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

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Message-ID: <55B0B9BB.50800@intel.com>
Date:	Thu, 23 Jul 2015 17:54:03 +0800
From:	Pan Xinhui <xinhuix.pan@...el.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, bp@...e.de, toshi.kani@...com,
	jgross@...e.com, mcgrof@...e.com,
	"mnipxh@....com" <mnipxh@....com>,
	"yanmin_zhang@...ux.intel.com" <yanmin_zhang@...ux.intel.com>
Subject: [PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype
  list

From: Pan Xinhui <xinhuix.pan@...el.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@...el.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
--
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