Re: [PATCH v2 04/15] fs: Restore write hint support

[Christoph Hellwig <hch@lst.de>]

On Thu, Oct 05, 2023 at 12:40:50PM -0700, Bart Van Assche wrote:
> This patch reverts a small subset of commit c75e707fe1aa ("block: remove
> the per-bio/request write hint"). The following functionality has been
> restored:

Please explain this in terms of what you add.  The fact that it restores
something isn't more than a little footnote added at the end.

> --- /dev/null
> +++ b/include/linux/fs-lifetime.h

The name seems a bit odd for something that primarily deals with bios.
bio-lifetime.h would seem like a better fit.

> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#include <linux/bio.h>
> +#include <linux/fs.h>
> +#include <linux/ioprio.h>
> +
> +static inline enum rw_hint bio_get_data_lifetime(struct bio *bio)
> +{
> +	/* +1 to map 0 onto WRITE_LIFE_NONE. */
> +	return IOPRIO_PRIO_LIFETIME(bio->bi_ioprio) + 1;

This seems a little to magic.  Why not a lookup table?

> +}
> +
> +static inline void bio_set_data_lifetime(struct bio *bio, enum rw_hint lifetime)

Please avoid the overly long line.

> +	/* -1 to map WRITE_LIFE_NONE onto 0. */
> +	if (lifetime != 0)
> +		lifetime--;
> +	WARN_ON_ONCE(lifetime & ~IOPRIO_LIFETIME_MASK);

I'd return here instead of propagating the bogus value.