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>
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 7d502f3..3f98ee7 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -470,7 +470,8 @@
*/
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 @@
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 @@
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 @@
*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 @@
* 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 @@
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);