From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 39EC3839E4; Tue, 29 Oct 2024 10:28:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730197715; cv=none; b=GnwP1tAAqcXtHNtB9kLy6Tye/ObqyEC6lBJJYsQ7QwGYVMGerRMWbAThxPZoiCrLFTEA8gYlMq8bIpZ3x0HtNU/wwtUrJK/ntg1p9Yk+RctHtqG7mPeF1wTruinuVLrFq8urovBRKooAXYiOgAQLJ8SR7wlbfQjzcGFUzvRQ51o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730197715; c=relaxed/simple; bh=QtYHIjyhmIhI945OulwDRbZKEnb/dQ6si5qiw+PKbik=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=s8PqQ/IjSV2MGadUlvGYQRC+oIZtTU1vvduB44kg0OUJcgk3BJwYVjKz7UOIRi/q9cjtMdFskAV8GcnhefgH4hwS45DHMRw8i/FRrtN+m5M4kLrAzONMCVxZSHwnARDad9X+T8YXM1jvDZwi/PIyMXKcF+1vWaQ2kGAnXHmWZyc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=adwV9O77; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="adwV9O77" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 25B80C4CEE5; Tue, 29 Oct 2024 10:28:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1730197714; bh=QtYHIjyhmIhI945OulwDRbZKEnb/dQ6si5qiw+PKbik=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=adwV9O77rGjm5DjFdblIZ89SgFMYi90LRVvnVLKJjQ1mKeJTeq8D5bhGimCr5jJCt jx9048c2UoG58v6MwkUXGBghP1/fP9t5gexWdoUQYP6i62FiDA1rVyrEympIv1e/Jp MQNNCoXf1yPbtKsXkE0DtSZQtvebTV/bHg0vBYKmxnU/4a4BFL4Xx27Uxs2Say2b0D a2dp0klIc6mHZrrvqjA3zDVmn3JnS5xcPVSnZUy15rmJU9mrX6BA2CMhCHnCh1LbxU NPxW8ZtWss2R7nRCnbfmXzFlUxGQqY12X0hrvktTsR+lxxtH+UB4cWWSvTSEalte54 x/htNmw3MJxrA== Message-ID: Subject: Re: [PATCH 2/2] nfsd: allow for more callback session slots From: Jeff Layton To: Chuck Lever Cc: Neil Brown , Dai Ngo , Tom Talpey , Olga Kornievskaia , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 29 Oct 2024 06:28:32 -0400 In-Reply-To: References: <20241028-bcwide-v1-0-0e75a8219dc0@kernel.org> <20241028-bcwide-v1-2-0e75a8219dc0@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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the callback channel, which i= s > > 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). > >=20 > > 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. While they are part of the > > session, the fields are protected by the cl_lock. > >=20 > > Fix nfsd41_cb_get_slot to always search for the lowest slotid (using > > ffs()), and change it to continually retry until there is a slot > > available. > >=20 > > 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. > >=20 > > Signed-off-by: Jeff Layton > > --- > > fs/nfsd/nfs4callback.c | 107 +++++++++++++++++++++++++++++++++++------= -------- > > fs/nfsd/nfs4state.c | 7 +++- > > fs/nfsd/state.h | 12 +++--- > > fs/nfsd/trace.h | 2 +- > > 4 files changed, 89 insertions(+), 39 deletions(-) > >=20 > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > > index e38fa834b3d91333acf1425eb14c644e5d5f2601..64b85b164125b244494f980= 5840a0d8a1ccb4c1b 100644 > > --- a/fs/nfsd/nfs4callback.c > > +++ b/fs/nfsd/nfs4callback.c > > @@ -406,6 +406,16 @@ encode_cb_getattr4args(struct xdr_stream *xdr, str= uct nfs4_cb_compound_hdr *hdr, > > hdr->nops++; > > } > > =20 > > +static u32 highest_unset_index(u32 word) > > +{ > > + int i; > > + > > + for (i =3D sizeof(word) * 8 - 1; i > 0; --i) > > + if (!