linux-kernel - Re: [PATCH v3 2/2] blk-throttle: kill the no longer needed overflow check in calculate_bytes

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Message-ID: <20250817135013.7567dd13@pumpkin>
Date: Sun, 17 Aug 2025 13:50:13 +0100
From: David Laight <david.laight.linux@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, Ingo
 Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas
 Gleixner <tglx@...utronix.de>, Li RongQing <lirongqing@...du.com>, Yu Kuai
 <yukuai3@...wei.com>, Khazhismel Kumykov <khazhy@...omium.org>, Jens Axboe
 <axboe@...nel.dk>, linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v3 2/2] blk-throttle: kill the no longer needed overflow
 check in calculate_bytes_allowed()

On Fri, 15 Aug 2025 18:41:02 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> Now that mul_u64_u64_div_u64() can't crash there is no need to check for
> possible overflow in calculate_bytes_allowed().
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  block/blk-throttle.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index 397b6a410f9e..66339e22cc85 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -601,12 +601,6 @@ static unsigned int calculate_io_allowed(u32 iops_limit,
>  
>  static u64 calculate_bytes_allowed(u64 bps_limit, unsigned long jiffy_elapsed)
>  {
> -	/*
> -	 * Can result be wider than 64 bits?
> -	 * We check against 62, not 64, due to ilog2 truncation.
> -	 */
> -	if (ilog2(bps_limit) + ilog2(jiffy_elapsed) - ilog2(HZ) > 62)
> -		return U64_MAX;
>  	return mul_u64_u64_div_u64(bps_limit, (u64)jiffy_elapsed, (u64)HZ);

Not directly related, but the two (u64) casts are pointless and can be removed.

	David

>  }
>