ext4: Use a hash of the topdir directory name for the Orlov parent group

Instead of using a random number to determine the goal parent grop for
the Orlov top directories, use a hash of the directory name.  This
allows for repeatable results when trying to benchmark filesystem
layout algorithms.

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

1 files changed, 14 insertions, 5 deletions

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 7d502f3be914..3f98ee712ff4 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -470,7 +470,8 @@ void get_orlov_stats(struct super_block *sb, ext4_group_t g,
  */
 
 static int find_group_orlov(struct super_block *sb, struct inode *parent,
-                            ext4_group_t *group, int mode)
+                            ext4_group_t *group, int mode,
+                            const struct qstr *qstr)
 {
         ext4_group_t parent_group = EXT4_I(parent)->i_block_group;
         struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -485,6 +486,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
         struct ext4_group_desc *desc;
         struct orlov_stats stats;
         int flex_size = ext4_flex_bg_size(sbi);
+        struct dx_hash_info hinfo;
 
         ngroups = real_ngroups;
         if (flex_size > 1) {
@@ -506,7 +508,13 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
                 int best_ndir = inodes_per_group;
                 int ret = -1;
 
-                get_random_bytes(&grp, sizeof(grp));
+                if (qstr) {
+                        hinfo.hash_version = DX_HASH_HALF_MD4;
+                        hinfo.seed = sbi->s_hash_seed;
+                        ext4fs_dirhash(qstr->name, qstr->len, &hinfo);
+                        grp = hinfo.hash;
+                } else
+                        get_random_bytes(&grp, sizeof(grp));
                 parent_group = (unsigned)grp % ngroups;
                 for (i = 0; i < ngroups; i++) {
                         g = (parent_group + i) % ngroups;
@@ -649,7 +657,7 @@ static int find_group_other(struct super_block *sb, struct inode *parent,
                 *group = parent_group + flex_size;
                 if (*group > ngroups)
                         *group = 0;
-                return find_group_orlov(sb, parent, group, mode);
+                return find_group_orlov(sb, parent, group, mode, 0);
         }
 
         /*
@@ -790,7 +798,8 @@ err_ret:
  * For other inodes, search forward from the parent directory's block
  * group to find a free inode.
  */
-struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode)
+struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode,
+                             const struct qstr *qstr)
 {
         struct super_block *sb;
         struct buffer_head *inode_bitmap_bh = NULL;
@@ -839,7 +848,7 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode)
                 if (test_opt(sb, OLDALLOC))
                         ret2 = find_group_dir(sb, dir, &group);
                 else
-                        ret2 = find_group_orlov(sb, dir, &group, mode);
+                        ret2 = find_group_orlov(sb, dir, &group, mode, qstr);
         } else
                 ret2 = find_group_other(sb, dir, &group, mode);