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Date: Wed, 27 Mar 2013 16:35:40 +0100
From: Lukas Czerner <lczerner@...hat.com>
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu, Lukas Czerner <lczerner@...hat.com>
Subject: [PATCH 1/2 v3] ext4: Make ext4_block_in_group() much more efficient
Currently in when getting the block group number for a particular block
in ext4_block_in_group() we're using ext4_get_group_no_and_offset()
which uses do_div() to get the block group and the remainer which is
offset within the group.
We don't need all of that in ext4_block_in_group() as we only need to
figure out the group number.
This commit changes ext4_block_in_group() to calculate group number
directly. This shows as a big improvement with regards to cpu
utilization. Measuring fallocate -l 15T on fresh file system with perf
showed that 23% of cpu time was spend in the
ext4_get_group_no_and_offset(). With this change it completely
disappears from the list only bumping the occurrence of
ext4_init_block_bitmap() which is the biggest user of
ext4_block_in_group() by 4%. As the result of this change on my system
the fallocate call was approx. 10% faster.
However since there is '-g' option in mkfs which allow us setting
different groups size (mostly for developers) I've introduced new per
file system flag whether we have a standard block group size or not. The
flag is used to determine whether we can use the bit shift optimization
or not.
Signed-off-by: Lukas Czerner <lczerner@...hat.com>
---
v2: Add sbi flag if there is standard group size
v3: Use test_opt2/set_opt2
fs/ext4/balloc.c | 22 ++++++++++++++++------
fs/ext4/ext4.h | 10 +++++++++-
fs/ext4/super.c | 4 ++++
3 files changed, 29 insertions(+), 7 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 92e68b3..d6babf9 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -49,14 +49,24 @@ void ext4_get_group_no_and_offset(struct super_block *sb, ext4_fsblk_t blocknr,
}
-static int ext4_block_in_group(struct super_block *sb, ext4_fsblk_t block,
- ext4_group_t block_group)
+/*
+ * Check whether the 'block' lives within the 'block_group'. Returns 1 if so
+ * and 0 otherwise.
+ */
+static inline int ext4_block_in_group(struct super_block *sb,
+ ext4_fsblk_t block,
+ ext4_group_t block_group)
{
ext4_group_t actual_group;
- ext4_get_group_no_and_offset(sb, block, &actual_group, NULL);
- if (actual_group == block_group)
- return 1;
- return 0;
+
+ if (test_opt2(sb, STD_GROUP_SIZE))
+ actual_group =
+ (le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block) +
+ block) >>
+ (EXT4_BLOCK_SIZE_BITS(sb) + EXT4_CLUSTER_BITS(sb) + 3);
+ else
+ ext4_get_group_no_and_offset(sb, block, &actual_group, NULL);
+ return (actual_group == block_group) ? 1 : 0;
}
/* Return the number of clusters used for file system metadata; this
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 167ff56..87572c1 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -949,7 +949,7 @@ struct ext4_inode_info {
#define EXT2_FLAGS_TEST_FILESYS 0x0004 /* to test development code */
/*
- * Mount flags
+ * Mount flags set via mount options or defaults
*/
#define EXT4_MOUNT_GRPID 0x00004 /* Create files with directory's group */
#define EXT4_MOUNT_DEBUG 0x00008 /* Some debugging messages */
@@ -981,8 +981,16 @@ struct ext4_inode_info {
#define EXT4_MOUNT_DISCARD 0x40000000 /* Issue DISCARD requests */
#define EXT4_MOUNT_INIT_INODE_TABLE 0x80000000 /* Initialize uninitialized itables */
+/*
+ * Mount flags set either automatically (could not be set by mount option)
+ * based on per file system feature or property or in special cases such as
+ * distinguishing between explicit mount option definition and default.
+ */
#define EXT4_MOUNT2_EXPLICIT_DELALLOC 0x00000001 /* User explicitly
specified delalloc */
+#define EXT4_MOUNT2_STD_GROUP_SIZE 0x00000002 /* We have standard group
+ size of blocksize * 8
+ blocks */
#define clear_opt(sb, opt) EXT4_SB(sb)->s_mount_opt &= \
~EXT4_MOUNT_##opt
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d1ee6a8..5430630 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3522,6 +3522,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
sbi->s_addr_per_block_bits = ilog2(EXT4_ADDR_PER_BLOCK(sb));
sbi->s_desc_per_block_bits = ilog2(EXT4_DESC_PER_BLOCK(sb));
+ /* Do we have standard group size of blocksize * 8 blocks ? */
+ if (sbi->s_blocks_per_group == blocksize << 3)
+ set_opt2(sb, STD_GROUP_SIZE);
+
for (i = 0; i < 4; i++)
sbi->s_hash_seed[i] = le32_to_cpu(es->s_hash_seed[i]);
sbi->s_def_hash_version = es->s_def_hash_version;
--
1.7.7.6
--
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