(word & BIT(i))) > > + return i; > > + return 0; > > +} > > + >=20 > Isn't this the same as ffz() or "ffs(~(x))" ? >=20 No. I need the _last_ cleared bit in the word. It looks though like there is a fls() function that might be usable, so I could maybe do fls(~(x)). I'll experiment with that. >=20 > > /* > > * CB_SEQUENCE4args > > * > > @@ -432,15 +442,38 @@ static void encode_cb_sequence4args(struct xdr_st= ream *xdr, > > encode_sessionid4(xdr, session); > > =20 > > p =3D xdr_reserve_space(xdr, 4 + 4 + 4 + 4 + 4); > > - *p++ =3D cpu_to_be32(session->se_cb_seq_nr); /* csa_sequenceid */ > > - *p++ =3D xdr_zero; /* csa_slotid */ > > - *p++ =3D xdr_zero; /* csa_highest_slotid */ > > + *p++ =3D cpu_to_be32(session->se_cb_seq_nr[cb->cb_held_slot]); /* csa= _sequenceid */ > > + *p++ =3D cpu_to_be32(cb->cb_held_slot); /* csa_slotid */ > > + *p++ =3D cpu_to_be32(max(highest_unset_index(session->se_cb_slot_avai= l), > > + session->se_cb_highest_slot)); /* csa_highest_slotid */ >=20 > This encoder doesn't hold the client's cl_lock, but does reference > fields that are updated while that lock is held. >=20 > Also, should a per-session spin lock be used instead of cl_lock? >=20 > Is locking even necessary? All of these calls are prepared in a > single-threaded workqueue. Reply processing can only free slots, so > it doesn't need to exclude session slot selection. >=20 NFSv4 callbacks use async RPCs. The encoding and transmit is done in the context of the (single-threaded) workqueue, but the reply is handled by rpciod. Since we release the slot after the reply in rpciod context, I think we do require locking here. I also worry a bit that relying on the single-threaded workqueue may end up being a bottleneck at some point in the future, so I see having clear locking here as a benefit. I'm open to switching to a per-session lock of some sort, but I don't see a real need here. Only one session will be used as the backchannel at a time, so there shouldn't be competing access between different sessions for the cl_lock. We are competing with the other uses of the cl_lock, but this one should be pretty quick. My preference would be to add extra locking only once it becomes clear that it's necessary. >=20 > > *p++ =3D xdr_zero; /* csa_cachethis */ > > xdr_encode_empty_array(p); /* csa_referring_call_lists */ > > =20 > > hdr->nops++; > > } > > =20 > > +static void update_cb_slot_table(struct nfsd4_session *ses, u32 highes= t) >=20 > Nit: Can you use the name "target" instead of "highest" ? >=20 Will do. >=20 > > +{ > > + /* No need to do anything if nothing changed */ > > + if (likely(highest =3D=3D READ_ONCE(ses->se_cb_highest_slot))) > > + return; > > + > > + spin_lock(&ses->se_client->cl_lock); > > + /* If growing the slot table, reset any new sequences to 1 */ > > + if (highest > ses->se_cb_highest_slot) { > > + int i; > > + > > + for (i =3D ses->se_cb_highest_slot; i <=3D highest; ++i) { > > + /* beyond the end of the array? */ > > + if (i >=3D NFSD_BC_SLOT_TABLE_MAX) > > + break; >=20 > Nit: why not cap "highest" at NFSD_BC_SLOT_TABLE_MAX before starting > this for loop? >=20 Duh -- of course. Will fix. >=20 > > + ses->se_cb_seq_nr[i] =3D 1; > > + } > > + } > > + ses->se_cb_highest_slot =3D highest; > > + spin_unlock(&ses->se_client->cl_lock); > > +} > > + > > /* > > * CB_SEQUENCE4resok > > * > > @@ -485,7 +518,7 @@ static int decode_cb_sequence4resok(struct xdr_stre= am *xdr, > > p +=3D XDR_QUADLEN(NFS4_MAX_SESSIONID_LEN); > > =20 > > dummy =3D be32_to_cpup(p++); > > - if (dummy !=3D session->se_cb_seq_nr) { > > + if (dummy !=3D session->se_cb_seq_nr[cb->cb_held_slot]) { >=20 > Nit: Let's rename "dummy" as "seqid", and add a "highest" variable > for the next XDR field (not shown here). >=20 Ok. >=20 > > dprintk("NFS: %s Invalid sequence number\n", __func__); > > goto out; > > } > > @@ -496,9 +529,15 @@ static int decode_cb_sequence4resok(struct xdr_str= eam *xdr, > > goto out; > > } > > =20 > > - /* > > - * FIXME: process highest slotid and target highest slotid > > - */ > > + p++; // ignore current highest slot value > > + > > + dummy =3D be32_to_cpup(p++); >=20 > Nit: I prefer a name for this argument