bcachefs: is_ancestor bitmap

Further optimization for bch2_snapshot_is_ancestor(). We add a small
inline bitmap to snapshot_t, which indicates which of the next 128
snapshot IDs are ancestors of the current id - eliminating the last few
iterations of the loop in bch2_snapshot_is_ancestor().

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/subvolume.c b/fs/bcachefs/subvolume.c
index c2c2cfd74e71f92a6e81e4c284e8c256120318b6..cf8af617ac00d2302000642dc0c934c11217ca8b 100644 (file)
--- a/fs/bcachefs/subvolume.c
+++ b/fs/bcachefs/subvolume.c
@@ -28,17 +28,22 @@ static inline u32 get_ancestor_below(struct snapshot_table *t, u32 id, u32 ances
 bool bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
 {
        struct snapshot_table *t;
+       bool ret;
 
        EBUG_ON(c->curr_recovery_pass <= BCH_RECOVERY_PASS_check_snapshots);
 
        rcu_read_lock();
        t = rcu_dereference(c->snapshots);
 
-       while (id && id < ancestor)
+       while (id && id < ancestor - IS_ANCESTOR_BITMAP)
                id = get_ancestor_below(t, id, ancestor);
+
+       ret = id && id < ancestor
+               ? test_bit(ancestor - id - 1, __snapshot_t(t, id)->is_ancestor)
+               : id == ancestor;
        rcu_read_unlock();
 
-       return id == ancestor;
+       return ret;
 }
 
 static bool bch2_snapshot_is_ancestor_early(struct bch_fs *c, u32 id, u32 ancestor)
@@ -289,11 +294,12 @@ int bch2_mark_snapshot(struct btree_trans *trans,
 {
        struct bch_fs *c = trans->c;
        struct snapshot_t *t;
+       u32 id = new.k->p.offset;
        int ret = 0;
 
        mutex_lock(&c->snapshot_table_lock);
 
-       t = snapshot_t_mut(c, new.k->p.offset);
+       t = snapshot_t_mut(c, id);
        if (!t) {
                ret = -BCH_ERR_ENOMEM_mark_snapshot;
                goto err;
@@ -301,6 +307,7 @@ int bch2_mark_snapshot(struct btree_trans *trans,
 
        if (new.k->type == KEY_TYPE_snapshot) {
                struct bkey_s_c_snapshot s = bkey_s_c_to_snapshot(new);
+               u32 parent = id;
 
                t->parent       = le32_to_cpu(s.v->parent);
                t->children[0]  = le32_to_cpu(s.v->children[0]);
@@ -320,14 +327,14 @@ int bch2_mark_snapshot(struct btree_trans *trans,
                        t->skip[2]      = 0;
                }
 
+               while ((parent = bch2_snapshot_parent_early(c, parent)) &&
+                      parent - id - 1 < IS_ANCESTOR_BITMAP)
+                       __set_bit(parent - id - 1, t->is_ancestor);
+
                if (BCH_SNAPSHOT_DELETED(s.v))
                        set_bit(BCH_FS_HAVE_DELETED_SNAPSHOTS, &c->flags);
        } else {
-               t->parent       = 0;
-               t->children[0]  = 0;
-               t->children[1]  = 0;
-               t->subvol       = 0;
-               t->tree         = 0;
+               memset(t, 0, sizeof(*t));
        }
 err:
        mutex_unlock(&c->snapshot_table_lock);

diff --git a/fs/bcachefs/subvolume_types.h b/fs/bcachefs/subvolume_types.h
index c596e4270690baf4193b73d29c63b50c5351da5f..86833445af205643b81bd08b3b204005c7bee071 100644 (file)
--- a/fs/bcachefs/subvolume_types.h
+++ b/fs/bcachefs/subvolume_types.h
@@ -6,6 +6,8 @@
 
 typedef DARRAY(u32) snapshot_id_list;
 
+#define IS_ANCESTOR_BITMAP     128
+
 struct snapshot_t {
        u32                     parent;
        u32                     skip[3];
@@ -14,6 +16,7 @@ struct snapshot_t {
        u32                     subvol; /* Nonzero only if a subvolume points to this node: */
        u32                     tree;
        u32                     equiv;
+       unsigned long           is_ancestor[BITS_TO_LONGS(IS_ANCESTOR_BITMAP)];
 };
 
 struct snapshot_table {