On Wed, 06 Nov 2024, Jeff Layton wrote: > nfsd currently only uses a single slot in the callback channel, which is > proving to be a bottleneck in some cases. Widen the callback channel to > a max of 32 slots (subject to the client's target_maxreqs value). > > Change the cb_holds_slot boolean to an integer that tracks the current > slot number (with -1 meaning "unassigned"). Move the callback slot > tracking info into the session. Add a new u32 that acts as a bitmap to > track which slots are in use, and a u32 to track the latest callback > target_slotid that the client reports. To protect the new fields, add > a new per-session spinlock (the se_lock). Fix nfsd41_cb_get_slot to always > search for the lowest slotid (using ffs()). > > Finally, convert the session->se_cb_seq_nr field into an array of > counters and add the necessary handling to ensure that the seqids get > reset at the appropriate times. > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> > --- > v3 has a bug that Olga hit in testing. This version should fix the wait > when the slot table is full. Olga, if you're able to test this one, it > would be much appreciated. > --- > Changes in v4: > - Fix the wait for a slot in nfsd41_cb_get_slot() > - Link to v3: https://lore.kernel.org/r/20241030-bcwide-v3-0-c2df49a26c45@xxxxxxxxxx > > Changes in v3: > - add patch to convert se_flags to single se_dead bool > - fix off-by-one bug in handling of NFSD_BC_SLOT_TABLE_MAX > - don't reject target highest slot value of 0 > - Link to v2: https://lore.kernel.org/r/20241029-bcwide-v2-1-e9010b6ef55d@xxxxxxxxxx > > Changes in v2: > - take cl_lock when fetching fields from session to be encoded > - use fls() instead of bespoke highest_unset_index() > - rename variables in several functions with more descriptive names > - clamp limit of for loop in update_cb_slot_table() > - re-add missing rpc_wake_up_queued_task() call > - fix slotid check in decode_cb_sequence4resok() > - add new per-session spinlock > --- > fs/nfsd/nfs4callback.c | 113 ++++++++++++++++++++++++++++++++++++------------- > fs/nfsd/nfs4state.c | 11 +++-- > fs/nfsd/state.h | 15 ++++--- > fs/nfsd/trace.h | 2 +- > 4 files changed, 101 insertions(+), 40 deletions(-) > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > index e38fa834b3d91333acf1425eb14c644e5d5f2601..47a678333907eaa92db305dada503704c34c15b2 100644 > --- a/fs/nfsd/nfs4callback.c > +++ b/fs/nfsd/nfs4callback.c > @@ -406,6 +406,19 @@ encode_cb_getattr4args(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr, > hdr->nops++; > } > > +static u32 highest_slotid(struct nfsd4_session *ses) > +{ > + u32 idx; > + > + spin_lock(&ses->se_lock); > + idx = fls(~ses->se_cb_slot_avail); > + if (idx > 0) > + --idx; > + idx = max(idx, ses->se_cb_highest_slot); > + spin_unlock(&ses->se_lock); > + return idx; > +} > + > /* > * CB_SEQUENCE4args > * > @@ -432,15 +445,35 @@ static void encode_cb_sequence4args(struct xdr_stream *xdr, > encode_sessionid4(xdr, session); > > p = xdr_reserve_space(xdr, 4 + 4 + 4 + 4 + 4); > - *p++ = cpu_to_be32(session->se_cb_seq_nr); /* csa_sequenceid */ > - *p++ = xdr_zero; /* csa_slotid */ > - *p++ = xdr_zero; /* csa_highest_slotid */ > + *p++ = cpu_to_be32(session->se_cb_seq_nr[cb->cb_held_slot]); /* csa_sequenceid */ > + *p++ = cpu_to_be32(cb->cb_held_slot); /* csa_slotid */ > + *p++ = cpu_to_be32(highest_slotid(session)); /* csa_highest_slotid */ > *p++ = xdr_zero; /* csa_cachethis */ > xdr_encode_empty_array(p); /* csa_referring_call_lists */ > > hdr->nops++; > } > > +static void update_cb_slot_table(struct nfsd4_session *ses, u32 target) > +{ > + /* No need to do anything if nothing changed */ > + if (likely(target == READ_ONCE(ses->se_cb_highest_slot))) > + return; > + > + spin_lock(&ses->se_lock); > + if (target > ses->se_cb_highest_slot) { > + int i; > + > + target = min(target, NFSD_BC_SLOT_TABLE_MAX); > + > + /* Growing the slot table. Reset any new sequences to 1 */ > + for (i = ses->se_cb_highest_slot + 1; i <= target; ++i) > + ses->se_cb_seq_nr[i] = 1; Where is the justification in the RFC for resetting the sequence numbers? The csr_target_highest_slotid from the client - which is the value passed as 'target' is defined as: the highest slot ID the client would prefer the server use on a future CB_SEQUENCE operation. This is not "the highest slot ID for which the client is remembering sequence numbers". If we can get rid of this, then I think the need for se_lock evaporates. Allocating a new slow would be do { idx = ffs(ses->se_cb_slot_avail) - 1; } while (is_valid(idx) && test_and_set_bit(idx, &ses->se_sb_slot_avail)); where is_valid(idX) is idx >= 0 && idx <= ses->se_sb_highest_slot > + } > + ses->se_cb_highest_slot = target; > + spin_unlock(&ses->se_lock); > +} > + > /* > * CB_SEQUENCE4resok > * > @@ -468,7 +501,7 @@ static int decode_cb_sequence4resok(struct xdr_stream *xdr, > struct nfsd4_session *session = cb->cb_clp->cl_cb_session; > int status = -ESERVERFAULT; > __be32 *p; > - u32 dummy; > + u32 seqid, slotid, target; > > /* > * If the server returns different values for sessionID, slotID or > @@ -484,21 +517,22 @@ static int decode_cb_sequence4resok(struct xdr_stream *xdr, > } > p += XDR_QUADLEN(NFS4_MAX_SESSIONID_LEN); > > - dummy = be32_to_cpup(p++); > - if (dummy != session->se_cb_seq_nr) { > + seqid = be32_to_cpup(p++); > + if (seqid != session->se_cb_seq_nr[cb->cb_held_slot]) { > dprintk("NFS: %s Invalid sequence number\n", __func__); > goto out; > } > > - dummy = be32_to_cpup(p++); > - if (dummy != 0) { > + slotid = be32_to_cpup(p++); > + if (slotid != cb->cb_held_slot) { > dprintk("NFS: %s Invalid slotid\n", __func__); > goto out; > } > > - /* > - * FIXME: process highest slotid and target highest slotid > - */ > + p++; // ignore current highest slot value > + > + target = be32_to_cpup(p++); > + update_cb_slot_table(session, target); > status = 0; > out: > cb->cb_seq_status = status; > @@ -1203,6 +1237,22 @@ void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn) > spin_unlock(&clp->cl_lock); > } > > +static int grab_slot(struct nfsd4_session *ses) > +{ > + int idx; > + > + spin_lock(&ses->se_lock); > + idx = ffs(ses->se_cb_slot_avail) - 1; > + if (idx < 0 || idx > ses->se_cb_highest_slot) { > + spin_unlock(&ses->se_lock); > + return -1; > + } > + /* clear the bit for the slot */ > + ses->se_cb_slot_avail &= ~BIT(idx); > + spin_unlock(&ses->se_lock); > + return idx; > +} > + > /* > * There's currently a single callback channel slot. > * If the slot is available, then mark it busy. Otherwise, set the > @@ -1211,28 +1261,32 @@ void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn) > static bool nfsd41_cb_get_slot(struct nfsd4_callback *cb, struct rpc_task *task) > { > struct nfs4_client *clp = cb->cb_clp; > + struct nfsd4_session *ses = clp->cl_cb_session; > > - if (!cb->cb_holds_slot && > - test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) { > + if (cb->cb_held_slot >= 0) > + return true; > + cb->cb_held_slot = grab_slot(ses); > + if (cb->cb_held_slot < 0) { > rpc_sleep_on(&clp->cl_cb_waitq, task, NULL); > /* Race breaker */ > - if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) { > - dprintk("%s slot is busy\n", __func__); > + cb->cb_held_slot = grab_slot(ses); > + if (cb->cb_held_slot < 0) > return false; > - } > rpc_wake_up_queued_task(&clp->cl_cb_waitq, task); > } > - cb->cb_holds_slot = true; > return true; > } > > static void nfsd41_cb_release_slot(struct nfsd4_callback *cb) > { > struct nfs4_client *clp = cb->cb_clp; > + struct nfsd4_session *ses = clp->cl_cb_session; > > - if (cb->cb_holds_slot) { > - cb->cb_holds_slot = false; > - clear_bit(0, &clp->cl_cb_slot_busy); > + if (cb->cb_held_slot >= 0) { > + spin_lock(&ses->se_lock); > + ses->se_cb_slot_avail |= BIT(cb->cb_held_slot); > + spin_unlock(&ses->se_lock); > + cb->cb_held_slot = -1; > rpc_wake_up_next(&clp->cl_cb_waitq); > } > } > @@ -1249,8 +1303,8 @@ static void nfsd41_destroy_cb(struct nfsd4_callback *cb) > } > > /* > - * TODO: cb_sequence should support referring call lists, cachethis, multiple > - * slots, and mark callback channel down on communication errors. > + * TODO: cb_sequence should support referring call lists, cachethis, > + * and mark callback channel down on communication errors. > */ > static void nfsd4_cb_prepare(struct rpc_task *task, void *calldata) > { > @@ -1292,7 +1346,7 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback > return true; > } > > - if (!cb->cb_holds_slot) > + if (cb->cb_held_slot < 0) > goto need_restart; > > /* This is the operation status code for CB_SEQUENCE */ > @@ -1306,10 +1360,10 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback > * If CB_SEQUENCE returns an error, then the state of the slot > * (sequence ID, cached reply) MUST NOT change. > */ > - ++session->se_cb_seq_nr; > + ++session->se_cb_seq_nr[cb->cb_held_slot]; > break; > case -ESERVERFAULT: > - ++session->se_cb_seq_nr; > + ++session->se_cb_seq_nr[cb->cb_held_slot]; > nfsd4_mark_cb_fault(cb->cb_clp); > ret = false; > break; > @@ -1335,17 +1389,16 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback > case -NFS4ERR_BADSLOT: > goto retry_nowait; > case -NFS4ERR_SEQ_MISORDERED: > - if (session->se_cb_seq_nr != 1) { > - session->se_cb_seq_nr = 1; > + if (session->se_cb_seq_nr[cb->cb_held_slot] != 1) { > + session->se_cb_seq_nr[cb->cb_held_slot] = 1; This is weird ... why do we reset the seq_nr to 1 when we get SEQ_MISORDERED?? Git logs don't shed any light :-( > goto retry_nowait; > } > break; > default: > nfsd4_mark_cb_fault(cb->cb_clp); > } > - nfsd41_cb_release_slot(cb); > - > trace_nfsd_cb_free_slot(task, cb); > + nfsd41_cb_release_slot(cb); > > if (RPC_SIGNALLED(task)) > goto need_restart; > @@ -1565,7 +1618,7 @@ void nfsd4_init_cb(struct nfsd4_callback *cb, struct nfs4_client *clp, > INIT_WORK(&cb->cb_work, nfsd4_run_cb_work); > cb->cb_status = 0; > cb->cb_need_restart = false; > - cb->cb_holds_slot = false; > + cb->cb_held_slot = -1; > } > > /** > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > index baf7994131fe1b0a4715174ba943fd2a9882aa12..75557e7cc9265517f51952563beaa4cfe8adcc3f 100644 > --- a/fs/nfsd/nfs4state.c > +++ b/fs/nfsd/nfs4state.c > @@ -2002,6 +2002,9 @@ static struct nfsd4_session *alloc_session(struct nfsd4_channel_attrs *fattrs, > } > > memcpy(&new->se_fchannel, fattrs, sizeof(struct nfsd4_channel_attrs)); > + new->se_cb_slot_avail = ~0U; > + new->se_cb_highest_slot = battrs->maxreqs - 1; > + spin_lock_init(&new->se_lock); > return new; > out_free: > while (i--) > @@ -2132,11 +2135,14 @@ static void init_session(struct svc_rqst *rqstp, struct nfsd4_session *new, stru > > INIT_LIST_HEAD(&new->se_conns); > > - new->se_cb_seq_nr = 1; > + atomic_set(&new->se_ref, 0); > new->se_dead = false; > new->se_cb_prog = cses->callback_prog; > new->se_cb_sec = cses->cb_sec; > - atomic_set(&new->se_ref, 0); > + > + for (idx = 0; idx < NFSD_BC_SLOT_TABLE_MAX; ++idx) > + new->se_cb_seq_nr[idx] = 1; That should be "<= NFSD_BC_SLOT_TABLE_MAX" I don't think *_MAX is a good choice of name. It is the maximum number of slots (no) or the maximum slot number (yes). I think *_SIZE would be a better name - the size of the table that we allocate. 