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From:   Chengen Du <chengen.du@canonical.com>
Date:   Thu, 6 Apr 2023 10:55:46 +0800
Message-ID: <CAPza5qdyedpqdZYA3spd_L4v2goJbnjOqdu6TZuZ3qXXkqgCaA@mail.gmail.com>
Subject: Re: [NFS] Performance degradation due to commit 0eb43812c027 (NFS:
 Clear the file access cache upon login)
To:     trond.myklebust@hammerspace.com, Anna Schumaker <anna@kernel.org>
Cc:     linux-nfs@vger.kernel.org
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Hi Trond / Anna,

I apologize for disturbing you, as I understand that you may be
occupied with other tasks.
However, I wanted to bring to your attention that several users have
reported a performance issue, and are eagerly awaiting a possible
solution.

I have proposed a potential solution and I would be grateful if you
could provide me with some feedback.
Your input would be highly appreciated, as it will allow me to
continue working on this issue and finding a resolution for our users.

Thank you for your time and consideration.

Best regards,
Chengen Du

On Wed, Mar 29, 2023 at 1:48=E2=80=AFPM Chengen Du <chengen.du@canonical.co=
m> wrote:
>
> Hi Trond / Anna,
>
> I wanted to provide you with additional feedback regarding the
> performance issue that was addressed in commit 21fd9e8700de (NFS:
> Correct timing for assigning access cache timestamp).
> I apologize for reaching out to you frequently, but I believe this
> information is important to share.
>
> Although the commit appears to have resolved the issue, I have
> received reports from some community users who are experiencing a
> significant increase in NFS ACCESS operations.
> If you are interested, you can find further details regarding this
> feedback here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/20093=
25
>
> After conducting a survey, I have discovered that this issue may be
> attributed to suexec-like mechanisms.
> Specifically, applications or users may use the 'su' command to switch
> to other privileged users and operate on NFS-mounted folders.
> In these instances, the login time will be renewed, and NFS ACCESS
> operations will need to be resent.
>
> While I believe the new mechanism adheres to POSIX design and the
> performance overhead seems reasonable,
> I think it would be beneficial to provide a mount option that allows
> users to decide whether to renew access cache after login.
> In some production environments where access cache can be trusted due
> to the stable group membership, this option could be particularly
> useful.
>
> In my humble opinion, the option could be enabled by default for most
> personal users who can afford the overhead.
> However, I am open to hearing your thoughts on this approach or any
> alternative ideas you may have.
> I would be willing to contribute to this effort if there is an opportunit=
y.
>
> Thank you for your time and consideration.
>
> Best regards,
> Chengen Du