From: Trond Myklebust <trondmy@hammerspace.com>
To: "cuibixuan@linux.alibaba.com" <cuibixuan@linux.alibaba.com>,
"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Cc: "pete.wl@alibaba-inc.com" <pete.wl@alibaba-inc.com>,
"xiaoh.peixh@alibaba-inc.com" <xiaoh.peixh@alibaba-inc.com>,
"davem@davemloft.net" <davem@davemloft.net>,
"chuck.lever@oracle.com" <chuck.lever@oracle.com>,
"kuba@kernel.org" <kuba@kernel.org>,
"bfields@fieldses.org" <bfields@fieldses.org>,
"weipu.zy@alibaba-inc.com" <weipu.zy@alibaba-inc.com>,
"wenan.mwa@alibaba-inc.com" <wenan.mwa@alibaba-inc.com>,
"anna.schumaker@netapp.com" <anna.schumaker@netapp.com>
Subject: Re: [PATCH -next] SUNRPC: Clean XPRT_CONGESTED of xprt->state when rpc task is killed
Date: Wed, 22 Dec 2021 15:02:58 +0000 [thread overview]
Message-ID: <b8c236d99fd0f4e08dd0ee12a81274bd643a7690.camel@hammerspace.com> (raw)
In-Reply-To: <efbf73f3-c6cd-90f6-ef22-bde14be708cc@linux.alibaba.com>
On Wed, 2021-12-22 at 10:55 +0800, Bixuan Cui wrote:
>
> 在 2021/12/21 上午2:22, Trond Myklebust 写道:
>
> > On Mon, 2021-12-20 at 11:39 +0800, Bixuan Cui wrote:
> >
> > > ping~
> > >
> > > 在 2021/12/14 下午9:53, Bixuan Cui 写道:
> > >
> > > > When the values of tcp_max_slot_table_entries and
> > > > sunrpc.tcp_slot_table_entries are lower than the number of rpc
> > > > tasks,
> > > > xprt_dynamic_alloc_slot() in xprt_alloc_slot() will return -
> > > > EAGAIN,
> > > > and
> > > > then set xprt->state to XPRT_CONGESTED:
> > > > xprt_retry_reserve
> > > > ->xprt_do_reserve
> > > > ->xprt_alloc_slot
> > > > ->xprt_dynamic_alloc_slot // return -EAGAIN and task-
> > > >
> > > > > tk_rqstp is NULL
> > > > ->xprt_add_backlog // set_bit(XPRT_CONGESTED, &xprt-
> > > >
> > > > > state);
> > > > When rpc task is killed, XPRT_CONGESTED bit of xprt->state will
> > > > not
> > > > be
> > > > cleaned up and nfs hangs:
> > > > rpc_exit_task
> > > > ->xprt_release // if (req == NULL) is true, then
> > > > XPRT_CONGESTED
> > > > // bit not clean
> > > >
> > > > Add xprt_wake_up_backlog(xprt) to clean XPRT_CONGESTED bit in
> > > > xprt_release().
> > I'm not seeing how this explanation makes sense. If the task
> > doesn't
> > hold a slot, then freeing that task isn't going to clear the
> > congestion
> > caused by all the slots being in use.
> Hi,
> If the rpc task is free, call xprt_release() :
> void xprt_release(struct rpc_task *task)
> {
> if (req == NULL) {
> if (task->tk_client) {
> xprt = task->tk_xprt;
> xprt_release_write(xprt, task); // 1.
> release xprt
> }
> return;
> }
> ....
> if (likely(!bc_prealloc(req)))
> xprt->ops->free_slot(xprt, req); // 2. release slot
> and call xprt_wake_up_backlog(xprt, req) to wakeup next task(clear
> XPRT_CONGESTED bit if next is NULL) in xprt_free_slot()
> else
> xprt_free_bc_request(req);
> }
> I mean that in step 1, xprt was only released, but
> xprt_wake_up_backlog was not called (I don’t know if it is necessary,
> but xprt->state may still be XPRT_CONGESTED), which causes xprt to
> hold up. I think it happens when the task that does not hold a slot
> is the last released task,xprt_wake_up_backlog(clear XPRT_CONGESTED)
> will not be executed. :-)
> Thanks,
> Bixuan Cui
>
>
My point is that in that case 1, there is no slot to free, so there is
no change to the congestion state.
IOW: your patch is incorrect because it is trying to assign a slot in a
case where there is no slot to assign.
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com
next prev parent reply other threads:[~2021-12-22 15:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-14 13:53 [PATCH -next] SUNRPC: Clean XPRT_CONGESTED of xprt->state when rpc task is killed Bixuan Cui
2021-12-14 13:53 ` Bixuan Cui
2021-12-20 3:39 ` Bixuan Cui
2021-12-20 18:22 ` Trond Myklebust
[not found] ` <efbf73f3-c6cd-90f6-ef22-bde14be708cc@linux.alibaba.com>
2021-12-22 15:02 ` Trond Myklebust [this message]
2021-12-31 2:00 ` Bixuan Cui
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