variable like "target". >=20 > The compiler should be able to combine the usage of these variables > into a single memory location. >=20 Ok. >=20 > > + if (dummy =3D=3D 0) { > > + dprintk("NFS: %s Invalid target highest slotid\n", __func__); > > + goto out; > > + } > > + > > + update_cb_slot_table(session, dummy); > > status =3D 0; > > out: > > cb->cb_seq_status =3D status; > > @@ -1208,31 +1247,38 @@ void nfsd4_change_callback(struct nfs4_client *= clp, struct nfs4_cb_conn *conn) > > * If the slot is available, then mark it busy. Otherwise, set the > > * thread for sleeping on the callback RPC wait queue. > > */ > > -static bool nfsd41_cb_get_slot(struct nfsd4_callback *cb, struct rpc_t= ask *task) > > +static void nfsd41_cb_get_slot(struct nfsd4_callback *cb, struct rpc_t= ask *task) > > { > > struct nfs4_client *clp =3D cb->cb_clp; > > + struct nfsd4_session *ses =3D clp->cl_cb_session; > > + int idx; > > =20 > > - if (!cb->cb_holds_slot && > > - test_and_set_bit(0, &clp->cl_cb_slot_busy) !=3D 0) { > > + if (cb->cb_held_slot >=3D 0) > > + return; > > +retry: > > + spin_lock(&clp->cl_lock); > > + idx =3D ffs(ses->se_cb_slot_avail) - 1; > > + if (idx < 0 || idx > ses->se_cb_highest_slot) { > > + spin_unlock(&clp->cl_lock); > > rpc_sleep_on(&clp->cl_cb_waitq, task, NULL); > > - /* Race breaker */ > > - if (test_and_set_bit(0, &clp->cl_cb_slot_busy) !=3D 0) { > > - dprintk("%s slot is busy\n", __func__); > > - return false; > > - } > > - rpc_wake_up_queued_task(&clp->cl_cb_waitq, task); > > + goto retry; > > } > > - cb->cb_holds_slot =3D true; > > - return true; > > + /* clear the bit for the slot */ > > + ses->se_cb_slot_avail &=3D ~BIT(idx); > > + spin_unlock(&clp->cl_lock); > > + cb->cb_held_slot =3D idx; > > } > > =20 > > static void nfsd41_cb_release_slot(struct nfsd4_callback *cb) > > { > > struct nfs4_client *clp =3D cb->cb_clp; > > + struct nfsd4_session *ses =3D clp->cl_cb_session; > > =20 > > - if (cb->cb_holds_slot) { > > - cb->cb_holds_slot =3D false; > > - clear_bit(0, &clp->cl_cb_slot_busy); > > + if (cb->cb_held_slot >=3D 0) { > > + spin_lock(&clp->cl_lock); > > + ses->se_cb_slot_avail |=3D BIT(cb->cb_held_slot); > > + spin_unlock(&clp->cl_lock); > > + cb->cb_held_slot =3D -1; > > rpc_wake_up_next(&clp->cl_cb_waitq); > > } > > } > > @@ -1265,8 +1311,8 @@ static void nfsd4_cb_prepare(struct rpc_task *tas= k, void *calldata) >=20 > Nit: This patch should update the documenting comment before > nfsd4_cb_prepare() -- the patch implements "multiple slots". >=20 +1 >=20 > > trace_nfsd_cb_rpc_prepare(clp); > > cb->cb_seq_status =3D 1; > > cb->cb_status =3D 0; > > - if (minorversion && !nfsd41_cb_get_slot(cb, task)) > > - return; > > + if (minorversion) > > + nfsd41_cb_get_slot(cb, task); > > rpc_call_start(task); > > } > > =20 > > @@ -1292,7 +1338,7 @@ static bool nfsd4_cb_sequence_done(struct rpc_tas= k *task, struct nfsd4_callback > > return true; > > } > > =20 > > - if (!cb->cb_holds_slot) > > + if (cb->cb_held_slot < 0) > > goto need_restart; > > =20 > > /* This is the operation status code for CB_SEQUENCE */ > > @@ -1306,10 +1352,10 @@ static bool nfsd4_cb_sequence_done(struct rpc_t= ask *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 =3D false; > > break; > > @@ -1335,17 +1381,16 @@ static bool nfsd4_cb_sequence_done(struct rpc_t= ask *task, struct nfsd4_callback > > case -NFS4ERR_BADSLOT: > > goto retry_nowait; > > case -NFS4ERR_SEQ_MISORDERED: > > - if (session->se_cb_seq_nr !=3D 1) { > > - session->se_cb_seq_nr =3D 1; > > + if (session->se_cb_seq_nr[cb->cb_held_slot] !