linux-kernel - Re: [PATCH] fork: Use THREAD_SIZE

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Message-Id: <8f27c774-7197-48da-a6f2-6d375bd848f0@app.fastmail.com>
Date: Mon, 11 Mar 2024 14:47:31 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Geert Uytterhoeven" <geert@...ux-m68k.org>,
 "Andrew Morton" <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fork: Use THREAD_SIZE_ORDER

On Mon, Mar 11, 2024, at 14:44, Geert Uytterhoeven wrote:
> Use the existing THREAD_SIZE_ORDER definition instead of calculating it
> from THREAD_SIZE and PAGE_SIZE.
>
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
>  kernel/fork.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 0d944e92a43ffa13..e79fdfe1f0bf4953 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -252,9 +252,9 @@ static int memcg_charge_kernel_stack(struct vm_struct *vm)
>  	int ret;
>  	int nr_charged = 0;
> 
> -	BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
> +	BUG_ON(vm->nr_pages != THREAD_SIZE_ORDER);
> 

That doesn't look right, THREAD_SIZE_ORDER not the number of
pages but the the log2 of it, right?

I think you want '(1 << THREAD_SIZE_ORDER)', but at that point
it doesn't actually look simpler than the existing code.

    Arnd