linux-kernel - Re: Possible bug report: kernel 6.5.0/6.5.1 high load when CIFS share is mounted (cifsd-cfid-laundromat in"D" state)

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Date:   Thu, 5 Oct 2023 04:59:36 -0500
From:   Steve French <smfrench@...il.com>
To:     "Dr. Bernd Feige" <bernd.feige@...klinik-freiburg.de>
Cc:     "tom@...pey.com" <tom@...pey.com>,
        "paul@...krain42.org" <paul@...krain42.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        "pc@...guebit.com" <pc@...guebit.com>,
        "ronniesahlberg@...il.com" <ronniesahlberg@...il.com>,
        "nspmangalore@...il.com" <nspmangalore@...il.com>,
        "brian.pardy@...il.com" <brian.pardy@...il.com>,
        "bharathsm@...rosoft.com" <bharathsm@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Possible bug report: kernel 6.5.0/6.5.1 high load when CIFS share
 is mounted (cifsd-cfid-laundromat in"D" state)

FYI - Paulo is looking at an additional patch to address this (and one
small patch was also just added)

On Thu, Oct 5, 2023 at 4:55 AM Dr. Bernd Feige
<bernd.feige@...klinik-freiburg.de> wrote:
>
> Am Dienstag, dem 26.09.2023 um 17:54 -0700 schrieb Paul Aurich:
> > Perhaps the laundromat thread should be using msleep_interruptible()?
> >
> > Using an interruptible sleep appears to prevent the thread from
> > contributing
> > to the load average, and has the happy side-effect of removing the
> > up-to-1s delay
> > when tearing down the tcon (since a7c01fa93ae, kthread_stop() will
> > return
> > early triggered by kthread_stop).
>
> Sorry for chiming in so late - I'm also on gentoo (kernel 6.5.5-
> gentoo), but as a client of Windows AD.
>
> Just want to emphasize that using uninterruptible sleep has not just
> unhappy but devastating side-effects.
>
> I have 8 processors and 16 cifsd-cfid-laundromat processes, so
> /proc/loadavg reports a load average of 16 on a totally idle system.
>
> This means that load-balancing software will never start additional
> tasks on this system - "make -l" but also any other load-dependent
> system. Just reducing the number of cifsd-cfid-laundromat processes
> does not fix this - even a single one makes loadavg report a wrong
> result for load balancing.
>
> So, if cifsd-cfid-laundromat must really be uninterruptible, the only
> solution would be to change the way loadavg is computed by the kernel
> to exclude uninterruptible but sleeping processes. But must it be
> uninterruptible?
>
> Thanks and best regards,
> Bernd



-- 
Thanks,

Steve