Re: [PATCH Version 4 4/7] NFSv4.1: dynamic session slots

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On Dec 11, 2011, at 8:14 AM, Benny Halevy wrote:

> Hi Andy,
> 
> I have some minor-ish comments inline below, but the whole
> hlist concept looks to me like it might incur pretty high overhead
> in cpu and memory caching.

I'd like to measure the difference. What is the recommended way?

> 
> Have you considered simply reallocating the slot table on grow
> and maybe on shrink below a certain threshold?

Because the slot pointer is placed in the response, we would have to drain the slot table to grow/shrink in this manner.

-->Andy

> 
> On 2011-11-09 20:58, andros@xxxxxxxxxx wrote:
>> From: Andy Adamson <andros@xxxxxxxxxx>
>> 
>> The session fore/backchannel slot tables implementation is changed from a
>> static array to an hlist hashed on slotid. Slotid's are values 0..N where N
>> is initially negotiated between the client and server via the CREATE_SESSION
>> call, and can be dynamically changed by the server during an active session.
>> 
>> When there are no allocated slots (mount), an initial number of session slots
>> is allocated equal to the inital number of dynamic rpc_slots
>> created upon transport creation (xprt->min_reqs).  Slots are then dynamically
>> allocated as needed upto the CREATE_SESSION negotiated max_reqs value.
>> 
>> For session reset the session is drained (inactive). The (old) session has
>> allocated slot tables which we will reuse. nfs4_reduce_slots_locked is called
>> and only reduces the allocated_slots if the new max_reqs negotiated by the
>> reset CREATE_SESSION is less than the number of allocated_slots. The resultant
>> slot table is then re-initialized.
>> 
>> CB_SLOT_RECALL is changed only in that it now shares code with session
>> reset - it also calls nfs4_reduce_slots_locked.
>> 
>> The backchannel uses the new dynamic slot allocator, even though we only
>> currently support a single back channel slot.
>> 
>> Signed-off-by: Andy Adamson <andros@xxxxxxxxxx>
>> ---
>> fs/nfs/callback_proc.c    |   25 +++-
>> fs/nfs/internal.h         |    2 +
>> fs/nfs/nfs4_fs.h          |    1 +
>> fs/nfs/nfs4proc.c         |  297 ++++++++++++++++++++++++++++++++++-----------
>> fs/nfs/nfs4state.c        |   12 +--
>> fs/nfs/nfs4xdr.c          |   20 ++--
>> include/linux/nfs_fs_sb.h |   12 +-
>> include/linux/nfs_xdr.h   |    4 +-
>> 8 files changed, 266 insertions(+), 107 deletions(-)
>> 
>> diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c
>> index 54cea8a..77cc96c 100644
>> --- a/fs/nfs/callback_proc.c
>> +++ b/fs/nfs/callback_proc.c
>> @@ -342,7 +342,7 @@ validate_seqid(struct nfs4_slot_table *tbl, struct cb_sequenceargs * args)
>> 	if (args->csa_slotid >= NFS41_BC_MAX_CALLBACKS)
>> 		return htonl(NFS4ERR_BADSLOT);
>> 
>> -	slot = tbl->slots + args->csa_slotid;
>> +	slot = nfs4_lookup_slot_locked(tbl, args->csa_slotid);
>> 	dprintk("%s slot table seqid: %d\n", __func__, slot->seq_nr);
>> 
>> 	/* Normal */
>> @@ -377,6 +377,22 @@ out_ok:
>> 	return htonl(NFS4_OK);
>> }
>> 
>> +static bool test_slot_referring(struct nfs4_slot_table *tbl,
>> +				struct referring_call *ref)
>> +{
>> +	struct nfs4_slot *slot;
>> +	bool status = false;
>> +
>> +	spin_lock(&tbl->slot_tbl_lock);
>> +	if (test_bit(ref->rc_slotid, tbl->used_slots)) {
>> +		slot = nfs4_lookup_slot_locked(tbl, ref->rc_slotid);
>> +		if (slot->seq_nr == ref->rc_sequenceid)
>> +			status = true;
>> +	}
>> +	spin_unlock(&tbl->slot_tbl_lock);
>> +	return status;
>> +}
