[PATCH 6/7] repair: convert the dir byaddr hash to a radix tree

Dave Chinner
2021-03-19T01:34:54Z

From: Dave Chinner <dchinner@redhat.com>

Phase 6 uses a hash table to track the data segment addresses of the
entries it has seen in a directory. This is indexed by the offset
into the data segment for the dirent, and is used to check if the
entry exists, is a duplicate or has a bad hash value. The lookup
operations involve walking long hash chains on large directories and
they are done for every entry in the directory. This means certain
operations have O(n^2) scalability (or worse!) and hence hurt on
very large directories.

It is also used to determine if the directory has unseen entries,
which involves a full hash traversal that is very expensive on large
directories. Hence the directory checking for unseen ends up being
roughly a O(n^2 + n) algorithm.

Switch the byaddr indexing to a radix tree. While a radix tree will
burn more memory than the linked list, it gives us O(log n) lookup
operations instead of O(n) on large directories, and use for tags
gives us O(1) determination of whether all entries have been seen or
not. This brings the "entry seen" algorithm scalability back to
O(nlog n) and so is a major improvement for processing large
directories.

Given a filesystem with 10M empty files in a single directory, we
see:

5.6.0:

97.56% xfs_repair [.] dir_hash_add.lto_priv.0
0.38% xfs_repair [.] avl_ino_start.lto_priv.0
0.37% libc-2.31.so [.] malloc
0.34% xfs_repair [.] longform_dir2_entry_check_data.lto_priv.0

Phase 6: 10/22 12:07:13 10/22 12:10:51 3 minutes, 38 seconds

Patched:

97.11% xfs_repair [.] dir_hash_add
0.38% xfs_repair [.] longform_dir2_entry_check_data
0.34% libc-2.31.so [.] __libc_calloc
0.32% xfs_repair [.] avl_ino_start

Phase 6: 10/22 12:11:40 10/22 12:14:28 2 minutes, 48 seconds

So there's some improvement, but we are clearly still CPU bound due
to the O(n^2) scalability of the duplicate name checking algorithm.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
libfrog/radix-tree.c | 46 +++++++++
repair/phase6.c | 222 ++++++++++++++++++++-----------------------
2 files changed, 148 insertions(+), 120 deletions(-)

diff --git a/libfrog/radix-tree.c b/libfrog/radix-tree.c
index c1c74876964c..261fc2487de9 100644
--- a/libfrog/radix-tree.c
+++ b/libfrog/radix-tree.c
@@ -312,6 +312,52 @@ void *radix_tree_lookup_first(struct radix_tree_root *root, unsigned long *index

#ifdef RADIX_TREE_TAGS

+/**
+ * radix_tree_tag_get - get a tag on a radix tree node
+ * @root: radix tree root
+ * @index: index key
+ * @tag: tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ * Return values:
+ *
+ * 0: tag not present or not set
+ * 1: tag set
+ *
+ * Note that the return value of this function may not be relied on, even if
+ * the RCU lock is held, unless tag modification and node deletion are excluded
+ * from concurrency.
+ */
+int radix_tree_tag_get(struct radix_tree_root *root,
+ unsigned long index, unsigned int tag)
+{
+ unsigned int height, shift;
+ struct radix_tree_node *slot;
+
+ height = root->height;
+ if (index > radix_tree_maxindex(height))
+ return 0;
+
+ shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
+ slot = root->rnode;
+
+ while (height > 0) {
+ int offset;
+
+ if (slot == NULL)
+ return 0;
+
+ offset = (index >> shift) & RADIX_TREE_MAP_MASK;
+ if (!tag_get(slot, tag, offset))
+ return 0;
+
+ slot = slot->slots[offset];
+ ASSERT(slot != NULL);
+ shift -= RADIX_TREE_MAP_SHIFT;
+ height--;
+ }
+ return 1;
+}
+
/**
* radix_tree_tag_set - set a tag on a radix tree node
* @root: radix tree root
diff --git a/repair/phase6.c b/repair/phase6.c
index 440b6a2982df..a432856cca52 100644
--- a/repair/phase6.c
+++ b/repair/phase6.c
@@ -66,8 +66,7 @@ add_dotdot_update(
* and whether their leaf entry has been seen. Also used for name
* duplicate checking and rebuilding step if required.
*/
-typedef struct dir_hash_ent {
- struct dir_hash_ent *nextbyaddr; /* next in addr bucket */
+struct dir_hash_ent {
struct dir_hash_ent *nextbyhash; /* next in name bucket */
struct dir_hash_ent *nextbyorder; /* next in order added */
xfs_dahash_t hashval; /* hash value of name */
@@ -76,18 +75,19 @@ typedef struct dir_hash_ent {
short junkit; /* name starts with / */
short seen; /* have seen leaf entry */
struct xfs_name name;
-} dir_hash_ent_t;
+};

