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

[Pan Xinhui]

From: Pan Xinhui <xinhuix.pan@xxxxxxxxx>

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@xxxxxxxxx>
---
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
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