>> +
>> /*
>>  * For each referring call triple, check the session's slot table for
>>  * a match.  If the slot is in use and the sequence numbers match, the
>> @@ -417,12 +433,7 @@ static bool referring_call_exists(struct nfs_client *clp,
>> 				((u32 *)&rclist->rcl_sessionid.data)[2],
>> 				((u32 *)&rclist->rcl_sessionid.data)[3],
>> 				ref->rc_sequenceid, ref->rc_slotid);
>> -
>> -			spin_lock(&tbl->slot_tbl_lock);
>> -			status = (test_bit(ref->rc_slotid, tbl->used_slots) &&
>> -				  tbl->slots[ref->rc_slotid].seq_nr ==
>> -					ref->rc_sequenceid);
>> -			spin_unlock(&tbl->slot_tbl_lock);
>> +			status = test_slot_referring(tbl, ref);
>> 			if (status)
>> 				goto out;
>> 		}
>> diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
>> index c1a1bd8..4451abf 100644
>> --- a/fs/nfs/internal.h
>> +++ b/fs/nfs/internal.h
>> @@ -354,6 +354,8 @@ extern int _nfs4_call_sync_session(struct rpc_clnt *clnt,
>> 				   struct nfs4_sequence_args *args,
>> 				   struct nfs4_sequence_res *res,
>> 				   int cache_reply);
>> +struct nfs4_slot *nfs4_lookup_slot_locked(struct nfs4_slot_table *tbl,
>> +					  u8 slotid);
>> 
>> /*
>>  * Determine the device name as a string
>> diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
>> index 693ae22..ff87169 100644
>> --- a/fs/nfs/nfs4_fs.h
>> +++ b/fs/nfs/nfs4_fs.h
>> @@ -242,6 +242,7 @@ extern struct nfs4_session *nfs4_alloc_session(struct nfs_client *clp);
>> extern int nfs4_proc_create_session(struct nfs_client *);
>> extern int nfs4_proc_destroy_session(struct nfs4_session *);
>> extern int nfs4_init_session(struct nfs_server *server);
>> +extern void nfs4_reduce_slots_locked(struct nfs4_slot_table *tbl);
>> extern int nfs4_proc_get_lease_time(struct nfs_client *clp,
>> 		struct nfs_fsinfo *fsinfo);
>> extern int nfs4_proc_layoutcommit(struct nfs4_layoutcommit_data *data,
>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>> index 2638291..e3a7663 100644
>> --- a/fs/nfs/nfs4proc.c
>> +++ b/fs/nfs/nfs4proc.c
>> @@ -346,6 +346,162 @@ static void renew_lease(const struct nfs_server *server, unsigned long timestamp
>> #if defined(CONFIG_NFS_V4_1)
>> 
>> /*
>> + * Session dynamic slot table helper functions
>> + */
>> +
>> +static inline u32 slot_tbl_hash(const u8 slotid)
> 
> nit: "const" not really needed here...
> 
>> +{
>> +	return (u32)slotid % SLOT_TABLE_SIZE;
>> +}
>> +
>> +static void nfs4_init_slot(struct nfs4_slot *new, u8 slotid, int ivalue)
>> +{
>> +	INIT_HLIST_NODE(&new->slot_node);
>> +	new->slotid = slotid;
>> +	new->seq_nr = ivalue;
>> +}
>> +
>> +static void nfs4_insert_slot_locked(struct nfs4_slot_table *tbl,
>> +				    struct nfs4_slot *new)
>> +{
>> +	u32 hash = slot_tbl_hash(new->slotid);
>> +
>> +	hlist_add_head(&new->slot_node, &tbl->slots[hash]);
>> +	tbl->allocated_slots++;
>> +}
>> +
>> +/*
>> + * Allocate a slot for the next slotid (tbl->allocated_slotid)
>> + */
>> +static int nfs4_alloc_add_slot(struct nfs4_slot_table *tbl,
>> +			       int ivalue, int slotid,
>> +			       gfp_t gfp_flags)
>> +{
>> +	struct nfs4_slot *new;
>> +	struct rpc_task *task;
>> +
>> +	dprintk("--> %s slotid=%u tbl->allocated_slots=%d\n", __func__,
>> +		slotid, tbl->allocated_slots);
>> +	new = kzalloc(sizeof(struct nfs4_slot), gfp_flags);
>> +	if (!new)
>> +		return -ENOMEM;
>> +	/* tbl->allocated_slots holds the next unallocated slotid */
>> +	nfs4_init_slot(new, slotid, ivalue);
>> +	spin_lock(&tbl->slot_tbl_lock);
>> +	if (tbl->allocated_slots != slotid) {
> 
> This condition doesn't seem to be reliable.