-typedef struct dir_hash_tab {
+struct dir_hash_tab {
int size; /* size of hash tables */
- dir_hash_ent_t *first; /* ptr to first added entry */
- dir_hash_ent_t *last; /* ptr to last added entry */
- dir_hash_ent_t **byhash; /* ptr to name hash buckets */
- dir_hash_ent_t **byaddr; /* ptr to addr hash buckets */
-} dir_hash_tab_t;
+ struct dir_hash_ent *first; /* ptr to first added entry */
+ struct dir_hash_ent *last; /* ptr to last added entry */
+ struct dir_hash_ent **byhash; /* ptr to name hash buckets */
+#define HT_UNSEEN 1
+ struct radix_tree_root byaddr;
+};

#define DIR_HASH_TAB_SIZE(n) \
- (sizeof(dir_hash_tab_t) + (sizeof(dir_hash_ent_t *) * (n) * 2))
+ (sizeof(struct dir_hash_tab) + (sizeof(struct dir_hash_ent *) * (n)))
#define DIR_HASH_FUNC(t,a) ((a) % (t)->size)

/*
@@ -154,8 +154,8 @@ dir_read_buf(
*/
static int
dir_hash_add(
- xfs_mount_t *mp,
- dir_hash_tab_t *hashtab,
+ struct xfs_mount *mp,
+ struct dir_hash_tab *hashtab,
uint32_t addr,
xfs_ino_t inum,
int namelen,
@@ -163,19 +163,18 @@ dir_hash_add(
uint8_t ftype)
{
xfs_dahash_t hash = 0;
- int byaddr;
int byhash = 0;
- dir_hash_ent_t *p;
+ struct dir_hash_ent *p;
int dup;
short junk;
struct xfs_name xname;
+ int error;

xname.name = name;
xname.len = namelen;
xname.type = ftype;

junk = name[0] == '/';
- byaddr = DIR_HASH_FUNC(hashtab, addr);
dup = 0;

if (!junk) {
@@ -205,8 +204,14 @@ dir_hash_add(
do_error(_("malloc failed in dir_hash_add (%zu bytes)\n"),
sizeof(*p));

- p->nextbyaddr = hashtab->byaddr[byaddr];
- hashtab->byaddr[byaddr] = p;
+ error = radix_tree_insert(&hashtab->byaddr, addr, p);
+ if (error == EEXIST) {
+ do_warn(_("duplicate addrs %u in directory!\n"), addr);
+ free(p);
+ return 0;
+ }
+ radix_tree_tag_set(&hashtab->byaddr, addr, HT_UNSEEN);
+
if (hashtab->last)
hashtab->last->nextbyorder = p;
else
@@ -232,33 +237,14 @@ dir_hash_add(
return !dup;
}

-/*
- * checks to see if any data entries are not in the leaf blocks
- */
-static int
-dir_hash_unseen(
- dir_hash_tab_t *hashtab)
-{
- int i;
- dir_hash_ent_t *p;
-
- for (i = 0; i < hashtab->size; i++) {
- for (p = hashtab->byaddr[i]; p; p = p->nextbyaddr) {
- if (p->seen == 0)
- return 1;
- }
- }
- return 0;
-}
-
static int
dir_hash_check(
- dir_hash_tab_t *hashtab,
- xfs_inode_t *ip,
- int seeval)
+ struct dir_hash_tab *hashtab,
+ struct xfs_inode *ip,
+ int seeval)
{
- static char *seevalstr[DIR_HASH_CK_TOTAL];
- static int done;
+ static char *seevalstr[DIR_HASH_CK_TOTAL];
+ static int done;

if (!done) {
seevalstr[DIR_HASH_CK_OK] = _("ok");
@@ -270,7 +256,8 @@ dir_hash_check(
done = 1;
}

