ext4: optimize ext4_check_dir_entry() with unlikely() annotations
Theodore Ts'o [Mon, 20 Dec 2010 03:07:02 +0000 (22:07 -0500)]
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.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/dir.c
fs/ext4/ext4.h
fs/ext4/namei.c

index ece76fb..bd5d74d 100644 (file)
@@ -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
                                 */
index 17baecb..49f1cea 100644 (file)
@@ -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);
index 2030864..e275464 100644 (file)
@@ -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;