> What if the slot table shrunk?
> 
>> +		spin_unlock(&tbl->slot_tbl_lock);
>> +		kfree(new);
>> +		dprintk("%s slotid %u already allocated\n", __func__,
>> +			slotid);
>> +		return 0;
>> +	}
>> +	nfs4_insert_slot_locked(tbl, new);
>> +
>> +	/* This only applies to dynamic allocation */
>> +	task = rpc_wake_up_next(&tbl->slot_tbl_waitq);
>> +	if (task)
>> +		dprintk("%s woke up task %5u\n", __func__, task->tk_pid);
>> +	spin_unlock(&tbl->slot_tbl_lock);
>> +	return 0;
>> +}
>> +
>> +/*
>> + * Allocate the minimal number of slots required by the transport.
>> + * Called at session creation.
>> + */
>> +static int nfs4_prealloc_slots(struct nfs4_slot_table *tbl, int num, int ivalue)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; i < num; i++) {
>> +		if (nfs4_alloc_add_slot(tbl, ivalue, tbl->allocated_slots,
>> +					GFP_NOFS) != 0)
>> +			return -ENOMEM;
> 
> Returning nfs4_alloc_add_slot's status would be more appropriate.
> How about also freeing 0 to i-1 in the error case?
> 
>> +	}
>> +	return 0;
>> +}
>> +
>> +/*
>> + * Allocate the next slotid. If allocation fails, next request will retry.
>> + */
>> +static void nfs4_dynamic_alloc_slot(struct nfs4_slot_table *tbl, u8 slotid)
>> +{
>> +	if (slotid != tbl->allocated_slots) {
>> +		dprintk("%s slotid %u already allocated\n", __func__, slotid);
>> +		return;
>> +	}
> 
> This is checked again under the lock in nfs4_alloc_add_slot, no?
> so if it is not supposed to be a common case (which I don't believe
> it is) I'd just forget about this optimization and call the latter
> directly.
> 
>> +	nfs4_alloc_add_slot(tbl, 1, slotid, GFP_NOWAIT);
>> +}
>> +
>> +/*
>> + * Return the slot associated with the slotid returned by nfs4_find_slot.
>> + * If the slot is not found, it has not been allocated.
>> + */
>> +struct nfs4_slot *
>> +nfs4_lookup_slot_locked(struct nfs4_slot_table *tbl, u8 slotid)
>> +{
>> +	struct nfs4_slot *sp;
>> +	struct hlist_node *n;
>> +	u32 hash = slot_tbl_hash(slotid);
>> +
>> +	hlist_for_each_entry(sp, n, &tbl->slots[hash], slot_node) {
>> +		if (sp->slotid == slotid)
>> +			return sp;
>> +	}
>> +	return NULL;
>> +}
>> +
>> +static void nfs4_remove_slot_locked(struct nfs4_slot_table *tbl,
>> +				    struct nfs4_slot *slot)
>> +{
>> +	dprintk("--> %s slotid %d\n", __func__, slot->slotid);
>> +	hlist_del_init(&slot->slot_node);
>> +	tbl->allocated_slots--;
>> +	kfree(slot);
>> +}
>> +
>> +static void nfs4_free_all_slots(struct nfs4_slot_table *tbl)
>> +{
>> +	struct nfs4_slot *slotp;
>> +	int i;
>> +
>> +	spin_lock(&tbl->slot_tbl_lock);
>> +	for (i = 0; i < SLOT_TABLE_SIZE; i++) {
>> +		while (!hlist_empty(&tbl->slots[i])) {
>> +			slotp = hlist_entry(tbl->slots[i].first,
>> +					    struct nfs4_slot, slot_node);
>> +			nfs4_remove_slot_locked(tbl, slotp);
>> +		}
>> +		/* re-initialize hlist_head */
>> +		tbl->slots[i].first = NULL;
>> +	}
>> +	spin_unlock(&tbl->slot_tbl_lock);
>> +}
>> +
>> +/*
>> + * Remove num_dec number of contiguous slotids starting from highest
>> + * allocated slotid
>> + *
>> + * Note: set the new tbl->max_slots prior to calling.
