linux-kernel - Re: [PATCH] btrfs: scrub: replace max_t()/min_t() with clamp_t() in scrub_throttle_dev

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Message-ID: <20250908183655.GT5333@suse.cz>
Date: Mon, 8 Sep 2025 20:36:55 +0200
From: David Sterba <dsterba@...e.cz>
To: David Laight <david.laight.linux@...il.com>
Cc: Thorsten Blum <thorsten.blum@...ux.dev>, Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: scrub: replace max_t()/min_t() with clamp_t() in
 scrub_throttle_dev_io()

On Sat, Sep 06, 2025 at 12:24:58PM +0100, David Laight wrote:
> On Mon,  1 Sep 2025 17:01:44 +0200
> Thorsten Blum <thorsten.blum@...ux.dev> wrote:
> 
> > Replace max_t() followed by min_t() with a single clamp_t(). Manually
> > casting 'bwlimit / (16 * 1024 * 1024)' to u32 is also redundant when
> > using max_t(u32,,) or clamp_t(u32,,) and can be removed.
> > 
> > No functional changes intended.
> > 
> > Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> > ---
> >  fs/btrfs/scrub.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> > index 6776e6ab8d10..ebfde24c0e42 100644
> > --- a/fs/btrfs/scrub.c
> > +++ b/fs/btrfs/scrub.c
> > @@ -1369,8 +1369,7 @@ static void scrub_throttle_dev_io(struct scrub_ctx *sctx, struct btrfs_device *d
> >  	 * Slice is divided into intervals when the IO is submitted, adjust by
> >  	 * bwlimit and maximum of 64 intervals.
> >  	 */
> > -	div = max_t(u32, 1, (u32)(bwlimit / (16 * 1024 * 1024)));
> > -	div = min_t(u32, 64, div);
> > +	div = clamp_t(u32, bwlimit / (16 * 1024 * 1024), 1, 64);
> 
> That probably ought to have a nack... although it isn't different.
> bwlimit is 64bit, if very big dividing by 16M will still be over 32 bits.
> and significant bits will be lost.
> 
> Just use clamp() without all the extra (bug introducing) (u32) casts.

Clamp without type works best, thanks. The bug with large values could
happen, but the input value is expected to be in gigabytes range.