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@xxxxxxxxxxxxxxx