>> + */
>> +void nfs4_reduce_slots_locked(struct nfs4_slot_table *tbl)
>> +{
>> +	struct nfs4_slot *removeme;
>> +	int i, rm_slotid = tbl->allocated_slots - 1;
>> +	int num_dec = tbl->allocated_slots - tbl->max_slots;
>> +
>> +	/* Reset of the slot table can make num_dec <= 0 */
>> +	if (num_dec <= 0)
>> +		return;
>> +	for (i = 0; i < num_dec; i++) {
>> +		removeme = nfs4_lookup_slot_locked(tbl, rm_slotid);
>> +		BUG_ON(removeme == NULL);
>> +		nfs4_remove_slot_locked(tbl, removeme);
>> +		rm_slotid--;
>> +	}
>> +}
>> +
>> +/*
>>  * nfs4_free_slot - free a slot and efficiently update slot table.
>>  *
>>  * freeing a slot is trivially done by clearing its respective bit
>> @@ -390,8 +546,11 @@ static void nfs4_check_drain_fc_complete(struct nfs4_session *ses)
>> 
>> 	if (!test_bit(NFS4_SESSION_DRAINING, &ses->session_state)) {
>> 		task = rpc_wake_up_next(&ses->fc_slot_table.slot_tbl_waitq);
>> -		if (task)
>> +		if (task) {
>> 			rpc_task_set_priority(task, RPC_PRIORITY_PRIVILEGED);
>> +			dprintk("%s woke up task pid %5u\n", __func__,
>> +				task->tk_pid);
>> +		}
>> 		return;
>> 	}
>> 
>> @@ -427,7 +586,7 @@ static void nfs41_sequence_free_slot(struct nfs4_sequence_res *res)
>> 	}
>> 
>> 	spin_lock(&tbl->slot_tbl_lock);
>> -	nfs4_free_slot(tbl, res->sr_slot - tbl->slots);
>> +	nfs4_free_slot(tbl, res->sr_slot->slotid);
>> 	nfs4_check_drain_fc_complete(res->sr_session);
>> 	spin_unlock(&tbl->slot_tbl_lock);
>> 	res->sr_slot = NULL;
>> @@ -468,10 +627,8 @@ static int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *
>> 		 * returned NFS4ERR_DELAY as per Section 2.10.6.2
>> 		 * of RFC5661.
>> 		 */
>> -		dprintk("%s: slot=%td seq=%d: Operation in progress\n",
>> -			__func__,
>> -			res->sr_slot - res->sr_session->fc_slot_table.slots,
>> -			res->sr_slot->seq_nr);
>> +		dprintk("%s: slotid=%u seq=%d: Operation in progress\n",
>> +			__func__, res->sr_slot->slotid, res->sr_slot->seq_nr);
>> 		goto out_retry;
>> 	default:
>> 		/* Just update the slot sequence no. */
>> @@ -479,7 +636,8 @@ static int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *
>> 	}
>> out:
>> 	/* The session may be reset by one of the error handlers. */
>> -	dprintk("%s: Error %d free the slot \n", __func__, res->sr_status);
>> +	dprintk("%s: Error %d free the slot for task pid %5u\n", __func__,
>> +		res->sr_status, task->tk_pid);
>> 	nfs41_sequence_free_slot(res);
>> 	return 1;
>> out_retry:
>> @@ -540,7 +698,7 @@ int nfs41_setup_sequence(struct nfs4_session *session,
>> 	struct nfs4_slot_table *tbl;
>> 	u8 slotid;
>> 
>> -	dprintk("--> %s\n", __func__);
>> +	dprintk("--> %s task pid %5u\n", __func__, task->tk_pid);
>> 	/* slot already allocated? */
>> 	if (res->sr_slot != NULL)
>> 		return 0;
>> @@ -575,12 +733,24 @@ int nfs41_setup_sequence(struct nfs4_session *session,
>> 		dprintk("<-- %s: no free slots\n", __func__);
>> 		return -EAGAIN;
>> 	}
>> +	slot = nfs4_lookup_slot_locked(tbl, slotid);
>> +	if (slot == NULL) {
>> +		/* keep FIFO order */
>> +		rpc_task_set_priority(task, RPC_PRIORITY_PRIVILEGED);
>> +		rpc_sleep_on(&tbl->slot_tbl_waitq, task, NULL);
>> +		nfs4_free_slot(tbl, slotid);
> 
> why free the slot here?
