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:   Tue, 19 Sep 2023 13:23:44 -0500
From:   Steve French <smfrench@...il.com>
To:     Tom Talpey <tom@...pey.com>
Cc:     Brian Pardy <brian.pardy@...il.com>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Linux CIFS <linux-cifs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Paulo Alcantara <pc@...guebit.com>,
        ronnie sahlberg <ronniesahlberg@...il.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Bharath S M <bharathsm@...rosoft.com>
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)

On Tue, Sep 19, 2023 at 1:07 PM Tom Talpey <tom@...pey.com> wrote:
>
> On 9/19/2023 9:38 AM, Steve French wrote:
> > Minor updates (pointed out by Paulo) to patch. See attached.
>
> So, was the thread crashing before??
>
> +       if (cfids == NULL)
> +               return;
> +

Without laundromat initialized cfids can be null - so we need to check
if cfids is initialized in a few places (may help in a few corner
cases if there is a race in closing laundromat thread at umount but
was added to avoid oops at unmount if laundromat not initialized)

> These changes are good, but I'm skeptical they will reduce the load
> when the laundromat thread is actually running. All these do is avoid
> creating it when not necessary, right?

It does create half as many laundromat threads (we don't need
laundromat on connection to IPC$) even for the Windows server target
example, but helps more for cases where server doesn't support
directory leases.

> > On Tue, Sep 19, 2023 at 8:21 AM Brian Pardy <brian.pardy@...il.com> wrote:
> >>
> >> On Tue, Sep 19, 2023 at 1:36 AM Steve French <smfrench@...il.com> wrote:
> >>>
> >>> Does the attached patch help in your case?  It avoids starting the
> >>> laundromat thread for IPC shares (which cuts the number of the threads
> >>> in half for many cases) and also avoids starting them if the server
> >>> does not support directory leases (e.g. if Samba server instead of
> >>> Windows server).
> >>
> >> Hello,
> >>
> >> I applied the 0001-smb3-do-not-start-laundromat-thread-when-dir-leases-.patch
> >> you provided against the 6.5.3 kernel.
> >>
> >> I can confirm that it resolves this issue - no laundromat threads are
> >> created, and the reported load average is as expected, not falsely
> >> high.
> >>
> >> This appears to fully fix the issue in my case.  Thank you very much!
> >>
> >>> On Mon, Sep 18, 2023 at 10:00 PM Steve French <smfrench@...il.com> wrote:
> >>>>
> >>>> Paulo and I were discussing the laundromat thread at the SMB3.1.1 test
> >>>> event (at SDC this week) which is now going on - will let you know
> >>>> what we find.
> >>>>
> >>>> One obvious thing is that it probably isn't necessary for cases when
> >>>> the server does not support directory leases, but we noticed another
> >>>> problem as well.
> >
> >
> >



-- 
Thanks,

Steve