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Date: Mon, 20 Dec 2010 10:34:48 -0600
From: Eric Sandeen <sandeen@...hat.com>
To: "Theodore Ts'o" <tytso@....edu>
CC: Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: optimize ext4_check_dir_entry() with unlikely()
annotations
On 12/19/10 9:16 PM, Theodore Ts'o wrote:
> This function gets called a lot for large directories, and the answer
> is almost always "no, no, there's no problem". This means using
> unlikely() is a good thing.
testing bonnie++ file creates on a ramdisk should give a good idea
of how much or if this helps...
-Eric
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> ---
> fs/ext4/dir.c | 42 ++++++++++++++++++++++++------------------
> fs/ext4/ext4.h | 3 ++-
> fs/ext4/namei.c | 14 +++++++-------
> 3 files changed, 33 insertions(+), 26 deletions(-)
>
> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
> index ece76fb..bd5d74d 100644
> --- a/fs/ext4/dir.c
> +++ b/fs/ext4/dir.c
> @@ -60,7 +60,11 @@ static unsigned char get_dtype(struct super_block *sb, int filetype)
> return (ext4_filetype_table[filetype]);
> }
>
> -
> +/*
> + * Return 0 if the directory entry is OK, and 1 if there is a problem
> + *
> + * Note: this is the opposite of what ext2 and ext3 historically returned...
> + */
> int __ext4_check_dir_entry(const char *function, unsigned int line,
> struct inode *dir,
> struct ext4_dir_entry_2 *de,
> @@ -71,26 +75,28 @@ int __ext4_check_dir_entry(const char *function, unsigned int line,
> const int rlen = ext4_rec_len_from_disk(de->rec_len,
> dir->i_sb->s_blocksize);
>
> - if (rlen < EXT4_DIR_REC_LEN(1))
> + if (unlikely(rlen < EXT4_DIR_REC_LEN(1)))
> error_msg = "rec_len is smaller than minimal";
> - else if (rlen % 4 != 0)
> + else if (unlikely(rlen % 4 != 0))
> error_msg = "rec_len % 4 != 0";
> - else if (rlen < EXT4_DIR_REC_LEN(de->name_len))
> + else if (unlikely(rlen < EXT4_DIR_REC_LEN(de->name_len)))
> error_msg = "rec_len is too small for name_len";
> - else if (((char *) de - bh->b_data) + rlen > dir->i_sb->s_blocksize)
> + else if (unlikely(((char *) de - bh->b_data) + rlen >
> + dir->i_sb->s_blocksize))
> error_msg = "directory entry across blocks";
> - else if (le32_to_cpu(de->inode) >
> - le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count))
> + else if (unlikely(le32_to_cpu(de->inode) >
> + le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count)))
> error_msg = "inode out of bounds";
> + else
> + return 0;
>
> - if (error_msg != NULL)
> - ext4_error_inode(dir, function, line, bh->b_blocknr,
> - "bad entry in directory: %s - "
> - "offset=%u(%u), inode=%u, rec_len=%d, name_len=%d",
> - error_msg, (unsigned) (offset%bh->b_size), offset,
> - le32_to_cpu(de->inode),
> - rlen, de->name_len);
> - return error_msg == NULL ? 1 : 0;
> + ext4_error_inode(dir, function, line, bh->b_blocknr,
> + "bad entry in directory: %s - "
> + "offset=%u(%u), inode=%u, rec_len=%d, name_len=%d",
> + error_msg, (unsigned) (offset%bh->b_size), offset,
> + le32_to_cpu(de->inode),
> + rlen, de->name_len);
> + return 1;
> }
>
> static int ext4_readdir(struct file *filp,
> @@ -194,8 +200,8 @@ revalidate:
> while (!error && filp->f_pos < inode->i_size
> && offset < sb->s_blocksize) {
> de = (struct ext4_dir_entry_2 *) (bh->b_data + offset);
> - if (!ext4_check_dir_entry(inode, de,
> - bh, offset)) {
> + if (ext4_check_dir_entry(inode, de,
> + bh, offset)) {
> /*
> * On error, skip the f_pos to the next block
> */
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 17baecb..49f1cea 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1639,7 +1639,8 @@ extern int __ext4_check_dir_entry(const char *, unsigned int, struct inode *,
> struct ext4_dir_entry_2 *,
> struct buffer_head *, unsigned int);
> #define ext4_check_dir_entry(dir, de, bh, offset) \
> - __ext4_check_dir_entry(__func__, __LINE__, (dir), (de), (bh), (offset))
> + unlikely(__ext4_check_dir_entry(__func__, __LINE__, (dir), (de), \
> + (bh), (offset)))
> extern int ext4_htree_store_dirent(struct file *dir_file, __u32 hash,
> __u32 minor_hash,
> struct ext4_dir_entry_2 *dirent);
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 2030864..e275464 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -581,9 +581,9 @@ static int htree_dirblock_to_tree(struct file *dir_file,
> dir->i_sb->s_blocksize -
> EXT4_DIR_REC_LEN(0));
> for (; de < top; de = ext4_next_entry(de, dir->i_sb->s_blocksize)) {
> - if (!ext4_check_dir_entry(dir, de, bh,
> - (block<<EXT4_BLOCK_SIZE_BITS(dir->i_sb))
> - +((char *)de - bh->b_data))) {
> + if (ext4_check_dir_entry(dir, de, bh,
> + (block<<EXT4_BLOCK_SIZE_BITS(dir->i_sb))
> + + ((char *)de - bh->b_data))) {
> /* On error, skip the f_pos to the next block. */
> dir_file->f_pos = (dir_file->f_pos |
> (dir->i_sb->s_blocksize - 1)) + 1;
> @@ -820,7 +820,7 @@ static inline int search_dirblock(struct buffer_head *bh,
> if ((char *) de + namelen <= dlimit &&
> ext4_match (namelen, name, de)) {
> /* found a match - just to be sure, do a full check */
> - if (!ext4_check_dir_entry(dir, de, bh, offset))
> + if (ext4_check_dir_entry(dir, de, bh, offset))
> return -1;
> *res_dir = de;
> return 1;
> @@ -1269,7 +1269,7 @@ static int add_dirent_to_buf(handle_t *handle, struct dentry *dentry,
> de = (struct ext4_dir_entry_2 *)bh->b_data;
> top = bh->b_data + blocksize - reclen;
> while ((char *) de <= top) {
> - if (!ext4_check_dir_entry(dir, de, bh, offset))
> + if (ext4_check_dir_entry(dir, de, bh, offset))
> return -EIO;
> if (ext4_match(namelen, name, de))
> return -EEXIST;
> @@ -1636,7 +1636,7 @@ static int ext4_delete_entry(handle_t *handle,
> pde = NULL;
> de = (struct ext4_dir_entry_2 *) bh->b_data;
> while (i < bh->b_size) {
> - if (!ext4_check_dir_entry(dir, de, bh, i))
> + if (ext4_check_dir_entry(dir, de, bh, i))
> return -EIO;
> if (de == de_del) {
> BUFFER_TRACE(bh, "get_write_access");
> @@ -1919,7 +1919,7 @@ static int empty_dir(struct inode *inode)
> }
> de = (struct ext4_dir_entry_2 *) bh->b_data;
> }
> - if (!ext4_check_dir_entry(inode, de, bh, offset)) {
> + if (ext4_check_dir_entry(inode, de, bh, offset)) {
> de = (struct ext4_dir_entry_2 *)(bh->b_data +
> sb->s_blocksize);
> offset = (offset | (sb->s_blocksize - 1)) + 1;
--
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