> 
> Benny
> 
>> +		spin_unlock(&tbl->slot_tbl_lock);
>> +		dprintk("%s task pid %5u sleeping for dynamic slot %d\n",
>> +			__func__, task->tk_pid, slotid);
>> +		/* rpc_wakeup_next called upon success by slot allocator */
>> +		nfs4_dynamic_alloc_slot(tbl, slotid);
>> +		return -EAGAIN;
>> +	}
>> 	spin_unlock(&tbl->slot_tbl_lock);
>> 
>> 	rpc_task_set_priority(task, RPC_PRIORITY_NORMAL);
>> -	slot = tbl->slots + slotid;
>> 	args->sa_session = session;
>> -	args->sa_slotid = slotid;
>> +	args->sa_slot = slot;
>> 	args->sa_cache_this = cache_reply;
>> 
>> 	dprintk("<-- %s slotid=%d seqid=%d\n", __func__, slotid, slot->seq_nr);
>> @@ -613,9 +783,9 @@ int nfs4_setup_sequence(const struct nfs_server *server,
>> 		goto out;
>> 	}
>> 
>> -	dprintk("--> %s clp %p session %p sr_slot %td\n",
>> +	dprintk("--> %s clp %p session %p sr_slotid %d\n",
>> 		__func__, session->clp, session, res->sr_slot ?
>> -			res->sr_slot - session->fc_slot_table.slots : -1);
>> +			res->sr_slot->slotid : -1);
>> 
>> 	ret = nfs41_setup_sequence(session, args, res, cache_reply,
>> 				   task);
>> @@ -4976,84 +5146,64 @@ int nfs4_proc_get_lease_time(struct nfs_client *clp, struct nfs_fsinfo *fsinfo)
>> }
>> 
>> /*
>> - * Reset a slot table
>> + * Reset a slot table. Session has been drained and reset with new slot table
>> + * parameters from create_session.
>> + * Keep all allocated slots that fit into new slot table max_reqs parameter.
>>  */
>> -static int nfs4_reset_slot_table(struct nfs4_slot_table *tbl, u32 max_reqs,
>> +static void nfs4_reset_slot_table(struct nfs4_slot_table *tbl, u32 new_max_reqs,
>> 				 int ivalue)
>> {
>> -	struct nfs4_slot *new = NULL;
>> +	struct nfs4_slot *sp;
>> +	struct hlist_node *n;
>> 	int i;
>> -	int ret = 0;
>> -
>> -	dprintk("--> %s: max_reqs=%u, tbl->max_slots %d\n", __func__,
>> -		max_reqs, tbl->max_slots);
>> 
>> -	/* Does the newly negotiated max_reqs match the existing slot table? */
>> -	if (max_reqs != tbl->max_slots) {
>> -		ret = -ENOMEM;
>> -		new = kmalloc(max_reqs * sizeof(struct nfs4_slot),
>> -			      GFP_NOFS);
>> -		if (!new)
>> -			goto out;
>> -		ret = 0;
>> -		kfree(tbl->slots);
>> -	}
>> 	spin_lock(&tbl->slot_tbl_lock);
>> -	if (new) {
>> -		tbl->slots = new;
>> -		tbl->max_slots = max_reqs;
>> +	tbl->max_slots = new_max_reqs;
>> +	nfs4_reduce_slots_locked(tbl);
>> +	tbl->highest_used_slotid = -1;
>> +
>> +	for (i = 0; i < SLOT_TABLE_SIZE; i++) {
>> +		hlist_for_each_entry(sp, n, &tbl->slots[i], slot_node)
>> +			sp->seq_nr = ivalue;
>> 	}
>> -	for (i = 0; i < tbl->max_slots; ++i)
>> -		tbl->slots[i].seq_nr = ivalue;
>> 	spin_unlock(&tbl->slot_tbl_lock);
>> -	dprintk("%s: tbl=%p slots=%p max_slots=%d\n", __func__,
>> -		tbl, tbl->slots, tbl->max_slots);
>> -out:
>> -	dprintk("<-- %s: return %d\n", __func__, ret);
>> -	return ret;
>> +	dprintk("%s: tbl->max_slots=%d tbl->allocated_slots=%d\n",
>> +		__func__, tbl->max_slots, tbl->allocated_slots);
>> +	return;
>> }
>> 
>> /* Destroy the slot table */