32. Looking at where the const is used in current nfsd-next: target = min(target, NFSD_BC_SLOT_TABLE_SIZE - 1 new->se_cb_highest_slot = min(battrs->maxreqs, NFSD_BC_SLOT_TABLE_SIZE) - 1; for (idx = 0; idx < NFSD_BC_SLOT_TABLE_SIZE; ++idx) #define NFSD_BC_SLOT_TABLE_SIZE (sizeof(u32) * 8) u32 se_cb_seq_nr[NFSD_BC_SLOT_TABLE_SIZE]; which is a slight reduction in the number of "+/-1" adjustments. > + > idx = hash_sessionid(&new->se_sessionid); > list_add(&new->se_hash, &nn->sessionid_hashtbl[idx]); > spin_lock(&clp->cl_lock); > @@ -3159,7 +3165,6 @@ static struct nfs4_client *create_client(struct xdr_netobj name, > kref_init(&clp->cl_nfsdfs.cl_ref); > nfsd4_init_cb(&clp->cl_cb_null, clp, NULL, NFSPROC4_CLNT_CB_NULL); > clp->cl_time = ktime_get_boottime_seconds(); > - clear_bit(0, &clp->cl_cb_slot_busy); > copy_verf(clp, verf); > memcpy(&clp->cl_addr, sa, sizeof(struct sockaddr_storage)); > clp->cl_cb_session = NULL; > diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h > index d22e4f2c9039324a0953a9e15a3c255fb8ee1a44..848d023cb308f0b69916c4ee34b09075708f0de3 100644 > --- a/fs/nfsd/state.h > +++ b/fs/nfsd/state.h > @@ -71,8 +71,8 @@ struct nfsd4_callback { > struct work_struct cb_work; > int cb_seq_status; > int cb_status; > + int cb_held_slot; > bool cb_need_restart; > - bool cb_holds_slot; > }; > > struct nfsd4_callback_ops { > @@ -307,6 +307,9 @@ struct nfsd4_conn { > unsigned char cn_flags; > }; > > +/* Highest slot index that nfsd implements in NFSv4.1+ backchannel */ > +#define NFSD_BC_SLOT_TABLE_MAX (sizeof(u32) * 8 - 1) > + > /* > * Representation of a v4.1+ session. These are refcounted in a similar fashion > * to the nfs4_client. References are only taken when the server is actively > @@ -314,6 +317,10 @@ struct nfsd4_conn { > */ > struct nfsd4_session { > atomic_t se_ref; > + spinlock_t se_lock; > + u32 se_cb_slot_avail; /* bitmap of available slots */ > + u32 se_cb_highest_slot; /* highest slot client wants */ > + u32 se_cb_prog; > bool se_dead; > struct list_head se_hash; /* hash by sessionid */ > struct list_head se_perclnt; > @@ -322,8 +329,7 @@ struct nfsd4_session { > struct nfsd4_channel_attrs se_fchannel; > struct nfsd4_cb_sec se_cb_sec; > struct list_head se_conns; > - u32 se_cb_prog; > - u32 se_cb_seq_nr; > + u32 se_cb_seq_nr[NFSD_BC_SLOT_TABLE_MAX + 1]; > struct nfsd4_slot *se_slots[]; /* forward channel slots */ > }; > > @@ -457,9 +463,6 @@ struct nfs4_client { > */ > struct dentry *cl_nfsd_info_dentry; > > - /* for nfs41 callbacks */ > - /* We currently support a single back channel with a single slot */ > - unsigned long cl_cb_slot_busy; > struct rpc_wait_queue cl_cb_waitq; /* backchannel callers may */ > /* wait here for slots */ > struct net *net; > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h > index f318898cfc31614b5a84a4867e18c2b3a07122c9..a9c17186b6892f1df8d7f7b90e250c2913ab23fe 100644 > --- a/fs/nfsd/trace.h > +++ b/fs/nfsd/trace.h > @@ -1697,7 +1697,7 @@ TRACE_EVENT(nfsd_cb_free_slot, > __entry->cl_id = sid->clientid.cl_id; > __entry->seqno = sid->sequence; > __entry->reserved = sid->reserved; > - __entry->slot_seqno = session->se_cb_seq_nr; > + __entry->slot_seqno = session->se_cb_seq_nr[cb->cb_held_slot]; > ), > TP_printk(SUNRPC_TRACE_TASK_SPECIFIER > " sessionid=%08x:%08x:%08x:%08x new slot seqno=%u", > > --- > base-commit: 3c16aac09d20f9005fbb0e737b3ec520bbb5badd > change-id: 20241025-bcwide-6bd7e4b63db2 > > Best regards, > -- > Jeff Layton <jlayton@xxxxxxxxxx> > > NeilBrown