=3D 1) { > > + session->se_cb_seq_nr[cb->cb_held_slot] =3D 1; > > 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); > > =20 > > if (RPC_SIGNALLED(task)) > > goto need_restart; > > @@ -1565,7 +1610,7 @@ void nfsd4_init_cb(struct nfsd4_callback *cb, str= uct nfs4_client *clp, > > INIT_WORK(&cb->cb_work, nfsd4_run_cb_work); > > cb->cb_status =3D 0; > > cb->cb_need_restart =3D false; > > - cb->cb_holds_slot =3D false; > > + cb->cb_held_slot =3D -1; > > } > > =20 > > /** > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > > index 5b718b349396f1aecd0ad4c63b2f43342841bbd4..20a0d40202e40eed1c84d5d= 6c0a85b908804a6ba 100644 > > --- a/fs/nfsd/nfs4state.c > > +++ b/fs/nfsd/nfs4state.c > > @@ -2002,6 +2002,8 @@ static struct nfsd4_session *alloc_session(struct= nfsd4_channel_attrs *fattrs, > > } > > =20 > > memcpy(&new->se_fchannel, fattrs, sizeof(struct nfsd4_channel_attrs))= ; > > + new->se_cb_slot_avail =3D ~0U; > > + new->se_cb_highest_slot =3D battrs->maxreqs - 1; > > return new; > > out_free: > > while (i--) > > @@ -2132,7 +2134,9 @@ static void init_session(struct svc_rqst *rqstp, = struct nfsd4_session *new, stru > > =20 > > INIT_LIST_HEAD(&new->se_conns); > > =20 > > - new->se_cb_seq_nr =3D 1; > > + for (idx =3D 0; idx < NFSD_BC_SLOT_TABLE_MAX; ++idx) > > + new->se_cb_seq_nr[idx] =3D 1; > > + > > new->se_flags =3D cses->flags; > > new->se_cb_prog =3D cses->callback_prog; > > new->se_cb_sec =3D cses->cb_sec; > > @@ -3159,7 +3163,6 @@ static struct nfs4_client *create_client(struct x= dr_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 =3D 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 =3D NULL; > > diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h > > index 41cda86fea1f6166a0fd0215d3d458c93ced3e6a..2987c362bdd56251e736879= dc89302ada2259be8 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; > > }; > > =20 > > struct nfsd4_callback_ops { > > @@ -307,6 +307,9 @@ struct nfsd4_conn { > > unsigned char cn_flags; > > }; > > =20 > > +/* Max number of slots that the server will use in the backchannel */ > > +#define NFSD_BC_SLOT_TABLE_MAX 32 > > + >=20 > The new comment is unclear about whether this is an implementation > limit or a protocol limit. I suggest: >=20 > /* Maximum number of slots that NFSD implements for NFSv4.1+ backchannel = */ >=20 > And make this "sizeof(u32) * 8" or something similar that documents > where the value of this limit comes from. >=20 Ok. > > /* > > * Representation of a v4.1+ session. These are refcounted in a simila= r fashion > > * to the nfs4_client. References are only taken when the server is ac= tively > > @@ -325,7 +328,9 @@ struct nfsd4_session { > > struct nfsd4_cb_sec se_cb_sec; > > struct list_head se_conns; > > u32 se_cb_prog; > > - u32 se_cb_seq_nr; > > + u32 se_cb_slot_avail; /* bitmap of available slots */ > > + u32 se_cb_highest_slot; /* highest slot client wants */ > > + u32 se_cb_seq_nr[NFSD_BC_SLOT_TABLE_MAX]; > > struct nfsd4_slot *se_slots[]; /* forward channel slots */ > > }; > > =20 > > @@ -459,9 +464,6 @@ struct nfs4_client { > > */ > > struct dentry *cl_nfsd_info_dentry; > > =20 > > - /* 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..a9c17186b6892f1df8d7f7b= 90e250c2913ab23fe 100644 > > --- a/fs/nfsd/trace.h > > +++ b/fs/nfsd/trace.h > > @@ -1697,7 +1697,7 @@ TRACE_EVENT(nfsd_cb_free_slot, > > __entry->cl_id =3D sid->clientid.cl_id; > > __entry->seqno =3D sid->sequence; > > __entry->reserved =3D sid->reserved; > > - __entry->slot_seqno =3D session->se_cb_seq_nr; > > + __entry->slot_seqno =3D session->se_cb_seq_nr[cb->cb_held_slot]; > > ), > > TP_printk(SUNRPC_TRACE_TASK_SPECIFIER > > " sessionid=3D%08x:%08x:%08x:%08x new slot seqno=3D%u", > >=20 > > --=20 > > 2.47.0 > >=20 >=20 --=20 Jeff Layton