[PATCH 2/5] ceph: replace the request_tree rbtree with an xarray keyed by r_tid.
From: Xiubo Li via B4 Relay
Date: Mon Jul 13 2026 - 05:51:55 EST
From: Xiubo Li <xiubo.li@xxxxxxxxx>
The xarray gives O(1) lookups by tid (vs O(log N) rbtree) and
uses internal RCU-based locking, eliminating mdsc->mutex as a
precondition for tree access and paving the way for lockless
xa_load() in the future. Iteration is also cleaner: xa_for_each()
and xa_find() replace the open-coded rb_first()/rb_next() walks.
Signed-off-by: Xiubo Li <xiubo.li@xxxxxxxxx>
---
fs/ceph/debugfs.c | 6 +--
fs/ceph/mds_client.c | 109 ++++++++++++++++++++++-----------------------------
fs/ceph/mds_client.h | 3 +-
3 files changed, 50 insertions(+), 68 deletions(-)
diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index 18eb5da03411..491ead3fe1c6 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -87,12 +87,12 @@ static int mdsc_show(struct seq_file *s, void *p)
struct ceph_fs_client *fsc = s->private;
struct ceph_mds_client *mdsc = fsc->mdsc;
struct ceph_mds_request *req;
- struct rb_node *rp;
+ unsigned long idx;
char *path;
mutex_lock(&mdsc->mutex);
- for (rp = rb_first(&mdsc->request_tree); rp; rp = rb_next(rp)) {
- req = rb_entry(rp, struct ceph_mds_request, r_node);
+ idx = 0;
+ xa_for_each(&mdsc->request_tree, idx, req) {
if (req->r_request && req->r_session)
seq_printf(s, "%lld\tmds%d\t", req->r_tid,
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 98d0a5baff70..909f909b64ed 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -1183,7 +1183,6 @@ void ceph_mdsc_release_request(struct kref *kref)
kmem_cache_free(ceph_mds_request_cachep, req);
}
-DEFINE_RB_FUNCS(request, struct ceph_mds_request, r_tid, r_node)
/*
* lookup session, bump ref if found.
@@ -1195,7 +1194,7 @@ lookup_get_request(struct ceph_mds_client *mdsc, u64 tid)
{
struct ceph_mds_request *req;
- req = lookup_request(&mdsc->request_tree, tid);
+ req = xa_load(&mdsc->request_tree, tid);
if (req)
ceph_mdsc_get_request(req);
@@ -1229,7 +1228,7 @@ static void __register_request(struct ceph_mds_client *mdsc,
}
doutc(cl, "%p tid %lld\n", req, req->r_tid);
ceph_mdsc_get_request(req);
- insert_request(&mdsc->request_tree, req);
+ xa_store(&mdsc->request_tree, req->r_tid, req, GFP_NOFS);
req->r_cred = get_current_cred();
if (!req->r_mnt_idmap)
@@ -1259,20 +1258,20 @@ static void __unregister_request(struct ceph_mds_client *mdsc,
list_del_init(&req->r_unsafe_item);
if (req->r_tid == atomic64_read(&mdsc->oldest_tid)) {
- struct rb_node *p = rb_next(&req->r_node);
+ unsigned long tidx = req->r_tid + 1;
+ struct ceph_mds_request *next_req;
+
atomic64_set(&mdsc->oldest_tid, 0);
- while (p) {
- struct ceph_mds_request *next_req =
- rb_entry(p, struct ceph_mds_request, r_node);
+ xa_for_each_start(&mdsc->request_tree, tidx, next_req, tidx) {
if (next_req->r_op != CEPH_MDS_OP_SETFILELOCK) {
- atomic64_set(&mdsc->oldest_tid, next_req->r_tid);
+ atomic64_set(&mdsc->oldest_tid,
+ next_req->r_tid);
break;
}
- p = rb_next(p);
}
}
- erase_request(&mdsc->request_tree, req);
+ xa_erase(&mdsc->request_tree, req->r_tid);
if (req->r_unsafe_dir) {
struct ceph_inode_info *ci = ceph_inode(req->r_unsafe_dir);
@@ -1829,7 +1828,7 @@ static void cleanup_session_requests(struct ceph_mds_client *mdsc,
{
struct ceph_client *cl = mdsc->fsc->client;
struct ceph_mds_request *req;
- struct rb_node *p;
+ unsigned long idx;
