在 2021/12/22 下午11:02, Trond Myklebust 写道:
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.
Hi，
I found the correct way to fix it, that is, do not free the request when
there are tasks in the xprt->backlog :-)
And it has been fixed by e877a88d1f06 (SUNRPC in case of backlog, hand
free slots directly to waiting task)
commit e877a88d1f069edced4160792f42c2a8e2dba942
Author: NeilBrown <neilb@xxxxxxx>
Date: Mon May 17 09:59:10 2021 +1000
SUNRPC in case of backlog, hand free slots directly to waiting task
If sunrpc.tcp_max_slot_table_entries is small and there are tasks
on the backlog queue, then when a request completes it is freed and the
first task on the queue is woken. The expectation is that it will wake
and claim that request. However if it was a sync task and the waiting
process was killed at just that moment, it will wake and NOT claim the
request.
Thanks for your advice.
Thanks,
Bixuan Cui