>> static void nfs4_destroy_slot_tables(struct nfs4_session *session)
>> {
>> -	if (session->fc_slot_table.slots != NULL) {
>> -		kfree(session->fc_slot_table.slots);
>> -		session->fc_slot_table.slots = NULL;
>> -	}
>> -	if (session->bc_slot_table.slots != NULL) {
>> -		kfree(session->bc_slot_table.slots);
>> -		session->bc_slot_table.slots = NULL;
>> -	}
>> -	return;
>> +	dprintk("--> %s\n", __func__);
>> +
>> +	nfs4_free_all_slots(&session->fc_slot_table);
>> +	nfs4_free_all_slots(&session->bc_slot_table);
>> }
>> 
>> /*
>>  * Initialize slot table
>>  */
>> static int nfs4_init_slot_table(struct nfs4_slot_table *tbl,
>> -		int max_slots, int ivalue)
>> +		int max_slots, int num_prealloc, int ivalue)
>> {
>> -	struct nfs4_slot *slot;
>> -	int ret = -ENOMEM;
>> +	int ret;
>> 
>> 	BUG_ON(max_slots > NFS4_MAX_SLOT_TABLE);
>> -
>> -	dprintk("--> %s: max_reqs=%u\n", __func__, max_slots);
>> -
>> -	slot = kcalloc(max_slots, sizeof(struct nfs4_slot), GFP_NOFS);
>> -	if (!slot)
>> +	ret = nfs4_prealloc_slots(tbl, num_prealloc, ivalue);
>> +	if (ret) {
>> +		nfs4_free_all_slots(tbl);
>> 		goto out;
>> +	}
>> 	ret = 0;
>> 
>> 	spin_lock(&tbl->slot_tbl_lock);
>> 	tbl->max_slots = max_slots;
>> -	tbl->slots = slot;
>> 	tbl->highest_used_slotid = -1;  /* no slot is currently used */
>> 	spin_unlock(&tbl->slot_tbl_lock);
>> -	dprintk("%s: tbl=%p slots=%p max_slots=%d\n", __func__,
>> -		tbl, tbl->slots, tbl->max_slots);
>> +	dprintk("%s: tbl=%p max_slots=%d, tbl->allocated_slots=%d\n", __func__,
>> +		tbl, tbl->max_slots, tbl->allocated_slots);
>> out:
>> -	dprintk("<-- %s: return %d\n", __func__, ret);
>> 	return ret;
>> }
>> 
>> @@ -5063,30 +5213,34 @@ out:
>> static int nfs4_setup_session_slot_tables(struct nfs4_session *ses)
>> {
>> 	struct nfs4_slot_table *tbl;
>> -	int status;
>> +	int status = 0;
>> 
>> 	dprintk("--> %s\n", __func__);
>> 	/* Fore channel */
>> 	tbl = &ses->fc_slot_table;
>> -	if (tbl->slots == NULL) {
>> -		status = nfs4_init_slot_table(tbl, ses->fc_attrs.max_reqs, 1);
>> +	if (tbl->allocated_slots == 0) {
>> +		status = nfs4_init_slot_table(tbl, ses->fc_attrs.max_reqs,
>> +				ses->clp->cl_rpcclient->cl_xprt->min_reqs, 1);
>> 		if (status) /* -ENOMEM */
>> 			return status;
>> 	} else {
>> -		status = nfs4_reset_slot_table(tbl, ses->fc_attrs.max_reqs, 1);
>> -		if (status)
>> -			return status;
>> +		nfs4_reset_slot_table(tbl, ses->fc_attrs.max_reqs, 1);
>> 	}
>> +
>> 	/* Back channel */
>> 	tbl = &ses->bc_slot_table;
>> -	if (tbl->slots == NULL) {
>> -		status = nfs4_init_slot_table(tbl, ses->bc_attrs.max_reqs, 0);
>> +	if (tbl->allocated_slots == 0) {
>> +		status = nfs4_init_slot_table(tbl, ses->bc_attrs.max_reqs,
>> +				/* Backchannel max_reqs == 1 */
>> +				ses->bc_attrs.max_reqs, 0);
>> 		if (status)
>> 			/* Fore and back channel share a connection so get
>> 			 * both slot tables or neither */
>> 			nfs4_destroy_slot_tables(ses);
>> -	} else
>> -		status = nfs4_reset_slot_table(tbl, ses->bc_attrs.max_reqs, 0);
