linux-kernel - div_u64/do_div stack size usage, was Re: [v3] block: Removed a warning while compiling with a cross compiler for parisc

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Message-ID: <YOSMct1YHs++E1vt@infradead.org>
Date:   Tue, 6 Jul 2021 18:01:38 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>,
        Bernardo Innocenti <bernie@...eler.com>,
        "torvalds@...ux-foundation.org Abd-Alrhman Masalkhi" 
        <abd.masalkhi@...il.com>
Cc:     hch@...radead.org, axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, dan.carpenter@...cle.com,
        linux-parisc@...r.kernel.org
Subject: div_u64/do_div stack size usage, was Re: [v3] block: Removed a
 warning while compiling with a cross compiler for parisc

On Tue, Jul 06, 2021 at 05:30:54PM +0200, Abd-Alrhman Masalkhi wrote:
> Thank you for your comment, the div_u64 function is called 5 times
> inside diskstats_show function, so I have made a test case; I have
> replaced one call with a constant number then I have compiled the 
> kernel, the result was instead of emitting "the frame size of 1656
> bytes is larger than 1280 bytes" warning, it has emitted "the frame
> size of 1328 bytes is larger than 1280 bytes" warning, so I came to the
> conclusion that each call to div_u64 will add 328 bytes to the stack
> frame of diskstats_show function, since it is an inlined function. so I
> thought it might be the solution that to preventing div_u64 to be
> inlined in diskstats_show function.

Adding a bunch of relevant parties to the CC list - any idea how we
can make the generic do_div / div_u64 not use up such gigantic amounts
of stack?