linux-kernel - [PATCH] EXT2: Remove superblock lock contention in ext2

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Message-Id: <1158611794.11940.40.camel@kleikamp.austin.ibm.com>
Date:	Mon, 18 Sep 2006 15:36:33 -0500
From:	Dave Kleikamp <shaggy@...tin.ibm.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	Valerie Henson <val_henson@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: [PATCH] EXT2: Remove superblock lock contention in ext2_statfs

EXT2: Remove superblock lock contention in ext2_statfs

Fix a performance degradation introduced in 2.6.17.  (30% degradation running
dbench with 16 threads)

Patch 21730eed11de42f22afcbd43f450a1872a0b5ea1, which claims to make
EXT2_DEBUG work again, moves the taking of the kernel lock out of debug-only
code in ext2_count_free_inodes and ext2_count_free_blocks and into
ext2_statfs.  This patch reverses that part of the patch.

Signed-off-by: Dave Kleikamp <shaggy@...tin.ibm.com>

diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
index d487043..fddefff 100644
--- a/fs/ext2/balloc.c
+++ b/fs/ext2/balloc.c
@@ -539,7 +539,6 @@ unsigned long ext2_count_free (struct bu
 
 #endif  /*  EXT2FS_DEBUG  */
 
-/* Superblock must be locked */
 unsigned long ext2_count_free_blocks (struct super_block * sb)
 {
 	struct ext2_group_desc * desc;
@@ -549,6 +548,7 @@ #ifdef EXT2FS_DEBUG
 	unsigned long bitmap_count, x;
 	struct ext2_super_block *es;
 
+	lock_super(sb);
 	es = EXT2_SB(sb)->s_es;
 	desc_count = 0;
 	bitmap_count = 0;
@@ -572,6 +572,7 @@ #ifdef EXT2FS_DEBUG
 	printk("ext2_count_free_blocks: stored = %lu, computed = %lu, %lu\n",
 		(long)le32_to_cpu(es->s_free_blocks_count),
 		desc_count, bitmap_count);
+	unlock_super(sb);
 	return bitmap_count;
 #else
         for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c
index de85c61..5d1d1c9 100644
--- a/fs/ext2/ialloc.c
+++ b/fs/ext2/ialloc.c
@@ -637,7 +637,6 @@ fail:
 	return ERR_PTR(err);
 }
 
-/* Superblock must be locked */
 unsigned long ext2_count_free_inodes (struct super_block * sb)
 {
 	struct ext2_group_desc *desc;
@@ -649,6 +648,7 @@ #ifdef EXT2FS_DEBUG
 	unsigned long bitmap_count = 0;
 	struct buffer_head *bitmap_bh = NULL;
 
+	lock_super(sb);
 	es = EXT2_SB(sb)->s_es;
 	for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
 		unsigned x;
@@ -671,6 +671,7 @@ #ifdef EXT2FS_DEBUG
 	printk("ext2_count_free_inodes: stored = %lu, computed = %lu, %lu\n",
 		percpu_counter_read(&EXT2_SB(sb)->s_freeinodes_counter),
 		desc_count, bitmap_count);
+	unlock_super(sb);
 	return desc_count;
 #else
 	for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index ca5bfb6..4286ff6 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -1083,7 +1083,6 @@ static int ext2_statfs (struct dentry * 
 	unsigned long overhead;
 	int i;
 
-	lock_super(sb);
 	if (test_opt (sb, MINIX_DF))
 		overhead = 0;
 	else {
@@ -1124,7 +1123,6 @@ static int ext2_statfs (struct dentry * 
 	buf->f_files = le32_to_cpu(sbi->s_es->s_inodes_count);
 	buf->f_ffree = ext2_count_free_inodes (sb);
 	buf->f_namelen = EXT2_NAME_LEN;
-	unlock_super(sb);
 	return 0;
 }
 

-- 
David Kleikamp
IBM Linux Technology Center

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