>> +	} else {
>> +		nfs4_reset_slot_table(tbl, ses->bc_attrs.max_reqs, 0);
>> +	}
>> +
>> 	return status;
>> }
>> 
>> @@ -5276,7 +5430,6 @@ int nfs4_proc_create_session(struct nfs_client *clp)
>> 
>> 	/* Init or reset the session slot tables */
>> 	status = nfs4_setup_session_slot_tables(session);
>> -	dprintk("slot table setup returned %d\n", status);
>> 	if (status)
>> 		goto out;
>> 
>> @@ -5284,7 +5437,7 @@ int nfs4_proc_create_session(struct nfs_client *clp)
>> 	dprintk("%s client>seqid %d sessionid %u:%u:%u:%u\n", __func__,
>> 		clp->cl_seqid, ptr[0], ptr[1], ptr[2], ptr[3]);
>> out:
>> -	dprintk("<-- %s\n", __func__);
>> +	dprintk("<-- %s status %d\n", __func__, status);
>> 	return status;
>> }
>> 
>> diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
>> index 39914be..8260865 100644
>> --- a/fs/nfs/nfs4state.c
>> +++ b/fs/nfs/nfs4state.c
>> @@ -1573,26 +1573,16 @@ static int nfs4_recall_slot(struct nfs_client *clp)
>> {
>> 	struct nfs4_slot_table *fc_tbl = &clp->cl_session->fc_slot_table;
>> 	struct nfs4_channel_attrs *fc_attrs = &clp->cl_session->fc_attrs;
>> -	struct nfs4_slot *new, *old;
>> -	int i;
>> 
>> 	nfs4_begin_drain_session(clp);
>> -	new = kmalloc(fc_tbl->target_max_slots * sizeof(struct nfs4_slot),
>> -		      GFP_NOFS);
>> -        if (!new)
>> -		return -ENOMEM;
>> 
>> 	spin_lock(&fc_tbl->slot_tbl_lock);
>> -	for (i = 0; i < fc_tbl->target_max_slots; i++)
>> -		new[i].seq_nr = fc_tbl->slots[i].seq_nr;
>> -	old = fc_tbl->slots;
>> -	fc_tbl->slots = new;
>> 	fc_tbl->max_slots = fc_tbl->target_max_slots;
>> +	nfs4_reduce_slots_locked(fc_tbl);
>> 	fc_tbl->target_max_slots = 0;
>> 	fc_attrs->max_reqs = fc_tbl->max_slots;
>> 	spin_unlock(&fc_tbl->slot_tbl_lock);
>> 
>> -	kfree(old);
>> 	nfs4_end_drain_session(clp);
>> 	return 0;
>> }
>> diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
>> index e6161b2..c42ec29 100644
>> --- a/fs/nfs/nfs4xdr.c
>> +++ b/fs/nfs/nfs4xdr.c
>> @@ -1872,7 +1872,6 @@ static void encode_sequence(struct xdr_stream *xdr,
>> #if defined(CONFIG_NFS_V4_1)
>> 	struct nfs4_session *session = args->sa_session;
>> 	struct nfs4_slot_table *tp;
>> -	struct nfs4_slot *slot;
>> 	__be32 *p;
>> 
>> 	if (!session)
>> @@ -1880,8 +1879,7 @@ static void encode_sequence(struct xdr_stream *xdr,
>> 
>> 	tp = &session->fc_slot_table;
>> 
>> -	WARN_ON(args->sa_slotid == NFS4_MAX_SLOT_TABLE);
>> -	slot = tp->slots + args->sa_slotid;
>> +	WARN_ON(args->sa_slot->slotid == NFS4_MAX_SLOT_TABLE);
>> 
>> 	p = reserve_space(xdr, 4 + NFS4_MAX_SESSIONID_LEN + 16);
>> 	*p++ = cpu_to_be32(OP_SEQUENCE);
>> @@ -1896,11 +1894,11 @@ static void encode_sequence(struct xdr_stream *xdr,
>> 		((u32 *)session->sess_id.data)[1],
>> 		((u32 *)session->sess_id.data)[2],
>> 		((u32 *)session->sess_id.data)[3],
>> -		slot->seq_nr, args->sa_slotid,
>> +		args->sa_slot->seq_nr, args->sa_slot->slotid,
>> 		tp->highest_used_slotid, args->sa_cache_this);
>> 	p = xdr_encode_opaque_fixed(p, session->sess_id.data, NFS4_MAX_SESSIONID_LEN);
