On Mar 20, 2015, at 12:15 PM, Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote:
> Chuck pointed out a problem that crept in with commit 6ffa30d3f734 (nfs:
> don't call blocking operations while !TASK_RUNNING). Linux counts tasks
> in uninterruptible sleep against the load average, so this caused the
> system's load average to be pinned at at least 1 when there was a
> NFSv4.1+ mount active.
>
> Not a huge problem, but it's probably worth fixing before we get too
> many complaints about it. This patch converts the code back to use
> TASK_INTERRUPTIBLE sleep, simply has it flush any signals on each loop
> iteration. In practice no one should really be signalling this thread at
> all, so I think this is reasonably safe.
>
> With this change, there's also no need to game the hung task watchdog so
> we can also convert the schedule_timeout call back to a normal schedule.
>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
Thanks for the quick response, Jeff.
I applied this on top of the first patch, mounted a test filesystem
with NFSv4.1, and confirmed that the backchannel service is responsive.
Load average on the client at idle is now 0.01.
Tested-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Nit: I’d add a Fixes: commit 6ffa30d3f734 (“nfs: don't call blocking . . .”)
tag.
> ---
> fs/nfs/callback.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
> index 351be9205bf8..8d129bb7355a 100644
> --- a/fs/nfs/callback.c
> +++ b/fs/nfs/callback.c
> @@ -128,7 +128,7 @@ nfs41_callback_svc(void *vrqstp)
> if (try_to_freeze())
> continue;
>
> - prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_UNINTERRUPTIBLE);
> + prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
> spin_lock_bh(&serv->sv_cb_lock);
> if (!list_empty(&serv->sv_cb_list)) {
> req = list_first_entry(&serv->sv_cb_list,
> @@ -142,10 +142,10 @@ nfs41_callback_svc(void *vrqstp)
> error);
> } else {
> spin_unlock_bh(&serv->sv_cb_lock);
> - /* schedule_timeout to game the hung task watchdog */
> - schedule_timeout(60 * HZ);
> + schedule();
> finish_wait(&serv->sv_cb_waitq, &wq);
> }
> + flush_signals(current);
> }
> return 0;
> }
> --
> 2.1.0
>
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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