- if (seeval == DIR_HASH_CK_OK && dir_hash_unseen(hashtab))
+ if (seeval == DIR_HASH_CK_OK &&
+ radix_tree_tagged(&hashtab->byaddr, HT_UNSEEN))
seeval = DIR_HASH_CK_NOLEAF;
if (seeval == DIR_HASH_CK_OK)
return 0;
@@ -285,27 +272,28 @@ dir_hash_check(

static void
dir_hash_done(
- dir_hash_tab_t *hashtab)
+ struct dir_hash_tab *hashtab)
{
- int i;
- dir_hash_ent_t *n;
- dir_hash_ent_t *p;
+ int i;
+ struct dir_hash_ent *n;
+ struct dir_hash_ent *p;

for (i = 0; i < hashtab->size; i++) {
- for (p = hashtab->byaddr[i]; p; p = n) {
- n = p->nextbyaddr;
+ for (p = hashtab->byhash[i]; p; p = n) {
+ n = p->nextbyhash;
+ radix_tree_delete(&hashtab->byaddr, p->address);
free(p);
}
}
free(hashtab);
}

-static dir_hash_tab_t *
+static struct dir_hash_tab *
dir_hash_init(
- xfs_fsize_t size)
+ xfs_fsize_t size)
{
- dir_hash_tab_t *hashtab;
- int hsize;
+ struct dir_hash_tab *hashtab;
+ int hsize;

hsize = size / (16 * 4);
if (hsize > 65536)
@@ -315,51 +303,43 @@ dir_hash_init(
if ((hashtab = calloc(DIR_HASH_TAB_SIZE(hsize), 1)) == NULL)
do_error(_("calloc failed in dir_hash_init\n"));
hashtab->size = hsize;
- hashtab->byhash = (dir_hash_ent_t**)((char *)hashtab +
- sizeof(dir_hash_tab_t));
- hashtab->byaddr = (dir_hash_ent_t**)((char *)hashtab +
- sizeof(dir_hash_tab_t) + sizeof(dir_hash_ent_t*) * hsize);
+ hashtab->byhash = (struct dir_hash_ent **)((char *)hashtab +
+ sizeof(struct dir_hash_tab));
+ INIT_RADIX_TREE(&hashtab->byaddr, 0);
return hashtab;
}

static int
dir_hash_see(
- dir_hash_tab_t *hashtab,
+ struct dir_hash_tab *hashtab,
xfs_dahash_t hash,
xfs_dir2_dataptr_t addr)
{
- int i;
- dir_hash_ent_t *p;
+ struct dir_hash_ent *p;

- i = DIR_HASH_FUNC(hashtab, addr);
- for (p = hashtab->byaddr[i]; p; p = p->nextbyaddr) {
- if (p->address != addr)
- continue;
- if (p->seen)
- return DIR_HASH_CK_DUPLEAF;
- if (p->junkit == 0 && p->hashval != hash)
- return DIR_HASH_CK_BADHASH;
- p->seen = 1;
- return DIR_HASH_CK_OK;
- }
- return DIR_HASH_CK_NODATA;
+ p = radix_tree_lookup(&hashtab->byaddr, addr);
+ if (!p)
+ return DIR_HASH_CK_NODATA;
+ if (!radix_tree_tag_get(&hashtab->byaddr, addr, HT_UNSEEN))
+ return DIR_HASH_CK_DUPLEAF;
+ if (p->junkit == 0 && p->hashval != hash)
+ return DIR_HASH_CK_BADHASH;
+ radix_tree_tag_clear(&hashtab->byaddr, addr, HT_UNSEEN);
+ return DIR_HASH_CK_OK;
}

static void
dir_hash_update_ftype(
- dir_hash_tab_t *hashtab,
+ struct dir_hash_tab *hashtab,
xfs_dir2_dataptr_t addr,
uint8_t ftype)
{
- int i;
- dir_hash_ent_t *p;
+ struct dir_hash_ent *p;

- i = DIR_HASH_FUNC(hashtab, addr);
- for (p = hashtab->byaddr[i]; p; p = p->nextbyaddr) {
- if (p->address != addr)
- continue;
- p->name.type = ftype;
- }
+ p = radix_tree_lookup(&hashtab->byaddr, addr);
+ if (!p)
+ return;
+ p->name.type = ftype;
}