doutc(cl, "mds%d\n", session->s_mds);
mutex_lock(&mdsc->mutex);
@@ -1845,10 +1844,8 @@ static void cleanup_session_requests(struct ceph_mds_client *mdsc,
__unregister_request(mdsc, req);
}
/* zero r_attempts, so kick_requests() will re-send requests */
- p = rb_first(&mdsc->request_tree);
- while (p) {
- req = rb_entry(p, struct ceph_mds_request, r_node);
- p = rb_next(p);
+ idx = 0;
+ xa_for_each(&mdsc->request_tree, idx, req) {
if (req->r_session &&
req->r_session->s_mds == session->s_mds)
req->r_attempts = 0;
@@ -2732,7 +2729,6 @@ ceph_mdsc_create_request(struct ceph_mds_client *mdsc, int op, int mode)
req->r_fmode = -1;
req->r_feature_needed = -1;
kref_init(&req->r_kref);
- RB_CLEAR_NODE(&req->r_node);
INIT_LIST_HEAD(&req->r_wait);
init_completion(&req->r_completion);
init_completion(&req->r_safe_completion);
@@ -2752,10 +2748,9 @@ ceph_mdsc_create_request(struct ceph_mds_client *mdsc, int op, int mode)
*/
static struct ceph_mds_request *__get_oldest_req(struct ceph_mds_client *mdsc)
{
- if (RB_EMPTY_ROOT(&mdsc->request_tree))
- return NULL;
- return rb_entry(rb_first(&mdsc->request_tree),
- struct ceph_mds_request, r_node);
+ unsigned long idx = 0;
+
+ return xa_find(&mdsc->request_tree, &idx, ULONG_MAX, XA_PRESENT);
}
static inline u64 __get_oldest_tid(struct ceph_mds_client *mdsc)
@@ -3816,12 +3811,11 @@ static void kick_requests(struct ceph_mds_client *mdsc, int mds)
{
struct ceph_client *cl = mdsc->fsc->client;
struct ceph_mds_request *req;
- struct rb_node *p = rb_first(&mdsc->request_tree);
+ unsigned long idx;
doutc(cl, "kick_requests mds%d\n", mds);
- while (p) {
- req = rb_entry(p, struct ceph_mds_request, r_node);
- p = rb_next(p);
+ idx = 0;
+ xa_for_each(&mdsc->request_tree, idx, req) {
if (test_bit(CEPH_MDS_R_GOT_UNSAFE, &req->r_req_flags))
continue;
if (req->r_attempts > 0)
@@ -4654,7 +4648,7 @@ static void replay_unsafe_requests(struct ceph_mds_client *mdsc,
struct ceph_mds_session *session)
{
struct ceph_mds_request *req, *nreq;
- struct rb_node *p;
+ unsigned long idx;
doutc(mdsc->fsc->client, "mds%d\n", session->s_mds);
@@ -4666,10 +4660,8 @@ static void replay_unsafe_requests(struct ceph_mds_client *mdsc,
* also re-send old requests when MDS enters reconnect stage. So that MDS
* can process completed request in clientreplay stage.
*/
- p = rb_first(&mdsc->request_tree);
- while (p) {
- req = rb_entry(p, struct ceph_mds_request, r_node);
- p = rb_next(p);
+ idx = 0;
+ xa_for_each(&mdsc->request_tree, idx, req) {
if (test_bit(CEPH_MDS_R_GOT_UNSAFE, &req->r_req_flags))
continue;
if (req->r_attempts == 0)
@@ -5514,7 +5506,7 @@ static void ceph_mdsc_reset_workfn(struct work_struct *work)
*/
{
struct ceph_mds_request *req;
- struct rb_node *rn;
+ unsigned long idx;
u64 last_tid;
mutex_lock(&mdsc->mutex);
@@ -5522,14 +5514,12 @@ static void ceph_mdsc_reset_workfn(struct work_struct *work)
mutex_unlock(&mdsc->mutex);
mutex_lock(&mdsc->mutex);
- rn = rb_first(&mdsc->request_tree);
- while (rn) {
- req = rb_entry(rn, struct ceph_mds_request, r_node);
- if (req->r_tid > last_tid)
- break;
+ idx = 0;
+ while ((req = xa_find(&mdsc->request_tree, &idx, last_tid,
+ XA_PRESENT))) {
if (req->r_op == CEPH_MDS_OP_SETFILELOCK ||
!(req->r_op & CEPH_MDS_OP_WRITE)) {
- rn = rb_next(rn);
+ idx++;
continue;
}
ceph_mdsc_get_request(req);
@@ -5542,7 +5532,7 @@ static void ceph_mdsc_reset_workfn(struct work_struct *work)
ceph_mdsc_put_request(req);
