(entry, *pos);
 }
 
 static void *memtype_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
 	++*pos;
-	return memtype_get_idx(*pos);
+	return memtype_get_idx((struct memtype *)v, *pos);
 }
 
 static void memtype_seq_stop(struct seq_file *seq, void *v)
 {
+	kfree(seq->private);
 }
 
 static int memtype_seq_show(struct seq_file *seq, void *v)
@@ -1048,7 +1045,6 @@ static int memtype_seq_show(struct seq_file *seq, void *v)
 
 	seq_printf(seq, "%s @ 0x%Lx-0x%Lx\n", cattr_name(print_entry->type),
 			print_entry->start, print_entry->end);
-	kfree(print_entry);
 
 	return 0;
 }
-- 
1.9.1

RE: [PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype list

[Elliott, Robert (Server Storage)]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 1651 bytes --]

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> owner@vger.kernel.org] On Behalf Of Pan Xinhui
> Sent: Thursday, July 23, 2015 4:54 AM
> To: linux-kernel@vger.kernel.org
> Subject: [PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype
> list
...
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index 268b2c8..6302119 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -1001,45 +1001,42 @@ EXPORT_SYMBOL_GPL(pgprot_writethrough);
> 
>  #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_PAT)
> 
> -static struct memtype *memtype_get_idx(loff_t pos)
> +static struct memtype *memtype_get_idx(struct memtype *entry, loff_t pos)
>  {
> -	struct memtype *print_entry;
>  	int ret;
> 
> -	print_entry  = kzalloc(sizeof(struct memtype), GFP_KERNEL);
> -	if (!print_entry)
> -		return NULL;
> -
>  	spin_lock(&memtype_lock);
> -	ret = rbt_memtype_copy_nth_element(print_entry, pos);
> +	ret = rbt_memtype_copy_nth_element(entry, pos);
>  	spin_unlock(&memtype_lock);
> 
> -	if (!ret) {
> -		return print_entry;
> -	} else {
> -		kfree(print_entry);
> -		return NULL;
> -	}
> +	return ret ? NULL : entry;
>  }
> 
...
>  static void memtype_seq_stop(struct seq_file *seq, void *v)
>  {
> +	kfree(seq->private);
>  }
> 

Consider adding 
	seq->private = NULL; 
so the stale pointer isn't left around.  There's probably not
much risk of accessing it, but NULL is safer in case it is.

---
Robert Elliott, HP Server Storage
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Re: [PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype list

[Pan Xinhui]

hi, Elliott
	thanks for your reply. :)

On 2015年07月23日 22:53, Elliott, Robert (Server Storage) wrote:
>> -----Original Message-----
>> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
>> owner@vger.kernel.org] On Behalf Of Pan Xinhui
>> Sent: Thursday, July 23, 2015 4:54 AM
>> To: linux-kernel@vger.kernel.org
>> Subject: [PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype
>> list
> ...
>> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
>> index 268b2c8..6302119 100644
>> --- a/arch/x86/mm/pat.c
>> +++ b/arch/x86/mm/pat.c
>> @@ -1001,45 +1001,42 @@ EXPORT_SYMBOL_GPL(pgprot_writethrough);
>>
>>  #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_PAT)
>>
>> -static struct memtype *memtype_get_idx(loff_t pos)
>> +static struct memtype *memtype_get_idx(struct memtype *entry, loff_t pos)
>>  {
>> -     struct memtype *print_entry;
>>       int ret;
>>
>> -     print_entry  = kzalloc(sizeof(struct memtype), GFP_KERNEL);
>> -     if (!print_entry)
>> -             return NULL;
>> -
>>       spin_lock(&memtype_lock);
>> -     ret = rbt_memtype_copy_nth_element(print_entry, pos);
>> +     ret = rbt_memtype_copy_nth_element(entry, pos);
>>       spin_unlock(&memtype_lock);
>>
>> -     if (!ret) {
>> -             return print_entry;
>> -     } else {
>> -             kfree(print_entry);
>> -             return NULL;
>> -     }
>> +     return ret ? NULL : entry;
>>  }
>>
> ...
>>  static void memtype_seq_stop(struct seq_file *seq, void *v)
>>  {
>> +     kfree(seq->private);
>>  }
>>
> 
> Consider adding
>         seq->private = NULL;
> so the stale pointer isn't left around.  There's probably not
> much risk of accessing it, but NULL is safer in case it is.
> 
I know exactly what are you worrying about.
start and stop callback is still not the best place to alloc/free the *entry*. you are worrying about that some codes might touch it.

seq_file.c has offered seq_open_private and seq_release_private. we can make use of them. :)
I will work out patch v2, this time I will Cc you. I am very happy if you could review it at any free time. :)

thanks
xinhui
> ---
> Robert Elliott, HP Server Storage
>