/*
@@ -368,7 +348,7 @@ dir_hash_update_ftype(
*/
static int
dir_hash_see_all(
- dir_hash_tab_t *hashtab,
+ struct dir_hash_tab *hashtab,
xfs_dir2_leaf_entry_t *ents,
int count,
int stale)
@@ -1222,19 +1202,19 @@ dir_binval(

static void
longform_dir2_rebuild(
- xfs_mount_t *mp,
+ struct xfs_mount *mp,
xfs_ino_t ino,
- xfs_inode_t *ip,
- ino_tree_node_t *irec,
+ struct xfs_inode *ip,
+ struct ino_tree_node *irec,
int ino_offset,
- dir_hash_tab_t *hashtab)
+ struct dir_hash_tab *hashtab)
{
int error;
int nres;
- xfs_trans_t *tp;
+ struct xfs_trans *tp;
xfs_fileoff_t lastblock;
- xfs_inode_t pip;
- dir_hash_ent_t *p;
+ struct xfs_inode pip;
+ struct dir_hash_ent *p;
int done = 0;

/*
@@ -1393,14 +1373,14 @@ _("directory shrink failed (%d)\n"), error);
*/
static void
longform_dir2_entry_check_data(
- xfs_mount_t *mp,
- xfs_inode_t *ip,
+ struct xfs_mount *mp,
+ struct xfs_inode *ip,
int *num_illegal,
int *need_dot,
- ino_tree_node_t *current_irec,
+ struct ino_tree_node *current_irec,
int current_ino_offset,
struct xfs_buf *bp,
- dir_hash_tab_t *hashtab,
+ struct dir_hash_tab *hashtab,
freetab_t **freetabp,
xfs_dablk_t da_bno,
int isblock)
@@ -1927,10 +1907,10 @@ check_dir3_header(
*/
static int
longform_dir2_check_leaf(
- xfs_mount_t *mp,
- xfs_inode_t *ip,
- dir_hash_tab_t *hashtab,
- freetab_t *freetab)
+ struct xfs_mount *mp,
+ struct xfs_inode *ip,
+ struct dir_hash_tab *hashtab,
+ struct freetab *freetab)
{
int badtail;
__be16 *bestsp;
@@ -2012,10 +1992,10 @@ longform_dir2_check_leaf(
*/
static int
longform_dir2_check_node(
- xfs_mount_t *mp,
- xfs_inode_t *ip,
- dir_hash_tab_t *hashtab,
- freetab_t *freetab)
+ struct xfs_mount *mp,
+ struct xfs_inode *ip,
+ struct dir_hash_tab *hashtab,
+ struct freetab *freetab)
{
struct xfs_buf *bp;
xfs_dablk_t da_bno;
@@ -2187,14 +2167,15 @@ longform_dir2_check_node(
* (ie. get libxfs to do all the grunt work)
*/
static void
-longform_dir2_entry_check(xfs_mount_t *mp,
- xfs_ino_t ino,
- xfs_inode_t *ip,
- int *num_illegal,
- int *need_dot,
- ino_tree_node_t *irec,
- int ino_offset,
- dir_hash_tab_t *hashtab)
+longform_dir2_entry_check(
+ struct xfs_mount *mp,
+ xfs_ino_t ino,
+ struct xfs_inode *ip,
+ int *num_illegal,
+ int *need_dot,
+ struct ino_tree_node *irec,
+ int ino_offset,
+ struct dir_hash_tab *hashtab)
{
struct xfs_buf *bp;
xfs_dablk_t da_bno;
@@ -2397,13 +2378,14 @@ shortform_dir2_junk(
}

static void
-shortform_dir2_entry_check(xfs_mount_t *mp,
- xfs_ino_t ino,
- xfs_inode_t *ip,
- int *ino_dirty,
- ino_tree_node_t *current_irec,
- int current_ino_offset,
- dir_hash_tab_t *hashtab)
+shortform_dir2_entry_check(
+ struct xfs_mount *mp,
+ xfs_ino_t ino,
+ struct xfs_inode *ip,
+ int *ino_dirty,
+ struct ino_tree_node *current_irec,
+ int current_ino_offset,
+ struct dir_hash_tab *hashtab)
{
xfs_ino_t lino;
xfs_ino_t parent;
@@ -2745,15 +2727,15 @@ _("entry \"%s\" (ino %" PRIu64 ") in dir %" PRIu64 " is a duplicate name"),
*/
static void
process_dir_inode(
- xfs_mount_t *mp,
+ struct xfs_mount *mp,
xfs_agnumber_t agno,
- ino_tree_node_t *irec,
+ struct ino_tree_node *irec,
int ino_offset)
{
xfs_ino_t ino;
- xfs_inode_t *ip;
- xfs_trans_t *tp;
- dir_hash_tab_t *hashtab;
+ struct xfs_inode *ip;
+ struct xfs_trans *tp;
+ struct dir_hash_tab *hashtab;
int need_dot;
int dirty, num_illegal, error, nres;

--
2.30.1