>> -	*p++ = cpu_to_be32(slot->seq_nr);
>> -	*p++ = cpu_to_be32(args->sa_slotid);
>> +	*p++ = cpu_to_be32(args->sa_slot->seq_nr);
>> +	*p++ = cpu_to_be32(args->sa_slot->slotid);
>> 	*p++ = cpu_to_be32(tp->highest_used_slotid);
>> 	*p = cpu_to_be32(args->sa_cache_this);
>> 	hdr->nops++;
>> @@ -5361,13 +5359,17 @@ static int decode_sequence(struct xdr_stream *xdr,
>> 	/* seqid */
>> 	dummy = be32_to_cpup(p++);
>> 	if (dummy != res->sr_slot->seq_nr) {
>> -		dprintk("%s Invalid sequence number\n", __func__);
>> +		dprintk("%s Invalid seq num %d for [slotid:seq_nr] [%d:%d]\n",
>> +			__func__, dummy, res->sr_slot->slotid,
>> +			res->sr_slot->seq_nr);
>> 		goto out_err;
>> 	}
>> 	/* slot id */
>> 	dummy = be32_to_cpup(p++);
>> -	if (dummy != res->sr_slot - res->sr_session->fc_slot_table.slots) {
>> -		dprintk("%s Invalid slot id\n", __func__);
>> +	if (dummy != res->sr_slot->slotid) {
>> +		dprintk("%s Invalid slot id %d for [slotid:seq_nr] [%d:%d]\n",
>> +			__func__, dummy, res->sr_slot->slotid,
>> +			res->sr_slot->seq_nr);
>> 		goto out_err;
>> 	}
>> 	/* highest slot id - currently not processed */
>> diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
>> index b5479df..90c6e2b 100644
>> --- a/include/linux/nfs_fs_sb.h
>> +++ b/include/linux/nfs_fs_sb.h
>> @@ -193,12 +193,15 @@ struct nfs_server {
>> 
>> /* Sessions */
>> #define SLOT_TABLE_SZ (NFS4_MAX_SLOT_TABLE/(8*sizeof(long)))
>> +#define SLOT_TABLE_BITS                5
>> +#define SLOT_TABLE_SIZE                (1 << SLOT_TABLE_BITS)
>> struct nfs4_slot_table {
>> -	struct nfs4_slot *slots;		/* seqid per slot */
>> +	struct hlist_head slots[SLOT_TABLE_SIZE];
>> 	unsigned long   used_slots[SLOT_TABLE_SZ]; /* used/unused bitmap */
>> 	spinlock_t	slot_tbl_lock;
>> 	struct rpc_wait_queue	slot_tbl_waitq;	/* allocators may wait here */
>> -	int		max_slots;		/* # slots in table */
>> +	int		allocated_slots;	/* # slots in table */
>> +	int		max_slots;		/* max # slots in table */
>> 	int		highest_used_slotid;	/* sent to server on each SEQ.
>> 						 * op for dynamic resizing */
>> 	int		target_max_slots;	/* Set by CB_RECALL_SLOT as
>> @@ -206,11 +209,6 @@ struct nfs4_slot_table {
>> 	struct completion complete;
>> };
>> 
>> -static inline int slot_idx(struct nfs4_slot_table *tbl, struct nfs4_slot *sp)
>> -{
>> -	return sp - tbl->slots;
>> -}
>> -
>> /*
>>  * Session related parameters
>>  */
>> diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
>> index c74595b..76b27a4 100644
>> --- a/include/linux/nfs_xdr.h
>> +++ b/include/linux/nfs_xdr.h
>> @@ -168,12 +168,14 @@ struct nfs4_channel_attrs {
>> 
>> /* nfs41 sessions slot seqid */
>> struct nfs4_slot {
>> +	struct hlist_node	slot_node;
>> 	u32		 	seq_nr;
>> +	u8			slotid;
>> };
>> 
>> struct nfs4_sequence_args {
>> 	struct nfs4_session	*sa_session;
>> -	u8			sa_slotid;
>> +	struct nfs4_slot        *sa_slot;
>> 	u8			sa_cache_this;
>> };
>> 

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