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Date:	Thu, 12 Jul 2012 14:48:23 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	linux-ext4@...r.kernel.org
Cc:	Zach Brown <zab@...bo.net>, Andreas Dilger <adilger@...ger.ca>,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: [PATCH v2] ext4: dynamical adjust the length of zero-out chunk

From: Zheng Liu <wenqing.lz@...bao.com>

Currently in ext4 the length of zero-out chunk is set to 7.  But it is
too short so that it will cause a lot of fragmentation of extent when
we use fallocate to preallocate some uninitialized extents and the
workload frequently does some uninitialized extent conversions.  Thus,
now we set it to 256 (1MB chunk), and put it into super block in order
to adjust it dynamically in sysfs.

CC: Zach Brown <zab@...bo.net>
CC: Andreas Dilger <adilger@...ger.ca>
Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
---
v2 <- v1:
 * use a on-stack copy to avoid seeing differenet values
 * add missing spaces around '*'

 fs/ext4/ext4.h    |    3 +++
 fs/ext4/extents.c |   13 ++++++++-----
 fs/ext4/super.c   |    3 +++
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index cfc4e01..0f44577 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1265,6 +1265,9 @@ struct ext4_sb_info {
 	/* locality groups */
 	struct ext4_locality_group __percpu *s_locality_groups;
 
+	/* the size of zero-out chunk */
+	unsigned int s_extent_zeroout_len;
+
 	/* for write statistics */
 	unsigned long s_sectors_written_start;
 	u64 s_kbytes_written;
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 91341ec..a114d65 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3029,7 +3029,6 @@ out:
 	return err ? err : map->m_len;
 }
 
-#define EXT4_EXT_ZERO_LEN 7
 /*
  * This function is called by ext4_ext_map_blocks() if someone tries to write
  * to an uninitialized extent. It may result in splitting the uninitialized
@@ -3055,12 +3054,14 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 					   struct ext4_map_blocks *map,
 					   struct ext4_ext_path *path)
 {
+	struct ext4_sb_info *sbi;
 	struct ext4_extent_header *eh;
 	struct ext4_map_blocks split_map;
 	struct ext4_extent zero_ex;
 	struct ext4_extent *ex;
 	ext4_lblk_t ee_block, eof_block;
 	unsigned int ee_len, depth;
+	unsigned int zeroout_len;
 	int allocated;
 	int err = 0;
 	int split_flag = 0;
@@ -3069,6 +3070,8 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 		"block %llu, max_blocks %u\n", inode->i_ino,
 		(unsigned long long)map->m_lblk, map->m_len);
 
+	sbi = EXT4_SB(inode->i_sb);
+	zeroout_len = sbi->s_extent_zeroout_len;
 	eof_block = (inode->i_size + inode->i_sb->s_blocksize - 1) >>
 		inode->i_sb->s_blocksize_bits;
 	if (eof_block < map->m_lblk + map->m_len)
@@ -3168,8 +3171,8 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 	 */
 	split_flag |= ee_block + ee_len <= eof_block ? EXT4_EXT_MAY_ZEROOUT : 0;
 
-	/* If extent has less than 2*EXT4_EXT_ZERO_LEN zerout directly */
-	if (ee_len <= 2*EXT4_EXT_ZERO_LEN &&
+	/* If extent has less than 2*s_extent_zeroout_len zerout directly */
+	if (ee_len <= (2 * zeroout_len) &&
 	    (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
 		err = ext4_ext_zeroout(inode, ex);
 		if (err)
@@ -3195,7 +3198,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 	split_map.m_len = map->m_len;
 
 	if (allocated > map->m_len) {
-		if (allocated <= EXT4_EXT_ZERO_LEN &&
+		if (allocated <= zeroout_len &&
 		    (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
 			/* case 3 */
 			zero_ex.ee_block =
@@ -3209,7 +3212,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 			split_map.m_lblk = map->m_lblk;
 			split_map.m_len = allocated;
 		} else if ((map->m_lblk - ee_block + map->m_len <
-			   EXT4_EXT_ZERO_LEN) &&
+			   zeroout_len) &&
 			   (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
 			/* case 2 */
 			if (map->m_lblk != ee_block) {
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index eb7aa3e..ea7cb6b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2535,6 +2535,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
 EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
 EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
 EXT4_RW_ATTR_SBI_UI(max_writeback_mb_bump, s_max_writeback_mb_bump);
+EXT4_RW_ATTR_SBI_UI(extent_zeroout_len, s_extent_zeroout_len);
 EXT4_ATTR(trigger_fs_error, 0200, NULL, trigger_test_error);
 
 static struct attribute *ext4_attrs[] = {
@@ -2550,6 +2551,7 @@ static struct attribute *ext4_attrs[] = {
 	ATTR_LIST(mb_stream_req),
 	ATTR_LIST(mb_group_prealloc),
 	ATTR_LIST(max_writeback_mb_bump),
+	ATTR_LIST(extent_zeroout_len),
 	ATTR_LIST(trigger_fs_error),
 	NULL,
 };
@@ -3626,6 +3628,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 
 	sbi->s_stripe = ext4_get_stripe_size(sbi);
 	sbi->s_max_writeback_mb_bump = 128;
+	sbi->s_extent_zeroout_len = 256;
 
 	/*
 	 * set up enough so that it can read an inode
-- 
1.7.4.1

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