if (time_after(jiffies, drain_deadline))
break;
- rn = rb_first(&mdsc->request_tree);
+ idx = 0; /* restart: tree may have changed */
}
mutex_unlock(&mdsc->mutex);
@@ -6268,7 +6258,7 @@ int ceph_mdsc_init(struct ceph_fs_client *fsc)
mdsc->snap_realms = RB_ROOT;
INIT_LIST_HEAD(&mdsc->snap_empty);
spin_lock_init(&mdsc->snap_empty_lock);
- mdsc->request_tree = RB_ROOT;
+ xa_init(&mdsc->request_tree);
INIT_DELAYED_WORK(&mdsc->delayed_work, delayed_work);
mdsc->last_renew_caps = jiffies;
INIT_LIST_HEAD(&mdsc->cap_delay_list);
@@ -6590,34 +6580,33 @@ static void flush_mdlog_and_wait_mdsc_unsafe_requests(struct ceph_mds_client *md
u64 want_tid)
{
struct ceph_client *cl = mdsc->fsc->client;
- struct ceph_mds_request *req = NULL, *nextreq;
+ struct ceph_mds_request *req;
struct ceph_mds_session *last_session = NULL;
- struct rb_node *n;
+ unsigned long idx;
mutex_lock(&mdsc->mutex);
doutc(cl, "want %lld\n", want_tid);
-restart:
- req = __get_oldest_req(mdsc);
- while (req && req->r_tid <= want_tid) {
- /* find next request */
- n = rb_next(&req->r_node);
- if (n)
- nextreq = rb_entry(n, struct ceph_mds_request, r_node);
- else
- nextreq = NULL;
- if (req->r_op != CEPH_MDS_OP_SETFILELOCK &&
- (req->r_op & CEPH_MDS_OP_WRITE)) {
+ idx = 0;
+ while ((req = xa_find(&mdsc->request_tree, &idx, want_tid,
+ XA_PRESENT))) {
+ u64 next_tid = req->r_tid + 1;
+
+ if (req->r_op == CEPH_MDS_OP_SETFILELOCK ||
+ !(req->r_op & CEPH_MDS_OP_WRITE)) {
+ idx = next_tid;
+ continue;
+ }
+
+ {
struct ceph_mds_session *s = req->r_session;
if (!s) {
- req = nextreq;
+ idx = next_tid;
continue;
}
/* write op */
ceph_mdsc_get_request(req);
- if (nextreq)
- ceph_mdsc_get_request(nextreq);
s = ceph_get_mds_session(s);
mutex_unlock(&mdsc->mutex);
@@ -6635,16 +6624,9 @@ static void flush_mdlog_and_wait_mdsc_unsafe_requests(struct ceph_mds_client *md
mutex_lock(&mdsc->mutex);
ceph_mdsc_put_request(req);
- if (!nextreq)
- break; /* next dne before, so we're done! */
- if (RB_EMPTY_NODE(&nextreq->r_node)) {
- /* next request was removed from tree */
- ceph_mdsc_put_request(nextreq);
- goto restart;
- }
- ceph_mdsc_put_request(nextreq); /* won't go away */
+ /* restart from the next tid; tree may have changed */
+ idx = next_tid;
}
- req = nextreq;
}
mutex_unlock(&mdsc->mutex);
ceph_put_mds_session(last_session);
@@ -6803,6 +6785,7 @@ static void ceph_mdsc_stop(struct ceph_mds_client *mdsc)
if (mdsc->mdsmap)
ceph_mdsmap_destroy(mdsc->mdsmap);
kfree(mdsc->sessions);
+ xa_destroy(&mdsc->request_tree);
ceph_caps_finalize(mdsc);
if (mdsc->s_cap_auths) {
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 3b614b5df18c..00ca993ed583 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -329,7 +329,6 @@ typedef int (*ceph_mds_request_wait_callback_t) (struct ceph_mds_client *mdsc,
*/
struct ceph_mds_request {
u64 r_tid; /* transaction id */
- struct rb_node r_node;
struct ceph_mds_client *r_mdsc;
struct kref r_kref;
@@ -534,7 +533,7 @@ struct ceph_mds_client {
u64 last_tid; /* most recent mds request */
atomic64_t oldest_tid; /* oldest incomplete mds request,
excluding setfilelock requests */
- struct rb_root request_tree; /* pending mds requests */
+ struct xarray request_tree; /* pending mds requests */
struct delayed_work delayed_work; /* delayed work */
unsigned long last_renew_caps; /* last time we renewed our caps */
struct list_head cap_delay_list; /* caps with delayed release */
--
2.53.0