linux-kernel - Re: [PATCH net-next v2] openvswitch: reduce stack usage in do_execute

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Message-ID: <CANn89iJxrsgeS_FOivxPdYLhPyLC6Lo8VBzLjdx9-mQKXxqjwA@mail.gmail.com>
Date:   Thu, 21 Sep 2023 21:58:27 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Ilya Maximets <i.maximets@....org>
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        dev@...nvswitch.org, Pravin B Shelar <pshelar@....org>,
        Eelco Chaudron <echaudro@...hat.com>
Subject: Re: [PATCH net-next v2] openvswitch: reduce stack usage in do_execute_actions

On Thu, Sep 21, 2023 at 9:42 PM Ilya Maximets <i.maximets@....org> wrote:
>
> do_execute_actions() function can be called recursively multiple
> times while executing actions that require pipeline forking or
> recirculations.  It may also be re-entered multiple times if the packet
> leaves openvswitch module and re-enters it through a different port.
>
> Currently, there is a 256-byte array allocated on stack in this
> function that is supposed to hold NSH header.  Compilers tend to
> pre-allocate that space right at the beginning of the function:
>
>      a88:       48 81 ec b0 01 00 00    sub    $0x1b0,%rsp
>
> NSH is not a very common protocol, but the space is allocated on every
> recursive call or re-entry multiplying the wasted stack space.
>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>